Glucagon Radioimmunoassay Using Antiserum 30K: Interference by Plasma

Studies of a glucagon radioimmunoassay using antiserum 30K suggest that when plasma samples from different individuals are assayed against a single standard curve, an inappropriately wide range of values for fasting human pancreatic glucagon levels is obtained. Evidence is presented that plasma from different subjects contains non-specific factors which interfere with the assay. These factors depress the binding of labeled glucagon but appear to be neither pancreatic glucagon nor an enteric factor with glucagon-like immunoreactivity. A correction can be made for these interference factors in a given patient because the factors can be quantitated following adsorption of glucagon with charcoal. Fasting immunoreactive glucagon (IRG) levels were determined on the plasma from 13 normal subjects. When all samples were measured against a standard curve using no correction factor the range was 45-295 pg/ml (mean ± standard deviation 131 ± 73.8). Using a correction factor the measured fasting glucagon values were 25-60 pg/ml (mean ± S.D. 43 ± 12.3). Fasting glucagon levels as conventionally determined using antiserum 30K are probably inaccurate, and the use of a correction factor is advisable.