Methodology for measuring testosterone, dihydrotestosterone and sex hormonebinding globulin in a clinical setting

Testosterone is a hormone difficult to measure accurately. Yet, its accurate determination is the prerequisite for the correct diagnosis and clinical management of hypogonadism in males and hyperandrogenism in females. In the last decade a number of studies increased awareness of the poor performance of most of the current assays and identified some strategies to improve the accuracy of testosterone testing (Rosner et al. 2007; 2010). In the previous edition of this book a chapter was dedicated to the description of the principles, analytical performance and limitations of the existing methodologies for measuring testosterone, DHT and SHBG (Simoni 2004). Here, we will provide an update on the state of the art to help the reader choose the testosterone detection system most suitable for his/her needs in view of the current recommendations. Testosterone and DHT circulate in serum largely bound to transport proteins: that is albumin, which displays low affinity but very high binding capacity, and SHBG, with high affinity and low capacity. A systematic analysis of serum transport of steroid hormones and their interaction with binding proteins revealed an association constant of SHBG of 1.6 × 109 M-1 for testosterone and of 5.5 × 109 M-1 for DHT at 37 C (Dunn et al. 1981). By comparison the association constant of albumin for testosterone is five orders of magnitude lower (6 × 104 M-1) (Anderson 1974). The relative amounts of protein binding of circulating testosterone in men and women are shown in Table 4.1.