Correlation of two nonradioactive immunoassays to a radioimmunoassay technique for XXXX measurement in equine serum.

@entity1641 @entity1955 @entity2246
The purpose of this study was to compare 2 different nonradioactive assay methods with a conventional radioimmunoassay (RIA) measuring the concentration of serum @entity1955 (T4) in horses. Serum was obtained from 85 adult standardbred @entity1641 . The T4 concentration of each sample was analyzed by RIA, chemiluminescent enzyme immunoassay (CEI), and @entity2246 ( @entity2246 ). The correlation between the @entity2246 method and RIA method was significantly greater (r = 0.89) than the correlation between the CEI and the reference method (r = 0.53). In addition, the precision of the @entity2246 method was significantly greater than the CEI method; within-run percentage coefficients of variation were 4.5% and 15.9%, respectively, at mean T4 concentrations of 19-20 nmol/liter. On the basis of these findings, the @entity2246 method was evaluated further. Both between-run precision and linearity were deemed adequate upon dilution by the @entity2246 method. In addition, recovery of @entity1955 added to equine serum was linear over 6 concentrations tested and averaged 79.6% with a manufacturer recommended data correction factor. An in-house correction factor was calculated by linear regression analysis of the RIA and @entity2246 results from the original equine serum samples. Use of this correction factor improved the average recovery to 94.2% while maintaining excellent linearity (r2 = 0.9978). Although both nonradioactive methods of T4 analysis could likely substitute for the RIA reference method, the @entity2246 method had the highest correlation and precision. The @entity2246 technique also yielded adequately accurate results after correction of the data with an appropriate correction factor. Individually derived in-house correction factors may improve the accuracy of the @entity2246 method to a greater extent than manufacturer suggested correction factors.
