[Laboratory work-up of testosterone].

Measuring testosterone concentration is a central component of routine andrological diagnostics. To avoid complicated and often imprecise direct measurement of bioavailable testosterone, calculation by SHBG and albumin concentration is possible. When interpreting a measured testosterone concentration, numerous influencing factors have to be kept in mind. One main factor is circadian rhythm; furthermore, concentration decreases with advancing age. Changes of testosterone concentration can be caused by illness or the intake of specific drugs. The increase in SHBG concentration with age is of particular importance. Since internationally accepted standard values are missing, especially for elderly patients, their symptoms should always be considered when making a decision on hormone substitution.