To what extent are free testosterone (FT) values reproducible between the two Washingtons, and when can calculated FT be used in lieu of direct measurements?

Abstract

Accurate assessment of free testosterone (FT) by equilibrium dialysis and liquid chromatography tandem mass spectroscopy (LCMS/MS) is the gold standard in evaluating many endocrine patients. FT levels can be calculated using measured total testosterone, albumin, and sex hormone binding globulin (SHBG). We hypothesized that a calculated FT value could substitute for measured values. This study compares FT results reported by Walter Reed Army Medical Center (WRAMC) in Washington, DC to results reported by the Seattle Veterans Affairs (VA) Health Care System in Seattle, WA. Calculated FT values are compared to gold standard measurements. Groups 1 and 2 were composed of 54 patients evaluated at the Seattle VA (Group 1) and 94 patients evaluated at a primary care clinic in Alaska (Group 2), whose care resulted in ordering a FT. Group 3 was composed of 64 patients evaluated by the WRAMC endocrine clinic. FT levels were measured by gold standard technology and compared to calculated values. Calculated FT values between the two facilities demonstrated a strong correlation (R2 = 0.98). When comparing calculated FT values to measured levels, Group 3 demonstrated an R2 = 0.93. However, samples from this group with FT values < 50pg/mL demonstrated a poorer correlation (R2 = 0.45). Calculated FT values may be substituted in the clinical setting for gold standard technology when levels are > 50pg/mL.