Canine immunoreactive insulin quantitation using, five commercial radioimmunoassay kits

Five commercial radioimmunoassay (RIA) kits developed for quantitation of human immunoreactive insulin (IRI) were evaluated for their capability to quantitate canine IRI. Evaluation criteria included precision, dilutional parallelism, sensitivity, and comparison of IRI concentration in 4 control sera. One RIA kit had good dilutional parallelism, consistently good precision, and adequate sensitivity. Other RIA kits had poorer performance in dilutional parallelism or precision. No RIA kit quantitated the same IRI concentrations in all 4 control sera as did another. The results indicated that quantitation of canine IRI by some commercial RIA kits (for human use) may not be reliable. Variations in IRI concentrations quantitated indicated that reference intervals for healthy dogs should be established for each insulin RIA. At least 17 commercial radioimmunoassay (RIA) kits are available to quantitate human immunoreactive insulin (IRI). Two RIA kits have been used to quantitate canine IRI, but validation of assays to quantitate canine IRI were not reported. Evaluation of RIA validity should include assessment of specificity, precision, sensitivity, and accuracy. Two methods are recommended for assessing specificity: (i) demonstration of dilutional parallelism, and (ii) demonstration that related substances do not influence quantitation of analyte. Human insulin differs from canine insulin by having 1 amino acid substitution at the carboxyl-terminal of the B chain. Thus, it is possible that antibodies developed to react with human IRI will have cross immunoreactivity with canine IRI. Precision is affected by a variety of factors including technical steps and antigen-antibody interactions.(ABSTRACT TRUNCATED AT 250 WORDS)