Cross reactions in radioimmunoassay: a mathematical model for correcting assay results, as exemplified by eliminating the interference of intact thyrotropin in an assay of its beta subunit.

摘要

To correct the results of a radioimmunoassay for beta-thyrotropin (TSH) subunit by eliminating the proportion ascribable to intact TSH, we have devised a method that experimentally reproduces the conditions under which the interference develops. Beta-TSH subunit was assayed in several preparations containing known concentrations of both beta-TSH and TSH. The TSH-induced overestimation of beta-TSH was linearly related to the concentration of antigen in the sample. At a constant concentration of TSH, therefore, the following equation is applicable: F = aE + b, where F is the measured (but overestimated) concentration of beta-TSH, E is the actual concentration of beta-TSH, and a and b are the slope and the intercept of the regression line, respectively. a and b, once expressed as a function of TSH, allow the correction of the overestimation. The analysis of the results according to the mass action and conservation laws shows that the antiserum is more avid for the interferent (intact TSH) than for the antigen (beta-TSH).