Can serum 17-hydroxyprogesterone and insulin-like factor 3 be used as a marker for evaluation of intratesticular testosterone?

Serum testosterone values vary considerably with little correlation to intratesticular testosterone (ITT). ITT is approximately ~100 times that of serum testosterone and is critical for spermatogenesis. Unfortunately, the only method to accurately measure ITT is invasive testicular aspiration and therefore is not performed routinely. The identification of a serum biomarker for ITT would allow serial monitoring during hormonal manipulation and the ability to assess the effectiveness of a male contraceptive agent. Prior studies have evaluated several serum biomarkers for their ability to accurately reflect ITT with data supporting 17-hydroxyprogesterone (17-OHP) and insulin-like factor 3 (INSL3) as a potential marker. Because evaluation of serum 17-OHP is readily available through commercial laboratories, in this review, we present the evidence for 17-OHP and how it can play a pivotal role in the management of male infertility.