Androgen Replacement Therapy in Women

Marie Lebbe; David Hughes; Nicole Reisch; Wiebke Arlt

Disclosures

Expert Rev Endocrinol Metab. 2012;7(5):515-529. 

In This Article

Measuring Androgen Levels

The production of a sensitive, specific and reproducible assay is challenging, particularly with regards to measuring female testosterone, due to low plasma concentrations and in the concurrent presence of steroids with closely related structures and the possibility of cross-reactivity. As highlighted by the Endocrine Society Guidelines, there is currently an urgent need to define reference ranges for testosterone in female adults.[21] For the previous two decades, radioimmunoassays have been at the forefront of measuring androgen levels and most of our knowledge about the role of steroid hormones in normal women (menstrual cycle, pregnancy, menopause) and endocrine-related disorders is based on studies using radioimmunoassays. The techniques utilizing preassessment organic solvent extraction and chromatography achieve high sensitivity and specificity.[22] However, the direct immunoassays without preceding purification steps, on automated platforms, lack sensitivity and specificity and, importantly, are prone to cross-reactivity problems and should not be used to measure serum levels of testosterone in women.[23] In recent years, mass spectrometry-based assay methods have been increasingly employed for steroid quantification; this approach is exquisitely specific and very sensitive, depending on the specifications of the employed machine, the internal standards used and the sample preparation. These methods are now considered state of the art for steroid hormone measurements. Kushnir et al. published a reproducible preparation technique using liquid chromotography-tandem mass spectrometry and has produced age-related references in children and reference ranges for pre- and post-menopausal women.[24] In women, only approximately 1–3% of testosterone circulates freely (unbound) in the blood, the remainder is bound to sex hormone-binding globulin (SHBG; 65–75%) and albumin (25–35%).[25] The unbound free testosterone is often thought of as being the fraction of the total testosterone that has access to the cell and that results in androgenic effects. However, in reality, the balance between total hormone level and intracellular concentration is more complicated.[26] Bioavailable testosterone is defined as the non-SHGB-bound testosterone and consists of the free and weekly bound albumin fraction.[27] Different methods are available to measure or calculate free testosterone or its surrogate. However, it must be realized that these evaluations depends on the quality of the assay for total testosterone. Testosterone and SHBG levels can be used to calculate the free androgen index: (testosterone nmol/l × 100)/SHBG nmol/l.[1] Equilibrium dialysis for measuring free concentrations of testosterone is desirable as the gold standard, but its use is hampered by its limited availability, high technical requirements and analysis times not compatible with the demands of routine analysis in the high-throughput setting.

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