Measuring testosterone in women and men.

Measurement of serum testosterone (T) level is of utmost importance for the evaluation of hypogonadism in men and androgen excess in women. Despite the advances in steroid hormone assessment, substantial variability exists regarding measurement of T concentrations. Several factors affect T measurement in men, including circadian rhythms, intra-individual daily variability and transient stressors, while T concentrations in women vary mainly according to the phase of the menstrual cycle. Most of the available immunoassays lack the required accuracy when dealing with T concentrations at the lower end of the normal range for men and across the entire range for females. Consequently, there is no universally accepted lower T threshold for healthy adult men and most immunoassays fail to detect states of mild androgen excess in women. Mass spectrometry is considered the gold-standard method for T measurement; however, due to its complexity and cost, it has not been widely adopted. To increase accuracy, T in men should be measured with a fasting morning sample and repeated if the level is found to be low; in women, measurement must be performed at the follicular phase of the cycle. In both cases, borderline results may be clarified by the assessment of free testosterone (fT). Since most fT assays are unreliable, calculated surrogates should be used instead. Collaborative efforts have been undertaken, with rigorous internal and external quality controls and the establishment of reference methods, to harmonise the commercial assays.