Serum testosterone bioassay evaluation in a large male cohort

Summary Objective To assess if a cell-based readout of androgen action in serum demonstrates a closer association with recognized classical parameters of androgen action in men than current measures of serum testosterone (T). Design To develop, validate and utilize a mammalian cell-based assay to measure specifically bioactive T and determine if this measure is a physiologically relevant fraction of serum T. Measurements and participants We have developed a specific serum T bioassay using human prostate cancer cells. A rapid 5-min exposure to 100% serum followed by serum withdrawal confers specificity of the assay to serum T and provides sufficient sensitivity to measure T in male serum samples. Matrix effects were experimentally discounted as a confounding issue. A total of 960 male serum samples from the Florey Adelaide Male Ageing Study (FAMAS) with previous comprehensive cohort data and serum measurements were utilized. Results Bioassay T measurement in the 960 FAMAS serum samples returned a median of 10AE7 nmol/l (1AE7–45AE4), and was most closely related to immunoassayed total T, but not immunoassayed bioavailable T or calculated free T. Immunoassayed total T demonstrated a positive association with isometric grip-strength (R 2 =0 AE127, P