Normal testosterone (TTT) in an assay at the BC Cancer laboratory is now defined as >3.5ug/ml. It combines free TTT (left) with albumin bound TTT (top right) and sex hormone binding globulin bound TTT (bottom right). These make up approximately 1-2%, 35% and 65% of TTT respectively. The first two combined make up the bioavailable TTT. This is the important component in a ‘true’ diagnosis of hypogonadism, but is not measured by many laboratories. It is therefore possible for a man to have a ‘low normal’ TTT at BC Cancer and have hypogonadism defined by the bio TTT. Testosterone levels decline with age.
Increasing incidence of hypogonadism with age by various assays. Harman et al. J Clin endocrinal Metab 2001; 86(2): 724-31.
