Endocrine Abstracts

Owing to the difficulties in proper diagnosis of male hypogonadism, there is an ongoing debate on treatment needs of these patients. The comparison of commonly quoted thresholds of serum total testosterone concentrations for considering testosterone replacement therapy surprisingly reveals different thresholds in different European countries. The lower limit of ‘normal’ serum testosterone is 10 nmol/l in Germany, 7.5 nmol/l in France, 7.5–8 nmol/l in the UK, and ~9 nmol/l in Spain. The emerging question is: why are different thresholds of serum testosterone considered as treatment indication for hypogonadism? Is a testosterone laboratory value of 8.5 nmol/l of different relevance for a patient in Germany compared to a patient in France?

For proper laboratory diagnosis of testosterone deficiency some pre-analytical and analytical aspects should be considered. One important pre-analytical aspect is the existence of a significant circadian rhythm of testosterone. I should be noted that the recommended ranges for normal testosterone levels reflect morning levels only. An important analytical aspect is the accuracy and precision of different laboratory assays for testosterone measurement. Depending on the assay system applied values for testosterone levels of exactly the same blood sample may be 7 or 13 nmol/l. The application of different assays might be one explanation for different testosterone thresholds used as indication for treatment of hypogonadal patients by different physicians.

In addition, it has been demonstrated that different thresholds of testosterone concentrations exist for distinctive clinical symptoms of hypogonadism. Hypogonadal patients treated with testosterone show significant inter-individual variation of the association of testosterone levels with clinical symptoms of testosterone deficiency, whereas this association seems to be comparably constant for an individual patient. The decision on the best modality for testosterone treatment should at least in part be based on the accurately measured testosterone level of the individual patient.