The value of %free testosterone (%FT) is determined by the amount of testosterone that circulates free and unbound compared to total testosterone. Total testosterone includes that bound to sex hormone binding globulin (SHBG) and albumin as well as free T. The %free testosterone will increase as SHBG decreases and low SHBG may increase risk of prostate cancer.
Standard Range: Male 1 - 2.9%
The ODX Range: Male 1.6 - 2.9%
Low %free testosterone may indicate a lower level of circulating unbound active testosterone relative to total testosterone and an increasing SHBG (Albisinni 2012),
High %free testosterone may be associated with low SHBG (Albisinni 2012), overproduction of endogenous testosterone, or supplemental testosterone.
While most testosterone circulates bound to plasma proteins, primarily SHBG, approximately 1-3% circulates in the active unbound or free form (Krakowsky 2015, Antonio 2018).
The %FT is influenced by total testosterone, SHBG, albumin levels, and age, as well as by obesity, alcohol consumption, and genetic variations that determine SHBG levels. Research suggests that %FT is associated with risk of high-grade prostate cancer, although the relationship between androgens and prostate cancer is considered complex. A prospective single-center study of 812 Italian men undergoing prostate biopsy found that %FT was significantly higher in those with high-grade prostate cancer compared to low-intermediate grade. Researchers suggest the association is related to lower total testosterone as well as lower SHBG which is thought to increase risk of prostate cancer in general. The %FT increases as SHBG decreases (Albisinni 2012).
Albisinni, Simone et al. “Greater percent-free testosterone is associated with high-grade prostate cancer in men undergoing prostate biopsy.” Urology vol. 80,1 (2012): 162-7. doi:10.1016/j.urology.2012.01.068
Antonio, L et al. “Free Testosterone Reflects Metabolic as well as Ovarian Disturbances in Subfertile Oligomenorrheic Women.” International journal of endocrinology vol. 2018 7956951. 10 Sep. 2018, doi:10.1155/2018/7956951
Krakowsky, Yonah, and Ethan D Grober. “Testosterone Deficiency - Establishing A Biochemical Diagnosis.” EJIFCC vol. 26,2 105-13. 10 Mar. 2015