[Testosterone-binding capacity, free-plasma testosterone fraction, and free-plasma testosterone concentration in...

Testosterone-binding capacity (TeBG), free-plasma testosterone fraction (%FT), and free-plasma testosterone concentration (AFT) were measured in 24 men with primary and 14 with secondary hypogonadism of various causes, as well as in eight with coital impotence. There was a highly significant correlation between TeBG and %FT (r = minus 0.891; P less than 0.0005). TeBG and %FT did not generally differ from normal in primary hypogonadism, while AFT was normal or decreased, depending on the corresponding whole testosterone concentrations. In secondary hypogonadism there was always an increased TeBG and decreased %FT. Depending on whole testosterone concentration, AFT was low or very low. In impotent subjects TeBG, %FT and AFT were generally normal. The role of AFT determination in andrological diagnosis is discussed.