Careful monitoring of temperature is essential when collecting and testing blood or serum samples for measuring testosterone. Otherwise, the hormones will degrade.
Oddoze, C., Lombard, E., & Portugal, H. (2012). Stability study of 81 analytes in human whole blood, in serum and in plasma. Clinical Biochemistry, 45(6), 464-469. https://doi.org/10.1016/j.clinbiochem.2012.01.010