|Year : 2011 | Volume
| Issue : 6 | Page : 823-834
Low-cost assays for monitoring HIV infected individuals in resource-limited settings
Pachamuthu Balakrishnan1, Hussain Syed Iqbal1, Saravanan Shanmugham1, Janardhanan Mohanakrishnan1, Sunil S Solomon2, Kenneth H Mayer3, Suniti Solomon1
1 YRG Centre for AIDS Research & Education, Chennai, India
2 YRG Centre for AIDS Research & Education, Chennai, India; Division of Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, USA
3 Brown University, RI, Providence, USA
|Date of Submission||30-Sep-2011|
|Date of Web Publication||6-Feb-2012|
YRG Centre for AIDS Research & Education, Voluntary Health Services, Taramani, Chennai 600 113, India
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Use of a combination of CD4 counts and HIV viral load testing in the management of antiretroviral therapy (ART) provides higher prognostic estimation of the risk of disease progression than does the use of either test alone. The standard methods to monitor HIV infection are flow cytometry based for CD4+ T cell count and molecular assays to quantify plasma viral load of HIV. Commercial assays have been routinely used in developed countries to monitor ART. However, these assays require expensive equipment and reagents, well trained operators, and established laboratory infrastructure. These requirements restrict their use in resource-limited settings where people are most afflicted with the HIV-1 epidemic. With the advent of low-cost and/or low-tech alternatives, the possibility of implementing CD4 count and viral load testing in the management of ART in resource-limited settings is increasing. However, an appropriate validation should have been done before putting them to use for patient testing.
Keywords: CD4 count - HIV monitoring - low-cost assays - plasma viral load - resource-limited settings
|How to cite this article:|
Balakrishnan P, Iqbal HS, Shanmugham S, Mohanakrishnan J, Solomon SS, Mayer KH, Solomon S. Low-cost assays for monitoring HIV infected individuals in resource-limited settings. Indian J Med Res 2011;134:823-34
|How to cite this URL:|
Balakrishnan P, Iqbal HS, Shanmugham S, Mohanakrishnan J, Solomon SS, Mayer KH, Solomon S. Low-cost assays for monitoring HIV infected individuals in resource-limited settings. Indian J Med Res [serial online] 2011 [cited 2020 Jan 21];134:823-34. Available from: http://www.ijmr.org.in/text.asp?2011/134/6/823/92628
| Introduction|| |
The cost of antiretroviral therapy (ART) has reduced dramatically due to the production by generic manufactures and this has led to the increased usage of ART in developing countries. As ART is becoming more affordable and accessible, inexpensive laboratory tests are also needed to monitor the progression of disease in HIV infected individuals living in resource-limited settings, where HIV burden is usually high  . HIV treatment can be managed without routine laboratory assessment  , but CD4+ T cell count monitoring allows the evaluation of disease progression  , and viral load testing can increase adherence and facilitate timely switching of failing regimens, minimizing the development of resistance , . Thus, use of a combination of CD4 counts and HIV viral load testing in the management of ART provides higher prognostic estimation of the risk of disease progression than does the use of either test alone , .
Historically, several candidate markers have been explored for monitoring the course of HIV infection and response to treatment. Though several new parameters are being evaluated , , the levels of absolute numbers of peripheral CD4+ T cells (immunological marker) and the viral load (virological marker) have eventually become the reference markers in clinical practice for monitoring HIV infected individuals. These indicators are used to determine disease stage and progression, and assist in making decisions regarding when to start or change ART regimens, and assess treatment responses  . The lack of infrastructure for laboratory monitoring of HIV disease is one of the major reasons for ineffective implementation of ART roll-out programmes in several resource-limited settings in the developing countries  .
The reference standard for CD4+ T cell testing is enumeration of T cell subsets by flow cytometry. For plasma viral load (PVL), a number of nucleic acid test (NAT) based assays that use reverse transcriptase-polymerase chain reaction (RT-PCR), branched DNA (b-DNA), and nucleic acid sequence based amplification (NASBA) technologies are approved in many countries. Such reference assays are prohibitively expensive and also require sophisticated infrastructure facilities with expensive laboratory equipment as well as trained technical personnel, which are not widely available in resource-limited countries  . The high initial cost of equipment and problems associated with equipment routine maintenance, lack of technical support, and lack of access to quality assurance/control (QA/QC) programmes have limited widespread use of standard methodologies. This review addresses the importance of newer alternative methodologies, which are low-cost and low-tech for the use in resource-limited settings.
| The Reference Standard and Low-Cost Monitoring of CD4+ T-Cell Count|| |
CD4+ T cell monitoring in conjunction with clinical status will be of benefit in terms of assessing prognosis and guiding the treatment response. Also, CD4+ T cell count allows timely administration of primary prophylaxis against specific opportunistic infections (OIs) and an associated reduction in hospital admissions, with use of affordable drugs such as trimethoprim sulphamethoxazole  . The precise CD4+ T cell count at which the risk of specific OIs justifies prophylaxis has been well established in the western countries  .
The reference standard for CD4+ T cell count: Multi-parameter flow cytometric quantification of CD4+ T cells with microprocessor-assisted analysis is the reference standard. A wide range of instruments are available commercially from different companies including the popular manufacturers' flow cytometry, Becton Dickinson and Beckman Coulter Corporation  . The cost of reagents to perform full lymphocyte subset multi-platform analysis, in which CD45+ T cells are identified by staining with 8 monoclonal antibodies (MAbs) by means of 3-colour fluorescence to identify CD3+/CD4+ and CD3+/CD8+ T cells, is also prohibitive in many countries. Among the available flow cytometers, the FACSCount (Becton Dickinson) instrument is a simpler, relatively less expensive and automated for clinical laboratories and quantifies CD4+/CD8+ T cell counts by simultaneous fluorescent MAb staining of CD3, CD4, and CD8 surface molecules by use of different fluorochromes attached to each MAb.
Low-cost alternative assays for CD4+ T cell count: Currently several modified flow cytometry and new gating approaches are available to make the assay low-cost and low-tech without compromising the quality of the test results. The assays with modified flow cytometry technologies (volumetric system) are EasyCD4 and CyFlow. Extensive evaluation studies have been carried out with these modified flow cytometry in different countries on the efficiency of the each assay in providing accurate and reproducible results ,,,,, . New approaches also include primary gating, in which CD4+ T cells are defined by an autogate in a single histogram of CD4+ T cell fluorescence intensity versus light scatter by use of a single-platform volumetric flow cytometry. This is considered relatively economical compared with the use of full test panel of MAbs  . The summary of the different low-cost assays of CD4+ T cell count and evaluation studies data are shown in [Table 1] and [Table 2].
|Table 2: Summary of validation data of alternate low-cost assays of CD4 T cell count|
Click here to view
Guava EasyCD4 assay is a micro-capillary flow cytometry technology based system made by Millipore-Guava Technologies, USA. The flow cytometer is coupled with a laptop computer for analysis. The system uses a diode green laser as a light source. The reagent kit consists of two monoclonal antibodies directly conjugated to PECy5 and PE for CD3 and CD4 T-cell antigens. The procedure does not require sheath fluid and the system's sampling precision depends on the integrity of the fluid pathway. Studies ,, from other settings and at Chennai, India  have shown it easy to perform, and generate reliable results. Bland-Altman analysis showed close agreement with the EasyCD4 assay yielding CD4+ T-cell counts with a mean difference of -26 cells/μl higher than by flow cytometry. However, EasyCD4 is less accurate at high absolute CD4+ T-cell counts, particularly when the count is more than 500 cells/μl. This may be due to the standardization and optimization of these alternative assays to provide better results at the lower critical CD4+ T-cell counts. The technicians need substantially less training than the standard flow cytometry for this assay and it requires less volume of specimen (10 μl) and generates very minimal biowaste. Studies from other settings have also shown the good results ,,, .
CyFlow is another desktop single-platform technology made by Partec, Germany. It is a volumetric software controlled absolute count system equipped with either a single 532 nm green solid-state laser used for one fluorescence parameter or two lasers with a mercury arc lamp applicable for 2 or 3-colour analyses. Data acquisition and analysis are performed in real time with FlowMax software. It also can be used as a mobile system that can run on car batteries. It works on simple no-lyse and no-wash protocol. The machine is more robust than conventional flow cytometry and this mobile CD4+ T cell testing laboratory can be established for the field level use. Investigators from several resource-limited settings have evaluated the precision of the CyFlow system and observed good correlation with the standard assay ,,,,, .
PointCare NOW system is a mobile technology developed by PointCare Technologies Inc., USA. This DualZone (ImmuZone and HemaZone) technology provides two categories of testing: CD4 and CD4 per cent, combined with haematology profile (including haemoglobin and white cell differentials). Full automation and closed-capsampling make this system easy and safe to use, with minimal training. Heat-stable reagents eliminate cold-chain shipping. This instrument operates on the QuadScatter optical system with CD4 antibodies tagged to gold nano-particles. The CD4 T-cells are identified using a PointSmart primary gating strategy. This method eliminates the high energy consumption of the lasers that are used in traditional fluorescence-based methods. A whole blood sample (2 ml) is placed in the machine and after a single button operation CD4 results are generated in about 10 min. This machine can work on a battery back-up. Although this system has several advantages, evaluation studies are not sufficient in the peer-reviewed literature  .
Recently introduced PIMA point-of-care (POC) CD4 analyzer by Alere, USA, is becoming more attractive in resource-limited settings. It has major advantage in providing immediate clinical decision-making and fast programme delivery. This POC CD4 test uses disposable cartridges and as a battery-powered analyzer. Although it has additional advantage as use of a finger prick specimen, the performance on finger prick blood is not as good as on venous blood  . The performance of the venous blood have shown to give better results ,,, .
The CD45 gating approach combined with the use of fluorescence beads in the procedure has converted the standard flow cytometry into a single-platform approach. This gating approach also eliminates the need for multiple equipment (flow cytometry and haematology) and should be less expensive than the available methods when labour, cost and inconvenience of repeat samples, and haematology costs are considered. These absolute count tubes contain a lyophilized pellet that dissolves during sample preparation, releasing a known number of fluorescent beads. By gating the bead population during analysis, absolute cell counts can be readily determined by a simple calculation. Currently, the reagents are also available in the kit format from Beckman Coulter Inc., USA. This methodology has been validated in several settings and an excellent performance has been documented with multicentric studies ,,,, . The major advantage with this CD45 gating approach is analyzing aged samples even beyond 3 days storage.
A newly introduced single tube reagent from Becton Dickinson for FACSCount has several advantages particularly, being low-cost and also provides both CD4+ absolute count and its percentage. However, the validation data are very limited.
Flow cytometry versus low-cost assays to enumerate CD4+T cell count: Though the flow cytometry is considered the reference standard, disadvantages include the fact that, it is expensive in terms of initial cost of equipment and an ongoing operational cost including annual maintenance contract. Highly trained personnel are generally needed to run the standard flow cytometry, which are technically complicated and very often company technical support is needed. Most of the newer low-cost methodologies are simple to operate and robust. It could provide both absolute CD4+ T cell count and CD4+ T cell percentage; and is very useful as a built-in control to determine whether the CD4+ T cell count is changing or stable, is available  . Also biological variables, including diurnal variation, exercise or rest, and smoking, can significantly alter absolute CD4+ T cell count  . Most importantly, CD4+ T cell percentage is essential for monitoring paediatric cases.
Although manual CD4 count method using microbead system (Dynal Biotech, Oslo, Norway) has been shown to be good , , there are issues with the implementation in resource-limited settings such as labour intensive, low-throughput and requirement of qualified personnel for making accurate measurements. The POC testing device such as LabNow Inc., USA  or dipstick technology (personnel communication from Prof. Suzanne Crowe, Head, Pathogenesis and Clinical Research Program, Macfarlane Burnet Institute for Medical Research and Public Health, Melbourne, Australia) with a visual read-out format are currently under field level evaluation.
| The Reference Standard and Low-Cost Methods for Monitoring of Viral Load|| |
Viral load testing is the only definitive method for early detection of ART failure , . Assessment of viral load is one of the best predictors of HIV disease progression, as well as the main parameter to assess ART response. Multi-center AIDS Cohort Study (MACS) demonstrated that plasma HIV-RNA load was a better predictor of progression to AIDS and death than CD4 + T-cell counts , . But, the viral load testing has not been routinely implemented in resource-limited settings due to cost, complexity, availability and accessibility.
Commercial RNA viral load assays have been widely used as the 'gold standard' to quantify HIV-1 RNA in plasma  . Three major diagnostic companies, Roche (Roche Amplicor), bioMerieux (NASBA) and Siemens (b-DNA) have developed HIV-1 viral load assays. Compared to previous end-point detection methodologies, recently companies (Roche TaqMan and Abbott m2000rt) have adapted the real-time technologies based on ﬂuorescence to achieve simultaneous ampliﬁcation and detection instead of end-point detection  . The real-time technologies offer more accurate quantiﬁcation, a wider dynamic range, and a higher throughput. In addition, these companies have included automated sample preparation to reduce manual time and prevent carry-over contamination  . Most importantly, these assays extend the subtype coverage to detect increasing numbers of non-B strains, which are prevalent in most affected countries. However, these standard viral load assays are prohibitively expensive for the use in resource-limited settings and require very sophisticated infrastructure facilities.
Monitoring HIV-1 viral load in resource-limited settings faces multiple challenges particularly; (i) viral load monitoring is only available in reference laboratories, where various clinical trials are ﬁnancially supported by national and/or international funding, (ii) hospital facilities lack basic laboratory infrastructure such as reliable power and water supply and air conditioning, (iii) personnel with lack of training on technologically complex molecular assays, and (iv) not being robust methods.
To provide viral load monitoring in resource-limited settings, inexpensive alternative methodologies have been developed by different manufacturers and some of these have been validated in the recent years [Table 3] & [Table 4], such as the Cavidi ExaVir™ RT assay ,,,, , the PerkinElmer Ultrasensitive p24 assay ,- and homebrew RT-qPCR  . The ExaVir™ assay and the Ultrasensitive p24 assay are based on ELISA method, measuring the activity of reverse transcriptase (RT) enzyme and the concentration of p24 antigen, respectively. These alternative methods have signiﬁcantly reduced cost ($15-20), compared with commercial viral load assays ($70-100)  . Moreover, the ExaVir™ assay and the Ultrasensitive p24 assay are technologically simpler than standard viral load assays, and thus do not require highly skilled operators and advanced laboratory facilities. But these assay are time-consuming and labour intensive procedures. Although homebrew RT-qPCR methods are highly correlated with standard viral load assays, these still need expensive PCR thermal cyclers and highly trained operators, which restrict their application in decentralized laboratories  .
The Cavidi ExaVir™ RT assay is an ELISA-based assay to measure the RT activity, which in turn correlates well with the standard viral load assays. The equipment needed (which are provided by the company as a start-up kit at free of cost) is mainly a vacuum pump, waste bottle, some rubber tubing and an ELISA reader or a fluorometer and some buckets for the wash procedures. The procedure has only 2 major steps (purification of virions and recovery of RT, including removal of potential inhibitors, followed by quantification of RT activity in a microtitre plate format). In brief, HIV-1 virions are ﬁrst puriﬁed from plasma specimens using a solid phase extraction manifold to remove contaminants and inhibitors. Puriﬁed HIV-1 virions are then lysed to release RT enzyme. The released RT is added to a microtitre plate, which is coated with poly-A oligonucleotides. RT incorporates BrdUTP into cDNA, using the poly-A oligonucleotides as templates. After incubation at 33°C for 40 h, an alkaline phosphatase-conjugated anti-BrdU antibody and a substrate are sequentially added to achieve colorimetric detection. The colour intensity measured at a wavelength of 405 nm correlates with the RT activity. The RT activity of unknown samples is compared to those obtained from quantiﬁcation standards, reporting the viral load as fg/RT/ml or as HIV-1 RNA equivalents/ml.
The ExaVir™ RT assay is not affected by the presence of RT inhibitors (drugs) in plasma of HIV patients. Some of the challenges with this assay are requirement of 1 ml of plasma, lengthy testing procedure, and processing limited number of samples per operator per day. The performance of the assay has been documented from different parts of the world including validation at our Centre  . However, with improved performance, the recent ExaVir™ version 3.0, has a detection limit of as low as 200 RNA copies/ml, shortened turnaround time (48-72 h) and increased throughput (120 to 180 samples per week per operator). This RT assay was strongly correlated with the Roche Amplicor (r=0.8554), leading to implementation at four district hospital laboratories in Botswana  . However, it should be noted that the ExaVir™ RT assay is a functional assay; heavily mutated RT or co-infection with other retroviruses (e.g., HTLV-I) may interfere with its performance.
The PerkinElmer Ultrasensitive p24 assay is also based on ELISA to measure the concentration of HIV-1 p24 antigen, which has been shown to be strongly correlated with standard viral load assay  . Prior to the capture of p24 by a speciﬁc antibody-coated 96-well plate, specimens are lysed by a special kit buffer and incubated at 100°C for 5 min to release p24 molecules to a maximum degree from HIV-1 virions and from the p24/antibody complex in plasma. The captured p24 antigen is recognized by a biotinylated anti-p24 antibody, followed by the colorimetric detection step using a streptavidin-horseradish peroxidase conjugate. The emitted colour intensity of each sample is compared to intensities emitted from external standards of known concentrations, determining the level of p24. Although the Ultrasensitive p24 assay has shown a good correlation with standard viral load assays in some settings , , discordant results have also been observed in a study from Spain  . One study observed that the Ultrasensitive p24 assay detected 66.7 per cent of the specimens with viral load less than 10,000 copies/ml, and 87 per cent of the specimens with viral load of between 10,000 and 100,000 copies/ml  . Lombart et al has shown that only 27 per cent of the specimens were detected with viral load less than 1,000 copies/ml.
Homebrew RT-qPCR assays target a highly sequence-conserved region within the LTR to maximize the subtype coverage, which are more diverse in resource-limited settings than in developed countries. Rouet et al have shown that homebrew RT-qPCR correlates well with the standard assays. Although the test cost of the homebrew assay is signiﬁcantly reduced compared to commercial viral load assays, it still needs high-cost equipment, laboratory infrastructure and well-trained operators, restricting their use to district laboratories in rural areas.
The use of dried blood spot (DBS) is an interesting alternative to make the shipment of blood samples easier to the testing laboratories for performing HIV viral load test. Several studies have demonstrated that DBS are convenient for viral load measurements ,,, , although the sensitivity range and correlation with plasma values need to be determined for each commercial assay. Considering that the WHO guidelines  recommend switching therapy with viral loads above 5,000 copies/ml, the sensitivity obtained with DBS seems to be adequate at this time.
Recently several new approaches have been adopted to reduce the cost of viral load testing and also to ship the sample for viral testing. A new hypothesis was that pooled NAT (mini pools of 5 or 10 samples) could reduce the number of viral load assays needed to screen a population of patients on ART for virologic failure, and this costs lesser than individual viral load testing, which could make virologic monitoring feasible in resource-limited settings  . This method was found to be more than 40 per cent more efficient than individual viral load testing while maintaining excellent accuracy in a population with a prevalence of ART failure of 23 per cent  . However, this method need wider evaluation in a resource-limited setting before they could potentially be used as low cost method to make it for routine use for virologic monitoring purpose. SampleTanker  is another novel dried specimen technology and transport medium developed by Research Think Tank (RTT) for the collection and transportation of biological specimens for HIV-1 plasma RNA quantification and genotypic drug resistance testing in a dry state. This technology has been developed to allow for the biological testing of air-dried samples without the need for refrigeration or frozen shipping and storage. This technology has the potential to significantly reduce the costs of shipping infectious materials worldwide.
| Conclusion|| |
Every effort should be made to introduce appropriate laboratory monitoring assays in resource-limited settings, since the benefit of the scaling-up of ART seems to be largely dependent on adequate laboratory monitoring. Sustainability of assays [recognizing issues such as ongoing costs, delivery of reagents and kits, kit shelf-life, access to technical support and external quality assurance schemes (EQAS) programmes] must also be considered at the time of implementation. Importantly, the newer assays should be validated sufficiently to ensure that the results are accurate and reproducible. Further, much simpler tests, based on dip-stick technology or other POC assays, are needed and some are in the process of development or under field evaluation.
| References|| |
|1.||Katabira ET, Oelrichs RB. Scaling up antiretroviral treatment in resource-limited settings: successes and challenges. AIDS 2007; 21 : S5-10. |
|2.||Mugyenyi P, Walker AS, Hakim J, Munderi P, Gibb DM, Kityo C, et al. Routine versus clinically driven laboratory monitoring of HIV antiretroviral therapy in Africa (DART): a randomised non-inferiority trial. Lancet 2010; 375 : 123-31. |
|3.||Alex C. Utility of routine viral load, cd4 cell count, and clinical monitoring among hiv-infected adults in Uganda: A randomized trial. 2008. Available from: http://www.retroconference.org/2008/Abstracts/30881.htm, accessed on December 28, 2011. |
|4.||Keiser O, Tweya H, Boulle A, Braitstein P, Schecter M, Brinkhof MWG, et al. Switching to second-line antiretroviral therapy in resource-limited settings: comparison of programmes with and without viral load monitoring. AIDS 2009; 23 : 1867-74. |
|5.||Lynen L, Van Griensven J, Elliott J. Monitoring for treatment failure in patients on first-line antiretroviral treatment in resource-constrained settings. Curr Opin HIV AIDS 2010; 5 : 1-5. |
|6.||Mellors JW, Muñoz A, Giorgi JV, Margolick JB, Tassoni CJ, Gupta P, et al. Plasma viral load and CD4+ lymphocytes as prognostic markers of HIV-1 infection. Ann Intern Med 1997; 126 : 946-54. |
|7.||O'Brien WA, Hartigan PM, Daar ES, Simberkoff MS, Hamilton JD. Changes in plasma HIV RNA levels and CD4+ lymphocyte counts predict both response to antiretroviral therapy and therapeutic failure. VA Cooperative Study Group on AIDS. Ann Intern Med 1997; 126 : 939-45. |
|8.||Halota W, Jaruga B, Paw³owska M. [Serum neopterin and beta2-microglobulin concentration as "prognostic markers" of AIDS]. Pol Merkur Lekarski 2002; 13 : 126-8. |
|9.||Cheng B, Landay A, Miller V. Research needs and challenges in the development of HIV diagnostic and treatment monitoring tests for use in resource-limited settings. Curr Opin HIV AIDS 2008; 3 : 495-503. |
|10.||Planella T, Cortés M, Martínez-Brú C, Barrio J, Sambeat MA, González-Sastre F. The predictive value of several markers in the progression to acquired immunodeficiency syndrome. Clin Chem Lab Med 1998; 36 : 169-73. |
|11.||Fiscus SA, Cheng B, Crowe SM, Demeter L, Jennings C, Miller V, et al. HIV-1 viral load assays for resource-limited settings. PLoS Med 2006; 3 : e417. |
|12.||Wiktor SZ, Sassan-Morokro M, Grant AD, Abouya L, Karon JM, Maurice C, et al. Efficacy of trimethoprim-sulphamethoxazole prophylaxis to decrease morbidity and mortality in HIV-1-infected patients with tuberculosis in Abidjan, Côte d'Ivoire: a randomised controlled trial. Lancet 1999; 353 : 1469-75. |
|13.||Crowe SM, Carlin JB, Stewart KI, Lucas CR, Hoy JF. Predictive value of CD4 lymphocyte numbers for the development of opportunistic infections and malignancies in HIV-infected persons. J Acquir Immune Defic Syndr 1991; 4 : 770-6. |
|14.||Crowe S, Turnbull S, Oelrichs R, Dunne A. Monitoring of human immunodeficiency virus infection in resource-constrained countries. Clin Infect Dis 2003; 37 : S25-35. |
|15.||Zijenah LS, Kadzirange G, Madzime S, Borok M, Mudiwa C, Tobaiwa O, et al. Affordable flow cytometry for enumeration of absolute CD4+ T-lymphocytes to identify subtype C HIV-1 infected adults requiring antiretroviral therapy (ART) and monitoring response to ART in a resource-limited setting. J Transl Med 2006; 4 : 33-8. |
|16.||Fryland M, Chaillet P, Zachariah R, Barnaba A, Bonte L, Andereassen R, et al. The Partec CyFlow Counter could provide an option for CD4+ T-cell monitoring in the context of scaling-up antiretroviral treatment at the district level in Malawi. Trans R Soc Trop Med Hyg 2006; 100 : 980-5. |
|17.||Cecelia AJ, Balakrishnan P, Mohanakrishnan, Venkatakrishnan B, Solomon S, Kumarasamy N. Effective evaluation of novel low-cost CD4 monitoring assays. J Immunol Methods 2006; 316 : 158-62. |
|18.||Balakrishnan P, Solomon S, Mohanakrishnan J, Cecelia AJ, Kumarasamy N, Murugavel KG, et al. A reliable and inexpensive EasyCD4 assay for monitoring HIV-infected individuals in resource-limited settings. J Acquir Immune Defic Syndr 2006; 43 : 23-6. |
|19.||Kandathil AJ, Kannangai R, David S, Nithyanandam G, Solomon S, Balakrishnan P, et al. Comparison of microcapillary cytometry technology and flow cytometry for CD4+ and CD8+ T-Cell Estimation. Clin Diagn Lab Immunol 2005; 12 : 1006-9. |
|20.||Balakrishnan P, Dunne M, Kumarasamy N, Crowe S, Subbulakshmi G, Ganesh AK, et al. An inexpensive, simple, and manual method of CD4 T-cell quantitation in HIV-infected individuals for use in developing countries. J Acquir Immune Defic Syndr 2004; 36 : 1006-10. |
|21.||Janossy G, Jani I, Göhde W. Affordable CD4(+) T-cell counts on "single-platform" flow cytometers I. Primary CD4 gating. Br J Haematol 2000; 111 : 1198-208. |
|22.||Pattanapanyasat K, Sukapirom K, Kowawisatsut L, Thepthai C. New BD FACSCount CD4 reagent system for simultaneous enumeration of percent and absolute CD4 T-lymphocytes in HIV-1-infected pediatric patients. Cytometry B Clin Cytom 2008; 74 : S98-106. |
|23.||Pattanapanyasat K, Lerdwana S, Noulsri E, Chaowanachan T, Wasinrapee P, Sakulploy N, et al. Evaluation of a new single-parameter volumetric flow cytometer (CyFlow(green)) for enumeration of absolute CD4+ T lymphocytes in human immunodeficiency virus type 1-infected Thai patients. Clin Diagn Lab Immunol 2005; 12 : 1416-24. |
|24.||Thakar MR, Kumar BK, Mahajan BA, Mehendale SM, Paranjape RS. Comparison of capillary based microflurometric assay for CD4+ T cell count estimation with dual platform Flow cytometry. AIDS Res Ther 2006; 3 : 26-32. |
|25.||Pattanapanyasat K, Phuang-Ngern Y, Sukapirom K, Lerdwana S, Thepthai C, Tassaneetrithep B. Comparison of 5 flow cytometric immunophenotyping systems for absolute CD4+ T-lymphocyte counts in HIV-1-infected patients living in resource-limited settings. J Acquir Immune Defic Syndr 2008; 49 : 339-47. |
|26.||Pattanapanyasat K, Phuang-Ngern Y, Lerdwana S, Wasinrapee P, Sakulploy N, Noulsri E, et al. Evaluation of a single-platform microcapillary flow cytometer for enumeration of absolute CD4+ T-lymphocyte counts in HIV-1 infected Thai patients. Cytometry B Clin Cytom 2007; 72 : 387-96. |
|27.||Mtapuri-Zinyowera S, Chideme M, Mangwanya D, Mugurungi O, Gudukeya S, Hatzold K, et al. Evaluation of the PIMA point-of-care CD4 analyzer in VCT clinics in Zimbabwe. J Acquir Immune Defic Syndr 2010; 55 : 1-7. |
|28.||Diaw PA, Daneau G, Coly AA, Ndiaye BP, Wade D, Camara M, et al. Multisite evaluation of a point-of-care instrument for CD4(+) T-cell enumeration using venous and finger-prick blood: the PIMA CD4. J Acquir Immune Defic Syndr 2011; 58 : e103-11. |
|29.||Pattanapanyasat K, Shain H, Noulsri E, Lerdwana S, Thepthai C, Prasertsilpa V, et al. A multicenter evaluation of the PanLeucogating method and the use of generic monoclonal antibody reagents for CD4 enumeration in HIV-infected patients in Thailand. Cytometry B Clin Cytom 2005; 65 : 29-36. |
|30.||Sippy-Chatrani N, Marshall S, Branch S, Carmichael-Simmons K, Landis RC, Abayomi A. Performance of the Panleucogating protocol for CD4+ T cell enumeration in an HIV dedicated laboratory facility in Barbados. Cytometry B Clin Cytom 2008; 74 : S65-8. |
|31.||Diagbouga S, Chazallon C, Kazatchkine MD, Van de Perre P, Inwoley A, M'Boup S, et al. Successful implementation of a low-cost method for enumerating CD4+ T lymphocytes in resource-limited settings: the ANRS 12-26 study. AIDS 2003; 17 : 2201-8. |
|32.||Renault CA, Traore A, Machekano RN, Israelski DM. Validation of microcapillary flow cytometry for community-based CD4+ T lymphocyte enumeration in remote Burkina Faso. Open AIDS J 2010; 4 : 171-5. |
|33.||Spacek LA, Shihab HM, Lutwama F, Summerton J, Mayanja H, Kamya M, et al. Evaluation of a low-cost method, the Guava EasyCD4 assay, to enumerate CD4-positive lymphocyte counts in HIV-infected patients in the United States and Uganda. J Acquir Immune Defic Syndr 2006; 41 : 607-10. |
|34.||Manasa J, Musabaike H, Masimirembwa C, Burke E, Luthy R, Mudzori J. Evaluation of the Partec flow cytometer against the BD FACSCalibur system for monitoring immune responses of human immunodeficiency virus-infected patients in Zimbabwe. Clin Vaccine Immunol 2007; 14 : 293-8. |
|35.||Lynen L, Teav S, Vereecken C, De Munter P, An S, Jacques G, et al. Validation of primary CD4 gating as an affordable strategy for absolute CD4 counting in Cambodia. J Acquir Immune Defic Syndr 2006; 43 : 179-85. |
|36.||Karcher H, Böhning D, Downing R, Mashate S, Harms G. Comparison of two alternative methods for CD4+ T-cell determination (Coulter manual CD4 count and CyFlow) against standard dual platform flow cytometry in Uganda. Cytometry B Clin Cytom 2006; 70 : 163-9. |
|37.||Studio 180 and Blackfly Interactive. PointCare • Diagnostics for the People | Publications. 2007. Available from: http://www.pointcare.net/publications/, accessed on December 28, 2011. |
|38.||Sukapirom K, Onlamoon N, Thepthai C, Polsrila K, Tassaneetrithep B, Pattanapanyasat K. Performance evaluation of the Alere PIMA CD4 test for monitoring HIV-infected individuals in resource-constrained settings. J Acquir Immune Defic Syndr 2011; 58 : 141-7. |
|39.||Jani IV, Sitoe NE, Chongo PL, Alfai ER, Quevedo JI, Tobaiwa O, et al. Accurate CD4 T-cell enumeration and antiretroviral drug toxicity monitoring in primary healthcare clinics using point-of-care testing. AIDS 2011; 25 : 807-12. |
|40.||Denny TN, Gelman R, Bergeron M, Landay A, Lam L, Louzao R, et al. A North American multilaboratory study of CD4 counts using flow cytometric panLeukogating (PLG): a NIAID-DAIDS Immunology Quality Assessment Program Study. Cytometry B Clin Cytom 2008; 74 : S52-64. |
|41.||Glencross DK, Aggett HM, Stevens WS, Mandy F. African regional external quality assessment for CD4 T-cell enumeration: development, outcomes, and performance of laboratories. Cytometry B Clin Cytom 2008; 74 : S69-79. |
|42.||Glencross DK, Janossy G, Coetzee LM, Lawrie D, Aggett HM, Scott LE, et al. Large-scale affordable PanLeucogated CD4+ testing with proactive internal and external quality assessment: in support of the South African national comprehensive care, treatment and management programme for HIV and AIDS. Cytometry B Clin Cytom 2008; 74 : S40-51. |
|43.||Ceffa S, Erba F, Assane M, Coelho E, Calgaro M, Brando B. Panleucogating as an accurate and affordable flow cytometric protocol to analyse lymphocyte subsets among HIV-positive patients on HAART treatment in Mozambique. J Biol Regul Homeost Agents 2005; 19 : 169-75. |
|44.||Parra A, Reyes-Terán G, Ramírez-Peredo J, Jacquemin B, Quiroz V, Cárdenas M, et al. Differences in nocturnal basal and rhythmic prolactin secretion in untreated compared to treated HIV-infected men are associated with CD4+ T-lymphocytes. Immunol Cell Biol 2004; 82 : 24-31. |
|45.||Campbell PJ, Aurelius S, Blowes G, Harvey D. Decrease in CD4 lymphocyte counts with rest; implications for the monitoring of HIV infection. Int J STD AIDS 1997; 8 : 423-6. |
|46.||Bi X, Gatanaga H, Tanaka M, Honda M, Ida S, Kimura S, et al. Modified Dynabeads method for enumerating CD4+ T-lymphocyte count for widespread use in resource-limited situations. J Acquir Immune Defic Syndr 2005; 38 : 1-4. |
|47.||Lyamuya EF, Kagoma C, Mbena EC, Urassa WK, Pallangyo K, Mhalu FS, et al. Evaluation of the FACScount, TRAx CD4 and Dynabeads methods for CD4 lymphocyte determination. J Immunol Methods 1996; 195 : 103-12. |
|48.||Rodriguez WR, Christodoulides N, Floriano PN, Graham S, Mohanty S, Dixon M, et al. A microchip CD4 counting method for HIV monitoring in resource-poor settings. PLoS Med 2005; 2 : 663-72. |
|49.||Kantor R, Diero L, Delong A, Kamle L, Muyonga S, Mambo F, et al. Misclassification of first-line antiretroviral treatment failure based on immunological monitoring of HIV infection in resource-limited settings. Clin Infect Dis 2009; 49 : 454-62. |
|50.||Van Oosterhout JJG, Brown L, Weigel R, Kumwenda JJ, Mzinganjira D, Saukila N, et al. Diagnosis of antiretroviral therapy failure in Malawi: poor performance of clinical and immunological WHO criteria. Trop Med Int Health 2009; 14 : 856-61. |
|51.||Mellors JW, Rinaldo CR Jr, Gupta P, White RM, Todd JA, Kingsley LA. Prognosis in HIV-1 infection predicted by the quantity of virus in plasma. Science 1996; 272 : 1167-70. |
|52.||Swanson P, Huang S, Abravaya K, de Mendoza C, Soriano V, Devare SG, et al. Evaluation of performance across the dynamic range of the Abbott RealTime HIV-1 assay as compared to VERSANT HIV-1 RNA 3.0 and AMPLICOR HIV-1 MONITOR v1.5 using serial dilutions of 39 group M and O viruses. J Virol Methods 2007; 141 : 49-57. |
|53.||Triques K, Coste J, Perret JL, Segarra C, Mpoudi E, Reynes J, et al. Efficiencies of four versions of the AMPLICOR HIV-1 MONITOR test for quantification of different subtypes of human immunodeficiency virus type 1. J Clin Microbiol 1999; 37 : 110-6. |
|54.||World Health Organization. Guidelines for HIV diagnosis and monitoring of antiretroviral therapy. 2009. Available at: http://www.searo.who.int/LinkFiles/Publications_SEA-HLM-382.pdf, accessed on December 29, 2011. |
|55.||Huang D, Zhuang Y, Zhai S, Song Y, Liu Q, Zhao S, et al. HIV reverse transcriptase activity assay: a feasible surrogate for HIV viral load measurement in China. Diagn Microbiol Infect Dis 2010; 68 : 208-13. |
|56.||Stewart P, Cachafeiro A, Napravnik S, Eron JJ, Frank I, van der Horst C, et al. Performance characteristics of the Cavidi ExaVir viral load assay and the ultra-sensitive P24 assay relative to the Roche Monitor HIV-1 RNA assay. J Clin Virol 2010; 49 : 198-204. |
|57.||Labbett W, Garcia-Diaz A, Fox Z, Clewley GS, Fernandez T, Johnson M, et al. Comparative evaluation of the ExaVir Load version 3 reverse transcriptase assay for measurement of human immunodeficiency virus type 1 plasma load. J Clin Microbiol 2009; 47 : 3266-70. |
|58.||Greengrass V, Lohman B, Morris L, Plate M, Steele PM, Walson JL, et al. Assessment of the low-cost Cavidi ExaVir Load assay for monitoring HIV viral load in pediatric and adult patients. J Acquir Immune Defic Syndr 2009; 52 : 387-90. |
|59.||Iqbal HS, Balakrishnan P, Cecelia AJ, Solomon S, Kumarasamy N, Madhavan V, et al. Use of an HIV-1 reverse-transcriptase enzyme-activity assay to measure HIV-1 viral load as a potential alternative to nucleic acid-based assay for monitoring antiretroviral therapy in resource-limited settings. J Med Microbiol 2007; 56 : 1611-4. |
|60.||Schüpbach J, Böni J. Quantitative and sensitive detection of immune-complexed and free HIV antigen after boiling of serum. J Virol Methods 1993; 43 : 247-56. |
|61.||Schüpbach J, Flepp M, Pontelli D, Tomasik Z, Lüthy R, Böni J. Heat-mediated immune complex dissociation and enzyme-linked immunosorbent assay signal amplification render p24 antigen detection in plasma as sensitive as HIV-1 RNA detection by polymerase chain reaction. AIDS 1996; 10 : 1085-90. |
|62.||Böni J, Opravil M, Tomasik Z, Rothen M, Bisset L, Grob PJ, et al. Simple monitoring of antiretroviral therapy with a signal-amplification-boosted HIV-1 p24 antigen assay with heat-denatured plasma. AIDS 1997; 11 : F47-52. |
|63.||Rouet F, Ménan H, Viljoen J, Ngo-Giang-Huong N, Mandaliya K, Valéa D, et al. In-house HIV-1 RNA real-time RT-PCR assays: principle, available tests and usefulness in developing countries. Expert Rev Mol Diagn 2008; 8 : 635-50. |
|64.||Mine M, Bedi K, Maruta T, Madziva D, Tau M, Zana T, et al. Quantitation of human immunodeficiency virus type 1 viral load in plasma using reverse transcriptase activity assay at a district hospital laboratory in Botswana: a decentralization pilot study. J Virol Methods 2009; 159 : 93-7. |
|65.||Tehe A, Maurice C, Hanson DL, Hanson b, Marie Y, Borget a,0 et al. Quantification of HIV-1 p24 by a highly improved ELISA: an alternative to HIV-1 RNA based treatment monitoring in patients from Abidjan, Côte d'Ivoire. J Clin Virol 2006; 37 : 199-205. |
|66.||Prado JG, Shintani A, Bofill M, Clotet B, Ruiz L, Martinez-Picado J. Lack of longitudinal intrapatient correlation between p24 antigenemia and levels of human immunodeficiency virus (HIV) Type 1 RNA in patients with chronic hiv infection during structured treatment interruptions. J Clin Microbiol 2004; 42 : 1620-5. |
|67.||Pascual A, Cachafeiro A, Funk ML, Fiscus SA. Comparison of an assay using signal amplification of the heat-dissociated p24 antigen with the Roche Monitor human immunodeficiency virus RNA assay. J Clin Microbiol 2002; 40 : 2472-5. |
|68.||Lombart JP, Vray M, Kafando A, Lemée V, Ouédraogo-Traoré R, Corrigan GE, et al. Plasma virion reverse transcriptase activity and heat dissociation-boosted p24 assay for HIV load in Burkina Faso, West Africa. AIDS 2005; 19 : 1273-7. |
|69.||Amellal B, Katlama C, Calvez V. Evaluation of the use of dried spots and of different storage conditions of plasma for HIV-1 RNA quantification. HIV Med 2007; 8 : 396-400. |
|70.||Ayele W, Schuurman R, Messele T, Dorigo-Zetsma W, Mengistu Y, Goudsmit J, et al. Use of dried spots of whole blood, plasma, and mother's milk collected on filter paper for measurement of human immunodeficiency virus type 1 burden. J Clin Microbiol 2007; 45 : 891-6. |
|71.||Brambilla D, Jennings C, Aldrovandi G, Bremer J, Comeau AM, Cassol SA, et al. Multicenter evaluation of use of dried blood and plasma spot specimens in quantitative assays for human immunodeficiency virus RNA: measurement, precision, and RNA stability. J Clin Microbiol 2003; 41 : 1888-93. |
|72.||Mehta N, Trzmielina S, Nonyane BA, Eliot MN, Lin R, Foulkes AS, et al. Low-cost HIV-1 diagnosis and quantification in dried blood spots by real time PCR. PLoS One 2009; 4 : e5819. |
|73.||Gilks C, Vitória M. Antiretroviral therapy for HIV infection in adults and adolescents: recommendations for a public health approach. HIV/AIDS Programme - World Health Organization. WHO, Geneva: World Health Organization; 2006. Available from: www.who.int/hiv/pub/guidelines/artadultguidelines.pdf, accessed on September 22, 2011. |
|74.||May S, Gamst A, Haubrich R, Benson C, Smith DM. Pooled nucleic acid testing to identify antiretroviral treatment failure during HIV infection. J Acquir Immune Defic Syndr 2010; 53 : 194-201. |
|75.||Tilghman MW, Guerena DD, Licea A, Pérez-Santiago J, Richman DD, May S, et al. Pooled nucleic acid testing to detect antiretroviral treatment failure in Mexico. J Acquir Immune Defic Syndr 2011; 56 : e70-4. |
|76.||Lloyd RM Jr, Burns DA, Huong JT, Mathis RL, Winters MA, Tanner M, et al. Dried-plasma transport using a novel matrix and collection system for human immunodeficiency virus and hepatitis C virus virologic testing. J Clin Microbiol 2009; 47 : 1491-6. |
|77.||Napravnik S, Cachafeiro A, Stewart P, Eron JJ Jr, Fiscus SA. HIV-1 viral load and phenotypic antiretroviral drug resistance assays based on reverse transcriptase activity in comparison to amplification based HIV-1 RNA and genotypic assays. J Clin Virol 2010; 47 : 18-22. |
|78.||Greengrass VL, Plate MM, Steele PM, Denholm JT, Cherry CL, Morris LM, et al. Evaluation of the Cavidi ExaVir Load assay (version 3) for plasma human immunodeficiency virus type 1 load monitoring. J Clin Microbiol 2009; 47 : 3011-3. |
|79.||Malmsten A, Shao X-W, Sjödahl S, Fredriksson E-L, Pettersson I, Leitner T, et al. Improved HIV-1 viral load determination based on reverse transcriptase activity recovered from human plasma. J Med Virol 2005; 76 : 291-6. |
|80.||Greengrass VL, Turnbull SP, Hocking J, Dunne AL, Tachedjian G, Corrigan GE, et al. Evaluation of a low cost reverse transcriptase assay for plasma HIV-1 viral load monitoring. Curr HIV Res 2005; 3 : 183-90. |
|81.||Stevens G, Rekhviashvili N, Scott LE, Gonin R, Stevens W. Evaluation of two commercially available, inexpensive alternative assays used for assessing viral load in a cohort of human immunodeficiency virus type 1 subtype C-infected patients from South Africa. J Clin Microbiol 2005; 43 : 857-61.Malmsten A, Shao X-W, Aperia K, Corrigan GE, Sandström E, Källander CFR, et al. HIV-1 viral load determination based on reverse transcriptase activity recovered from human plasma. J Med Virol 2003; 71 : 347-59. |
[Table 1], [Table 2], [Table 3], [Table 4]
|This article has been cited by|
||Super RLuc8-sFv; a new luciferase-labeled probe for detection of human CD4+ cells
| ||A. Safavi,R. Emamzadeh,M. Nazari,M. Ehsani,S. H. Zarkesh-Esfahani,S. Rahgozar |
| ||Mol. BioSyst.. 2017; |
|[Pubmed] | [DOI]|
||Using BD Vacutainer CD4 Stabilization Tubes for Absolute Cluster of Differentiation Type 4 Cell Count Measurement on BD FacsCount and Partec Cyflow Cytometers: A Method Comparison Study from Zimbabwe
| ||Florian Vogt,Rafael Van den Bergh,Andrea Bernasconi,Buhlebenkosi Moyo,Liberty Havazvidi,Mathieu Bastard,Laurence Flevaud,Fabian Taziwa,Eliphas Makondo,Sekesai Mtapuri-Zinyowera,Bruno Verhasselt |
| ||PLOS ONE. 2015; 10(8): e0136537 |
|[Pubmed] | [DOI]|
||Point-of-Care CD4 Testing to Inform Selection of Antiretroviral Medications in South African Antenatal Clinics: A Cost-Effectiveness Analysis
| ||Andrea L. Ciaranello,Landon Myer,Kathleen Kelly,Sarah Christensen,Kristen Daskilewicz,Katie Doherty,Linda-Gail Bekker,Taige Hou,Robin Wood,Jordan A. Francke,Kara Wools-Kaloustian,Kenneth A. Freedberg,Rochelle P. Walensky,Ravi Jhaveri |
| ||PLOS ONE. 2015; 10(3): e0117751 |
|[Pubmed] | [DOI]|
||Comparison of Swarm Intelligence Techniques for Estimation of HIV-1 Viral Load
| ||Krishnamurthy Kamalanand,Ponnuswamy Mannar Jawahar |
| ||IETE Technical Review. 2015; : 1 |
|[Pubmed] | [DOI]|
||Printed Flexible Plastic Microchip for Viral Load Measurement through Quantitative Detection of Viruses in Plasma and Saliva
| ||Hadi Shafiee,Manoj Kumar Kanakasabapathy,Franceline Juillard,Mert Keser,Magesh Sadasivam,Mehmet Yuksekkaya,Emily Hanhauser,Timothy J. Henrich,Daniel R. Kuritzkes,Kenneth M. Kaye,Utkan Demirci |
| ||Scientific Reports. 2015; 5: 9919 |
|[Pubmed] | [DOI]|
||The performance of reverse transcriptase assay for the estimation of the plasma viral load in HIV-1 and HIV-2 infections
| ||Priyadarshini A. Padaki,Jaiprasath Sachithanandham,Rita Isaac,Veena V. Ramalingam,Ooriapadickal C. Abraham,Susanne A. Pulimood,Rajesh Kannangai |
| ||Infectious Diseases. 2015; : 1 |
|[Pubmed] | [DOI]|
||Molecular HIV screening
| ||Thomas Bourlet,Meriam Memmi,Henia Saoudin,Bruno Pozzetto |
| ||Expert Review of Molecular Diagnostics. 2013; 13(7): 693 |
|[Pubmed] | [DOI]|
||Rapid, effective and user-friendly immunophenotyping of canine lymphoma using a personal flow cytometer
| ||Stratos Papakonstantinou,Inese Berzina,Amanda Lawlor,Emma J O’Neill,Peter J O’Brien |
| ||Irish Veterinary Journal. 2013; 66(1): 6 |
|[Pubmed] | [DOI]|
||Comparative evaluation of the Abbott HIV-1 RealTime™ assay with the Standard Roche COBAS® Amplicor™ HIV-1 Monitor® Test, v1.5 for determining HIV-1 RNA levels in plasma specimens from Pune, India
| ||Priyanka Khopkar,Vikas Mallav,Shweta Chidrawar,Smita Kulkarni |
| ||Journal of Virological Methods. 2013; 191(1): 82 |
|[Pubmed] | [DOI]|
||HIV in the tropics
| ||Julie K. Varughese,Michael G. Rosenberg,Kami Kim |
| ||Current Opinion in Infectious Diseases. 2012; 25(5): 477 |
|[Pubmed] | [DOI]|