Evaluating Calculated Free Testosterone as a Predictor of Morbidity and Mortality Independent of Testosterone for Cross-sectional and 5-Year Longitudinal Health Outcomes in Older Men: The Concord Health and Ageing in Men Project
To determine whether calculated free testosterone (cFT) provides prognostic information independent of serum T for predicting morbidity and mortality in older men in cross-sectional and 5-year longitudinal analyses. We studied men aged ≥70 years at baseline (n = 1,705), 2-year and 5-year measuring serum T (liquid chromatography-mass spectrometry), SHBG (immunoassay), cFT (an assumption-free empirical formula) together with 24 morbidity and 4 mortality outcomes. For cross-sectional and longitudinal analyses we employed a joint prediction model using generalized estimating equation models adjusted for age, smoking, comorbidities, and body mass index (BMI) with men having both normal T and normal cFT as referent group. Most morbidity and mortality outcomes were predicted by a combination of low T and cFT (LL). By contrast, only a single morbidity outcome in cross-sectional and none in longitudinal analysis was predicted by low T/normal cFT (LN) or normal T/low cFT (NL) without significant LL associations (isolated discordance). While for the few outcomes that predicted morbidity in men with discordances (LN or NL), these predictions only occurred when LL was also significant. Hence, for morbidity or mortality prediction in older men, discordance between cFT and T is unusual and isolated discordance is rare, so that cFT provides minimal independent prognostic information over serum T.