In the new lowered diagnostic discriminator for diabetes mellitus (DM) from the American Diabetes Association (ADA), fasting peripheral venous plasma glucose (f-vPG) of 7.0 mmol/l is identical to the 99.9 centile of f-vPG (7.05 mmol/l, 95%CI: 6.91–7.20 mmol/l) in a low-risk 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 low-risk 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 (f-CBG; mmol/l) in the reference population was ln Gaussian with the 99.9 centile of 6.62 mmol/l (95% CI 6.47–6.77 mmol/l) and the 97.5 centile of 5.92 mmol/l (5.82–6.02 mmol/l). The 6.1 mmol/l f-CBG WHO limit corresponds approximately to the 97.6 centile, and this limit is thus not traceable to the ADA discriminator, which corresponds to f-CBG 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 f-CBG limit of 6.1 mmol/l will thus lead to 2.4% false-positive diagnoses or, in EU, to around 44 × 106 adults being diagnosed. The number of cases at risk of DM vary from 5.4 × 106 to 44 × 106 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.
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