Intra-individual variability and longitudinal changes in glycaemic controlin patients with Type 1 diabetes mellitus

Aims Patients with Type 1 diabetes mellitus (DM) appear to have remarkably stable HbA(1c) levels, regardless of the need for improvement. The purpose of the present study was therefore to study predictors of intra-individual variability of the HbA(1c) level together with changes in HbA(1c) over time . Methods Hospital records of patients with Type 1 DM seen at our diabetes cl inic from February 1992 to May 1997 were reviewed for HbA(1c) measurements and clinical data. In the main study, 214 patients who had been on insulin for more than 1 year, and in a sub-study, 14 patients newly started on insu lin, were included. Results The coefficient of variation (CV) of the intra-individual HbA(1c) m easurements, after at least 1 year of insulin, was 8.8 +/- 3.7% (mean +/- s d). There was a positive association between the CV and the HbA(1c) measure ment at inclusion in the study (P < 0.05), and also a negative association between the CV and age (P < 0.05). Fifty per cent of the patients had a dif ference between first and last HbA(1c) below 1%, and 83.6% had a difference below 2%. In the sub-study, there was a positive association between the m ean HbA(1c) value the first year on insulin (excluding the first 3 months) and the last HbA(1c) measurement (P < 0.01). Conclusions The HbA(1c) levels in individual patients remain remarkably sta ble over time. Furthermore, the HbA(1c) level shortly after starting insuli n is a predictor of future glycaemic control.