Which is the best test for the diagnosis of testosterone deficiency – total or free testosterone?


In many situations in clinical practice, free testosterone must be determined because SHBG levels can vary across a wide range. There are several assays for both total testosterone and free testosterone, each with its own pros and cons. It is recommended that free testosterone is determined by calculation.

Conditions that decrease SHBG levels – and by implication increase free testosterone levels – include obesity, type 2 diabetes, glucocorticoids and nephrotic syndrome. Conditions that decrease free testosterone levels - and by implication decrease free testosterone levels - include older age, estrogen, thyroid hormones and HIV.

In large epidemiological studies the correlation between total testosterone and free testosterone is good. However, in clinical practice individual patients often have widely varying SHBG levels. Determination of free testosterone levels is a prerequisite for treating and monitoring patients on an individual basis.



Prof. Dr. med. Marija Pfeifer

Adrian Dobs, MD
Professor of Medicine and Oncology
Division of Endocrinology, Diabetes and Metabolism
John Hopkins University, School of Medicine


  • Groti K, Zuran I, Antonic B, Forsnaric L, Pfeifer M. The impact of testosterone replacement therapy on glycemic control, vascular function, and components of the metabolic syndrome in obese hypogonadal men with type 2 diabetes. The aging male : the official journal of the International Society for the Study of the Aging Male. 2018;21(3):158-169. Return to content