HbA1C measured by a colorimetric method in normal and diabetic Nigerian subjects

Glycosylation of haemoglobin was evaluated in 30 normal adult Nigerians and 60 diabetic adult Nigerians who were at various stages of blood glucose control, by measuring ketoamine-linked hexoses in haemoglobin. These hexoses were converted by digestion with 1 M oxalic acid for 4.5 h at 100 degrees C to 5-hydroxymethylfurfural, which was measured by reaction with 2 thiobarbituric acid. Glycosylation of haemoglobin was expressed as micromoles (mumol) of fructose per 5% haemoglobin. A mean fructose concentration of 91.0 mumol/1 (s.d. +/- 9.3) was obtained for normal subjects; that for diabetic adult Nigerians was 175.3 mumol/l (s.d. +/- 26.4). There was significant correlation between fasting blood glucose levels and glycosylated haemoglobins in both normal adults (r = 0.77, P less than 0.001) and diabetic adults (r = 0.90, P less than 0.001). The colorimetric method was found to be precise and accurate with an interassay variability of 1.44% and an intra-assay variability of 0.98%.