Competitive Insulin Autoantibody Assay: Prospective Evaluation of Subjects at High Risk for Development of Type I Diabetes Mellitus

Abstract

A quantitative fluid-phase radioassay for autoantibodies reacting with insulin (competitive insulin autoantibody assay, CIAA) was developed. The assay's features include 1) use of a physiologic amount of 125I-labeled insulin, 2) parallel incubations with supraphysiologic cold insulin (competitive), and 3) an incubation time of 7 days and a single-step multiple-wash polyethylene glycol separation. Mean +/- SE CIAA levels in 50 controls were 8 +/- 1.4 nU/ml (range -16-33.3). In 36 cytoplasmic islet cell antibody (ICA)-positive nondiabetic first-degree relatives of type I (insulin-dependent) patients less than 30 yr of age, CIAA levels exceeded the normal range in 20 (55.6%) of 36 (mean 86.8 +/- 17.1 nU/ml). In 26 ICA-positive relatives greater than 30 yr of age, only 5 (19.2%) of 26 exceeded the normal range (mean 26.1 +/- 9.4 nU/ml); P less than .001 compared with younger ICA-positive relatives). Six ICA-negative HLA-identical siblings of type I diabetic patients had normal CIAA levels (mean 3.6 +/- 5.8 nU/ml), and only 2 of 13 ICA-negative identical twins discordant for diabetes (mean 15.4 +/- 6.6 nU/ml) exceeded the normal range. Nine (50%) of 18 ICA-positive schoolchildren exceeded the normal range (mean 105.3 +/- 36.7 nU/ml). Genetically susceptible subjects negative for CIAA (with only 3 exceptions) remained negative for CIAA on multiple determinations (3 conversions observed), and CIAA levels of positive subjects were relatively stable. Linear regression of the first CIAA level versus last (interval between sampling 1 mo to 10 yr) in genetically susceptible individuals showed a highly significant correlation (r = .95, P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Karlsburg Type I diabetes risk study of a general population: frequencies and interactions of the four major Type I diabetes-associated autoantibodies studied in 9419 schoolchildren

“…IAA were detected according Vardi et al [18,19] with a slight modification. Fifty ml (25 000 cpm) of 0.1 nmol/l A14 mono-125I-human insulin (specific activity 360 mCi/mg, a kind gift of Hoechst, Frankfurt, Germany) were incubated with 50 ml serum in duplicates for 3 days at 4°C with and without 333 nmol/l unlabelled human insulin to display the specific 125I-insulin binding.…”

Antibodies to the Mr 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired Beta-cell function

“…CIAA were detected by the competitive radiobinding assay described by Vardi et al [18]. A total binding insulin level above 45 nU/ml (mean + 3 SD of 100 control subjects) was regarded as positive.…”

Type 1 diabetes islet associated antibodies in subjects infected by echovirus 16

“…Insulin autoantibodies were detected using a competitive fluid-phase radioimmunoassay [27]. In the Fourth International Diabetes Workshop IAA proficiency test program held in 1994, University of Florida, our laboratory (lab 232, Havana, Cuba) obtained 100% specificity and 43% sensitivity.…”