What to Measure: Testosterone or Free Testosterone?

Abstract

Accurate and precise measurement of serum testosterone is adequate for the diagnosis and monitoring of testosterone replacement for most men with testosterone deficiency. Serum testosterone measurement should be obtained in the morning, preferably in fasting state, and a repeat sample for confirmation is advisable. The sample should be sent to a reliable laboratory that practices accuracy-based proficiency tests or external quality control programs and quotes a reference range of serum testosterone levels of adult men between 250 and 1000 ng/dL (8.7–34.7 nmol/L). The use of free testosterone measurements as a primary diagnostic tool for male hypogonadism has remained controversial. Free testosterone measurements may provide additional information if there are issues with the concentration or the binding of testosterone to sex hormone binding globulin (SHBG). Free testosterone should be measured by equilibrium dialysis which is available in reference laboratories or by calculated free testosterone using formulae that had been validated based on accurate and precise measurements of both testosterone and SHBG. The most common clinical use of free testosterone is for the diagnosis of older men with testosterone deficiency who may be overweight.