Effects of storage, hemolysis, and freezing and thawing on concentrations of thyroxine, cortisol, and insulin in blood samples.

Blood samples were collected from six Beagle dogs to determine effects of precentrifugation and postcentrifugation storage times and temperatures, hemolysis, and repeated freezing and thawing on concentrations of thyroxine (T4), cortisol, and insulin as determined by radioimmunoassay. Concentrations of T4 did not change in whole and clotted blood stored for 72 hr at 4" or room temperature (22-26") and in serum stored for 8 days at -20", 4", or room temperature. Mean cortisol concentrations decreased (P < 0.01) in clotted and heparinized blood stored for 72 hr at room temperature. Mean insulin concentrations decreased (P < 0.01) in clotted blood stored for 24 hr and in EDTA-treated and heparinized whole blood stored for 72 hr at room temperature. After centrifugation, mean cortisol concentrations in serum decreased 21% (P < 0.01) by 2 days and 57% (P < 0.01) by 8 days at room temperature. Insulin decreased 20% (P < 0.05) by 2 days and 72% (P < 0.01) by 8 days at room temperature. Degradation of both hormones was prevented by storing at 4" and -20". Hemolysis accelerated disappearance of insulin immunoactivity at 4" as well as room temperature (P < 0.01). Repeated freezing and thawing of serum did not affect concentra- tions of any hormones studied. Our results clearly show that factors such as storage time, storage temperature, and hemolysis changed concentrations of hormones sufficiently to alter interpretation of research and clinical data.