Assessing the impact of blood sample type on the estimated prevalence of impaired glucose tolerance and diabetes mellitus in epidemiological surveys.

In a prospective study of 353 patients who had undergone coronary artery bypass graft surgery a 75 g oral glucose tolerance test was performed at 3 months and 12 months after surgery. Venous whole blood glucose and venous plasma glucose samples were assayed on a bench-top analyser. The World Health Organization diagnostic criteria for impaired glucose tolerance and diabetes mellitus were applied to venous whole blood glucose and venous plasma glucose measurements. The difference between the plasma and whole blood concentration of glucose was 0.79-0.86 mmol l-1 at a plasma glucose of 7.8 mmol l-1 and 1.22-1.24 mmol l-1 at a plasma glucose of 11.1 mmol l-1 (compared to 1.1 mmol l-1 by World Health Organization criteria at both cut-points). Despite this, in our subject population with a high prevalence of impaired glucose tolerance (20.3% at 3 months, 15.3% at 12 months) and diabetes mellitus (10.1% at 3 months and 12 months), there was no significant difference in the proportion classified impaired glucose tolerance or having diabetes mellitus using venous whole blood glucose compared to venous plasma glucose. We conclude that despite the minor anomaly between WHO diagnostic criteria based on venous whole blood glucose and venous plasma glucose measurements, these criteria are robust and give broadly comparable population prevalence of diabetes mellitus and impaired glucose tolerance irrespective of blood sample choice.