Can HbA1c detect undiagnosed diabetes in acute medical hospital admissions?

OBJECTIVE: To study hyperglycaemia in acute medical admissions to Irish regional hospital.RESEARCH DESIGN AND METHODS—From 2005-2007, 2061 White Caucasians, >18 years, were admitted by 1/7 physicians. Those with diabetes symptoms/complications but no previous record of hyperglycaemia (n = 390), underwent OGTT with concurrent HbA1c in representative subgroup (n = 148). Comparable data was obtained for 108 primary care patients at risk of diabetes.
RESULTS: Diabetes was diagnosed immediately by routine practice in 1% (22/2061) [age 36(26-61) years (median IQ range)/55% (12/22) male with pre-existing diabetes/dysglycaemia present in 19% (390/2061) [69(58-80) years/60% (235/390) male].Possible diabetes symptoms/complications were identified in 19% [70(59-79) years/57% (223/390) male] with their HbA1c similar to primary care patients [54(46-61) years],5.7(5.3-6.0)%/39(34-42) mmol/mol (n = 148) v 5.7(5.4-6.1) %/39(36-43) mmol/mol, p =0.35, but lower than those diagnosed on admission, 10.2(7.4-13.3)%/88(57-122) mmol/mol, p < 0.001.Their fasting plasma glucose (FPG) was similar to primary care patients, 5.2(4.8-5.7) v 5.2(4.8-5.9) mmol/L, p = 0.65, but 2hPG higher, 9.0(7.3-11.4) v 5.5(4.4-7.5), p < 0.001.HbA1c identified diabetes in 10% (15/148) with 14 confirmed on OGTT but overall 32% (48/148) in diabetic range on OGTT.The specificity of HbA1c in 2061 admissions was similar to primary care, 99% v 96%, p = 0.20, but sensitivity lower, 38% v 93%, p <0.001 (63% on FPG/23% on 2hPG, p = 0.037, in those with possible symptoms/complications).
CONCLUSION: HbA1c can play a diagnostic role in acute medicine as it diagnosed another 2% of admissions with diabetes but the discrepancy in sensitivity shows that it does not reflect transient/acute hyperglycaemia from the acute medical event.