Effects of delayed serum separation and long-term storage on the measurement of thyroid hormones in equine blood samples

Studies were conducted to determine the effects of delaying the separation of serum from the clot and of long-term storage of serum samples on the measurement of thyroid hormones in blood from horses using a fluorescence polarization immunoassay. The measured concentrations of T-3 and T-4 were not affected by leaving serum on the clot for as long as 24 hours at room temperatures. Storage of serum for 19 to 22 months at -20 degrees C resulted in significant increases of measured T-4, but not T-3. These studies support previous work demonstrating that thyroid hormones are resistant to degradation, immunologically stable, and reasonably insensitive to potential problems of routine specimen handling when measured with an immunoassay.