Insulin autoantibodies in first degree relatives of type I diabetic patients

1. Insulin autoantibodies (IAA) of first-degree relatives of type I diabetic patients and recent-onset type I diabetics were measured by radioimmunoassay. A cut-off of 60 nU/ml was established on the basis of the values of normal control individuals. The intra-assay coefficient of variation was 9.2% for a moderately positive serum (1908 +/- 176 nU/ml (mean +/- SD), N = 7; range, 1708 to 2158 nU/ml). The interassay coefficient of variation was 23.8% for a negative (normal control) serum (28.1 +/- 6.7 nU/ml, N = 6; range, 22 to 39 nU/ml) and 14.5% in a highly positive serum (6185 +/- 899 nU/ml, N = 7; range, 5053 to 7009 nU/ml). 2. Insulin autoantibody levels (mean +/- SEM) were 19.3 +/- 2.8 nU/ml (range, -19 to 40 nU/ml) in 25 controls, 24.8 +/- 3.4 nU/ml (range, -17 to 59 nU/ml) in 41 type II diabetic patients, 18.5 +/- 2.4 nU/ml (range, -58 to 268 nU/ml) in 171 first-degree relatives of type I diabetic patients and 208.9 +/- 87.0 nU/ml (range, 10 to 1101 nU/ml) in 16 recent-onset type I diabetic patients. IAA levels were significantly higher in the last group compared with the other groups (P < 0.01). 3. None of the controls or type II diabetics exceeded the upper limit of normality. In contrast, 9 of 171 (5.3%) first-degree relatives and 9 of 16 (56.0%) recent-onset type I diabetic patients had IAA levels above the 60 nU/ml cut-off point.(ABSTRACT TRUNCATED AT 250 WORDS)