The effect of the new ADA and WHO guidelines on the number of diagnosed cases of diabetes mellitus

In the new lowered diagnostic discriminator for diabetes mellitus (DM) from the American Diabetes Association (ADA), fasting peripheral venous plasma glucose (fvPG) of 7.0 mmol/l is identical to the 99.9 centile of fvPG (7.05 mmol/l, 95%CI: 6.917.20 mmol/l) in a lowrisk reference population. We investigated its diagnostic concordance with other diagnostic discriminators. As no index test is available for DM we used the ADA discriminator as gold standard. We isolated a lowrisk reference population (n = 424) from a randomised general population (n = 726) by ruling out of all cases with clinical and biochemical risk indicators for DM. We based our analysis on measurements traceable to primary standard concentration, a bias of <1.5% and CV% < 2.5. The distribution of the fasting capillary whole blood glucose (fCBG; mmol/l) in the reference population was ln Gaussian with the 99.9 centile of 6.62 mmol/l (95% CI 6.476.77 mmol/l) and the 97.5 centile of 5.92 mmol/l (5.826.02 mmol/l). The 6.1 mmol/l fCBG WHO limit corresponds approximately to the 97.6 centile, and this limit is thus not traceable to the ADA discriminator, which corresponds to fCBG of 6.4 mmol/l. This is the case in groups only, as recalculation will introduce unpredictable errors. Thus, in our general population a varying number of subjects will be at risk of DM as a mere consequence of different limits. The fCBG limit of 6.1 mmol/l will thus lead to 2.4% falsepositive diagnoses or, in EU, to around 44 x 10(6) adults being diagnosed. The number of cases at risk of DM vary from 5.4 x 10(6) to 44 x 10(6) in EU. We conclude that application of different diagnostic limits results in highly variable number of diagnosed DM cases, and therefore one diagnostic discriminator is needed to provide reproducible diagnoses.