[Determination of cortisol, T4, T3 and T-uptake in serum and plasma of horses using fluorescence polarization immunoassays (FIPAs)].

The influence of duration and temperature of storage on hormone levels of whole blood, plasma and serum of horses was investigated. Using FPIAs cortisol, T4 and T-uptake could be measured while the T3-FPIA did not work appropriately. Serum and Plasma stored under the same conditions did not show any difference in cortisol, T4 and T-uptake values. In frozen heparinized plasma samples analysed on different days the cortisol and T4 concentrations fluctuated markedly. The T-uptake values were rather stable. The smallest day by day changes of cortisol and T4 in plasma were found when storing the samples at 20-22 degrees C. At 4 degrees C cortisol decreased markedly while for T4 a clear trend was not found. The cortisol concentration in whole blood stored at 4 degrees C decreased more markedly than in samples stored at 20-22 degrees C. T4 remained stable in whole blood samples stored at 20-22 degrees C over 4 days while showing fluctuations in samples stored at 4 degrees C.