Endocrine Abstracts

Objective: Biochemical assessment of male hypogonadism relies on estimation of freely available testosterone. Gold standard measurement is by equilibrium dialysis but this is not practical in clinical use. We compared two calculation methods; bioavailable (non-SHBG bound) testosterone (Morris et al.), and free (non-SHBG non-albumin bound) testosterone (Vermeulen et al.) for their diagnostic performance.

Design: Free testosterone and bioavailable testosterone were assessed for agreement for a cohort of 301 males with symptoms of hypogonadism.

Methods: Total testosterone was measured by chemiluminescence competitive binding assay by Siemens. Sex hormone binding globulin (SHBG) was measured by chemiluminescence double antibody assay by Siemens. Free testosterone was calculated by the method of Vermeulen et al., and bioavailable testosterone by the method of Morris et al. Regression analysis was used to compare the two.

Results: We found that the Vermeulen free T=0.174 nmol/l corresponds to Morris bioavailable of 2.7 nmol/l. The correlation between the two methods is good (R²=0.92).

Conclusions: For patients with symptoms of hypogonadism in our area there is no significant difference in diagnostic performance between bioavailable and free testosterone as calculated by the above methods.