Storage conditions and stability of thyrotropin and thyroid hormones on filter paper

We evaluated the effects of temperature and humidity on thyroid hormones (T4, T3) and thyrotropin (TSH) measured in blood spots dried on filter paper. RIAs for T4 and T3 blood spots were optimized to measure these analytes over the neonatal and euthyroid adult reference intervals. Sensitivities of the T3 and T4 assays were 0.5 and 10 nmol/L, respectively. A blood-spot immunoradiometric assay for TSH involving magnetizable particles was developed with a sensitivity of 6 milli-int. units/L. Control sera stored at -20 degrees C, 4 degrees C, room temperature, 37 degrees C, and at external ambient temperatures for 36 days showed no significant change in measured concentrations of TSH or T3 during 30 days or for T4 at -20 and 4 degrees C. T4 markedly declined in blood spots stored at room temperature (either high or low humidity), 37 degrees C, or ambient temperature. TSH and T3 in blood spots evidently are stable at temperatures likely to be encountered during storage or transport, but blood spots for T4 assay must be stored between -20 and 4 degrees C.