Can HbA_1c 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 to 2007, 2061 white Caucasians, aged >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 HbA_1c in representative subgroup (n = 148). Comparable data were obtained for 108 primary care patients at risk of diabetes. Results: Diabetes was diagnosed immediately by routine practice in 1% (22/2061) [aged 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 HbA_1c similar to primary care patients [54 (46–61) years], 5.7 (5.3–6.0)%/39 (34–42) mmol/mol (n = 148) vs 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) vs 5.2 (4.8–5.9) mmol/L, p = 0.65, but 2hPG higher, 9.0 (7.3–11.4) vs 5.5 (4.4–7.5), p < 0.001. HbA_1c identified diabetes in 10% (15/148) with 14 confirmed on OGTT but overall 32% (48/148) were in diabetic range on OGTT. The specificity of HbA_1c in 2061 admissions was similar to primary care, 99% vs 96%, p = 0.20, but sensitivity lower, 38% vs 93%, p < 0.001 (63% on FPG/23% on 2hPG, p = 0.037, in those with possible symptoms/complications). Conclusion: HbA_1c 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 resulting from the acute medical event.