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

The research is a analytical comparison of two nonradioactive immunoassay techniques with a conventional radioimmunoassay method for measuring thyroxine levels in horse serum. It revealed that the Homogeneous Enzyme Immunoassay (HEI) method showed higher correlation and precision compared to Chemiluminescent Enzyme Immunoassay (CEI) and hence was identified as a potential substitute for the conventional method.

Research Objective and Methods

• The objective of this research was to compare two nonradioactive testing methods for measuring thyroxine (T4) concentration in horse blood serum, against a conventional radioactive testing method.
• The conventional method used is Radioimmunoassay (RIA), while the two nonradioactive ones are Chemiluminescent Enzyme Immunoassay (CEI) and Homogeneous Enzyme Immunoassay (HEI).
• The researchers collected serum from 85 adult Standardbred horses and analyzed the concentration of T4 in each sample by all three methods.

Comparative Analysis and Findings

• The correlation between the HEI method and the RIA method was significantly higher than the correlation between CEI and RIA.
• The precision of the HEI method was also found to be higher than the CEI method.
• Based on these findings, the HEI method was further evaluated for its between-run precision, linearity upon dilution, and recovery of thyroxine added to equine serum.

Further Evaluation of HEI Method

• The recovery by HEI method of L-thyroxine 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 and when used, improved the average recovery to 94.2% while maintaining excellent linearity.

Conclusions

• The conclusions drawn from the study underline that despite both nonradioactive methods presenting as likely substitutes for the conventional Radioimmunoassay method, the Homogeneous Enzyme Immunoassay method demonstrated the highest correlation and precision.
• The study also suggested that using individually derived in-house correction factors over manufacturer suggested ones can yield more accurate results from the HEI method.