[Testosterone deficiency and the problem of normal values].

If a testosterone deficiency is demonstrated, the exact cause of the endocrine hypogonadism should be determined by appropriate endocrinological, imaging and other andrological diagnostic techniques, as such a deficiency can be the result of various illnesses. At present there are no satisfactory evidence based, generally accepted norms for testosterone levels recognised for the aging male. Laboratory analysis of testosterone must be carried out taking into consideration the physiological variability using methods validated in house, with strict internal and external quality control. For the diagnosis of reduced testosterone levels, satisfactorily established own normal values for the technique used are recommended.