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Haemoglobin A1c (A1c) levels are lower during haemolysis because of the shorter exposure of haemoglobin (Hb) to plasma glucose. Ribavirin (RBV) used in combination with interferon-alpha (IFN) for chronic hepatitis C causes reversible haemolytic anaemia. This study examined the extent to which RBV treatment influences A1c levels in diabetic patients. A retrospective analysis identified 32 diabetic patients who underwent hepatitis C treatment with IFN and RBV. Each subject had at least three measures of A1c, Hb and glucose: before, during and after therapy. A1c values decreased from a mean pretreatment level of 7.2% to an on-treatment A1c level of 5.2% [mean paired difference -2.01%; 95% confidence interval (CI) -1.59% to -2.43%; P < 0.001]. During therapy, mean Hb levels decreased from 15.1 g/dL at baseline to a nadir of 11.7 g/dL (P < 0.001) with a rise in lactose dehydrogenase levels and reticulocyte counts, and unchanged mean corpuscular volume values confirming haemolysis. At the same time, glucose levels declined by a mean of 38.4 mg/dL (95% CI 13.4-63.5 mg/dL; P = 0.002) as did body weights by a mean of 3.15 kg (P < 0.001). According to published glucose-A1c correlation tables, this decline of glucose concentration by 38.4 mg/dL correlates to a decline in A1c level of 1.08%. In conclusion, reductions of A1c levels by a mean of 2.01% during hepatitis C therapy with IFN + RBV are due to a combination of decreased glucose levels (1.08%) and RBV-induced haemolysis (0.93%). A1c levels should not be measured during hepatitis C treatment with IFN + RBV because they do not adequately reflect glycaemic control.

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