ASSESSING GLYCEMIC CONTROL IN DIABETES - RELATIONSHIPS BETWEEN FRUCTOSAMINE AND HBA(1C)

Aim. Glycated haemoglobin (HbA(1C)) has become the internationally est ablished method of assessing long term glycaemic control in people wit h diabetes. In New Zealand the measurement of glycated albumin (fructo samine), which is substantially cheaper than HbA(1C) has been widely a dopted. In this study we have sought to determine if the value of HbA( 1C) can be reliably estimated from knowledge of plasma fructosamine. M ethods. Fifty subjects with diabetes and stable glycaemic control as a ssessed by 3-5 simultaneous measurements of HbA(1C) and fructosamine m ade sequentially over a median of 6 months, were studied. The relation ship between the two measures was assessed by determining 95% predicti on intervals for HbA(1C) from the regression equation relating mean Hb A(1C), and fructosamine. A further 8 subjects with significantly chang ing glycaemic control were also studied. Results. Mean stable plasma f ructosamine and HbA(1C) measurements were closely correlated (r=0.661, p<0.0001) with HbA(1C) increasing on average 1% for every 56 mu mol L -1 increase in fructosamine. The prediction intervals for HbA(1C) were however wide. Thus at a plasma fructosamine of 350 mu mol L-1 the 95% prediction intervals for HbA(1C) ranged from 6.6 to 11.2% (3 to 11 st andard deviations above the mean of the normal reference range). This variability could not be accounted for by the presence of albuminuria or by the exclusion of those subjects with the greatest variability in fructosamine. In the subjects showing changes in glycaemic control, a change in HbA(1C) of 1% was associated with a change in fructosamine of between 29 and 63 mu mol L-1. Conclusions. Fructosamine levels gene rally correlate well with HbA(1C), within a population but the value o f HbA(1C) in an individual cannot be inferred with any reliability fro m the level of fructosamine, nor can the change in HbA(1C) be inferred from the change in fructosamine. We suggest that if fructosamine is t o be used as an index of glycaemic control in diabetes, it is suppleme nted by a measurement of HbA(1C) when fructosamine measurements are st able, in order to determine whether the given value of fructosamine is consistent with the glycaemic control targets for that individual.