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ORIGINAL ARTICLE
Year : 2016  |  Volume : 144  |  Issue : 2  |  Page : 220-228

Derivation & validation of glycosylated haemoglobin (HbA 1c ) cut-off value as a diagnostic test for type 2 diabetes in south Indian population


1 Department of Medicine, Sri Venkateswara Institute of Medical Sciences, Tirupati, India
2 Department of Endocrinology and Metabolism, Sri Venkateswara Institute of Medical Sciences, Tirupati, India
3 Department of Statistics, Sri Venkateswara University, Tirupati, India
4 Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, India
5 Department of Biochemistry, Sri Venkateswara Institute of Medical Sciences, Tirupati, India
6 Department of General Medicine, Harshitha Hospital, Tirupati, India

Correspondence Address:
Alladi Mohan
Department of Medicine, Sri Venkateswara Institute of Medical Sciences, Tirupati 517 507, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-5916.195035

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Background & Objectives: Glycosylated haemoglobin (HbA 1c ) has been in use for more than a decade, as a diagnostic test for type 2 diabetes. Validity of HbA 1c needs to be established in the ethnic population in which it is intended to be used. The objective of this study was to derive and validate a HbA 1c cut-off value for the diagnosis of type 2 diabetes in the ethnic population of Rayalaseema area of south India. Methods: In this cross-sectional study, consecutive patients suspected to have type 2 diabetes underwent fasting plasma glucose (FPG) and 2 h post-load plasma glucose (2 h-PG) measurements after a 75 g glucose load and HbA 1c estimation. They were classified as having diabetes as per the American Diabetes Association criteria [(FPG ≥7 mmol/l (≥126 mg/dl) and/or 2 h-PG ≥11.1 mmol/l (≥200 mg/dl)]. In the training data set (n = 342), optimum cut-off value of HbA 1c for defining type 2 diabetes was derived by receiver-operator characteristic (ROC) curve method using oral glucose tolerance test results as gold standard. This cut-off was validated in a validation data set (n = 341). Results: On applying HbA 1c cut-off value of >6.3 per cent (45 mmol/mol) to the training data set,sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for diagnosing type 2 diabetes were calculated to be 90.6, 85.2, 80.8 and 93.0 per cent, respectively. When the same cut-off value was applied to the validation data set, sensitivity, specificity, PPV and NPV were 88.8 , 81.9, 74.0 and 92.7 per cent, respectively, although the latter were consistently smaller than the proportions for the training data set, the differences being not significant. Interpretation & conclusions: HbA 1c >6.3 per cent (45 mmol/mol) appears to be the optimal cut-off value for the diagnosis of type 2 diabetes applicable to the ethnic population of Rayalaseema area of Andhra Pradesh state in south India.


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