Validation of an algorithm combining haemoglobin A _1c and fasting plasma glucose for diagnosis of diabetes mellitus in UK and Australian populations

Manley, S.E., Sikaris, K.A., Lu, Z.X., Nightingale, P.G., Stratton, I.M., Round, R.A., Baskar, V., Gough, S.C.L. and Smith, J.M. (2009) Validation of an algorithm combining haemoglobin A _1c and fasting plasma glucose for diagnosis of diabetes mellitus in UK and Australian populations. Diabetic Medicine, 26 (2), 115-121. (doi:10.1111/j.1464-5491.2008.02652.x).

Abstract

Aim: to determine whether glycated haemoglobin (HbA _1c) can be used in combination with fasting plasma glucose (FPG) for the diagnosis of diabetes in patients with impaired fasting glucose (IFG) and in a broader spectrum of patients. 

Methods: an algorithm was derived from oral glucose tolerance test (OGTT) capillary samples in 500 consecutive UK patients with IFG by World Health Organization criteria. It was validated in a further 500 UK patients and, with venous specimens, in 1175 unselected Australian patients. 

Results: the derivation cohort was aged 61 years (50-69 years) (median IQ range) with 52% male and 12% South Asian. Diabetes Control and Complications Trial-aligned HbA _1c was 6.2% (5.8-6.6%) (reference interval < 6.0%) and FPG 6.7 mmol/l (6.3-7.2 mmol/l). FPG was in the diabetes range in 36% of patients, with an OGTT identifying a further 12% with diabetes. The derived algorithm, (HbA _1c ≥ 6.0% with FPG < 7.0 mmol/l) identified those patients requiring an OGTT to diagnose diabetes. When applied to the UK validation cohort, sensitivity was 97% and specificity 100%. The algorithm was equally effective in the unselected group, aged 59 years (49-68 years) and 54% male, with sensitivity 93% and specificity 100%. HbA _1c was 6.0% (5.6-6.6%) and FPG 6.0 mmol/l (5.3-6.8 mmol/l), with 26% having IFG. Use of the algorithm would reduce the number of OGTTs performed in the UK validation cohort by 33% and by 66% in the Australian patients studied. 

Conclusions: use of this algorithm would simplify procedures for diagnosis of diabetes and could also be used for monitoring pre-diabetes. Validation is now required in other populations and patient groups.

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Contributors

Author: I.M. Stratton

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