Introduction: In 2011 the diagnostic criteria for diabetes in Denmark was changed from an oral glucose tolerance test (OGTT) to HbA1c. Several studies have shown that the OGTT identifies diabetes at a lower HbA1c level than the current threshold. Several countries have seen a decreasing type 2 diabetes incidence after 2011, possibly related to new diagnostic criteria. It is therefore conceivable that the HbA1c level at the time of diagnosis should be increasing after 2011. We investigated the level of HbA1c in newly diagnosed type2 diabetes patients in Denmark in the period 2010-16, to test this conjecture.
Methods: We obtained HbA1c measurements from the national laboratory database which contains person-identifiable laboratory measurements on all Danish citizens. These were linked to a national register on all type 2 diabetes patients, which was based on national health care registers. We chose the HbA1c measurement closest to the date of diabetes, but only in a window from 3 months before to 1 month after diagnosis.
Results: Information on HbA1c was available for 98,010 out of 132,534 persons with type 2 diabetes registered in the period 2010-16 incl. The overall level of HbA1c was stable in the period 2010-13, but from 2013 we saw weak increase in the median HbA1c at diagnosis, most pronounced for men (48 to 56 mmol/mol) compared to women (47 to 52 mmol/mol). But the 90th percentile of HbA1c increased in the period 2013-16 for men from 78 to 101 and for women from 65 to 88 mmol/mol, while percentiles of HbA1c below the median were stable.
Conclusion: HbA1c at diagnosis increased in the period 2013-16, presumably because the diagnosis is made at a more advanced state when using HbA1c as criterion as compared to OGTT. In the same period the incidence rates of type 2 diabetes was increasing to 2011, then declining till 2015 and after that increased again. Future studies will show whether changes in HbA1c levels influences the prevalence, incidence and mortality of persons included as diabetes patients in the register.
B. Carstensen: Consultant; Self; Leo Pharma. Speaker's Bureau; Self; Novo Nordisk A/S. Stock/Shareholder; Self; Novo Nordisk Inc. P.F. Rønn: Research Support; Self; Amgen AB. Stock/Shareholder; Spouse/Partner; Novo Nordisk A/S. M.E. Jørgensen: Research Support; Self; Amgen Inc., AstraZeneca, Danish Diabetes Association, Sanofi-Aventis. Stock/Shareholder; Self; Novo Nordisk A/S.