Use of calculated free testosterone in men: advantages and limitations.

Abstract

Purpose of review: Due to technical requirements and high cost, equilibrium dialysis-free testosterone (T) measurements are not commonly available in clinical practice. Clinicians rely on calculated free T (cFT) as a proxy. This review discusses using free T as a second-line assessment, highlighting its relevance in preventing misdiagnosis and overtreatment of male hypogonadism.

Recent findings: While there is consensus on measuring total T - comprising sex hormone-binding globulin (SHBG)-bound, albumin-bound, and free T - as a first step in diagnosing male hypogonadism, evidence confirms that aging and conditions like obesity influence both total T and SHBG levels. Furthermore, low free T has been associated with symptoms of androgen deficiency, even in men with normal total T. Clinicians should, however, be aware of limitations of free T calculations, particularly the lack of standardization. Recent developments include establishing age-stratified free T reference ranges measured by equilibrium dialysis.

Summary: Free T remains a subject of longstanding controversy. Factors such as age and obesity can alter total T and SHBG levels. Free T serves as a second-line indicator of androgen exposure, taking SHBG fluctuations into account. Given that commonly used free T calculators only provide approximations of free T, there is a need to further standardize free T calculators.