Calculated Free Testosterone Accuracy Based on SHBG Levels

SHBG Threshold for cFT Accuracy

Calculated free testosterone (cFT) calculations are reliable for most clinical evaluations but have specific limitations based on SHBG levels, particularly when SHBG concentrations fall below 30 nmol/L, at which point direct measurement by equilibrium dialysis is recommended for better accuracy 1
The accuracy of cFT decreases significantly when SHBG concentrations fall below 30 nmol/L, and the Free Androgen Index (FAI) also becomes inaccurate in such cases 1

Mass spectrometry methods (LC-MS/MS) for measuring total testosterone provide superior sensitivity and specificity compared to direct immunoassays when calculating cFT 1
cFT calculated from high-quality total testosterone and SHBG measurements has shown high diagnostic accuracy with a pooled sensitivity of 0.89 and specificity of 0.83 2, 1

When using cFT calculations, prioritize total testosterone measurements by LC-MS/MS over immunoassay methods for improved accuracy 2, 1
Equilibrium dialysis is considered the gold standard for free testosterone measurement, providing better accuracy, especially when SHBG levels are ≤30 nmol/L, and albumin levels are ≤3.5 g/dL 1