Are There Variances Of Calculated Free Testosterone Attributed To Variations In Albumin And Sex Hormone-Binding Globulin Concentrations In Men?

Abstract

Calculated free testosterone (cFT) is determined from total testosterone (TT), sex hormone binding globulin (SHBG), and albumin (Alb) levels using mathematical formulae. Variations in cFT due to changes in SHBG or Alb have not been investigated. We evaluated potential cFT variances determined with fixed Alb (4.3 g/dL) and measured Alb, and the point at which low SHBG and Alb combinations produced significant cFT variance. We analyzed 11,176 data points from 5,797 men. cFT values with fixed versus actual Alb values were evaluated and compared. cFT levels were theoretically determined for all possible combinations of TT, SHBG, and Alb (8,343,552 combinations). Agreement between the 2 measures was assessed with Lin's concordance coefficient. Mean Alb was 4.06 ± 0.32 g/dL. Mean SHBG was 39.0 ± 23.6 nmol/L. A fixed Alb of 4.3 g/dL did not produce significant variance for most cFT evaluations. Accuracy decreased when Alb was ≤3.5 g/dL in combination with SHBG ≤30 nmol/L, and this occurred in 1.2% of all data points. A fixed Alb of 4.3 g/dL is acceptable for most clinical evaluations. If Alb is ≤3.5 g/dL and SHBG is ≤30 nmol/L, the variance increases, and a free testosterone (FT) measurement by equilibrium dialysis is warranted for better accuracy.