Glycemic Control in the 12 Months following a Change to SI Hemoglobin A1c Reporting Units

Abstract

Many countries have implemented, or are considering, a change in hemoglobin A1c (Hb A1c) units from traditional percentage values [Diabetes Control and Complications Trial (DCCT)] to the new Système International d'Unités (SI) unit in millimoles per mole. Concern exists that such a large alteration in numeric values might lead, through confusion, to a deterioration in patients' glycemia. This study has assessed Hb A1c in the year before and after the change of units in a UK diabetes population. The Hb A1c in the 12 months immediately before the unit change (October 2010 to September 2011) was compared with the 12 months after (October 2011 to September 2012). Also, the subsequent change in Hb A1c in patients who had poor glycemic control [Hb A1c >8% (64 mmol/mol)], either before or after the unit change, was compared. Over the 2 years, 44 721 Hb A1c measurements were requested on 13,197 (7247 male, 5950 female) known diabetes patients. The population Hb A1c was no different between years, with a median [interquartile range (IQR)] value of 7.5% (6.6%-8.7%) after the change and 7.5% (6.5-8.7) before (P = 0.34). The subsequent change in Hb A1c following a raised (>8%) result was the same regardless of whether the initial value reported was in DCCT or SI units [median (IQR) change in Hb A1c -0.2% (-0.9% to 0.3%), n = 4316, following a DCCT result, vs -0.2% (-0.8% to 0.3%), n = 4396, following SI; P = 0.44]. In this UK diabetes population, a move to SI Hb A1c reporting did not lead to any marked short-term deterioration in glycemia or a different Hb A1c outcome in patients with initial poor glucose control.