When is bioavailable testosterone a redundant test in the diagnosis of hypogonadism in men?

Objectives: Total testosterone (TT) is frequently prescribed with an SHBG and/or free or bioavailable testosterone measurement. Our objective was to identify a TT range for which subsequent SHBG measurement/calculation adds no additional clinical information. Design and methods: Study data were composed of 3955 sets of TT, SHBG and calculated bioavailable testosterone (cBAT) results from unscreened ambulatory male subjects, aged 18-99. Results: 90% of mismatches between TT and cBAT were observed with TT levels between 6.5 and 13.0 nmol/L, with only slight age variation and no important change with albumin level. SHBG measurement restricted to male patients with TT between 6.5 and 13.0 nmol/L should enable reagent cost savings of over 55%. Conclusion: We suggest that a TT level below 6.5 nmol/L or above 13.0 nmol/L provides sufficient useful information for ruling out hypogonadism in ambulatory adult males. This strategy of BAT testing should lead to significant time and cost savings.