Effect of time, temperature and freezing on the stability of immunoreactive LH, FSH, TSH, growth hormone, prolactin and insulin in plasma.

1. Endogenous LH, FSH, TSH, growth hormone, prolactin and insulin were measured by radioimmunoassay in human plasma samples stored at 4 degrees, 20 degrees and 37 degrees for up to 8 days or repeatedly frozen and thawed. 2. At 4 degrees, the concentrations of all hormones were stable for at least 8 days; at 20 degrees only LH, FSH and TSH were stable for 8 days; at 37 degrees only TSH was stable for 8 days. 3. All the hormones except insulin were stable during 5 freeze-thaw cycles.