Reassessing free testosterone calculation by liquid chromatography-tandem-mass- spectrometry direct equilibrium dialysis.
J Clin Endocrinol Metab. 2018 Mar 29;:
Authors: Fiers T, Wu F, Moghetti P, Vanderschueren D, Lapauw B, Kaufman JM
Abstract
BACKGROUND: Assessment of free testosterone (FT) might help evaluate androgen status in subjects with borderline total testosterone (T) and/or altered SHBG levels. However, validity of different methods to measure or calculate FT is matter for debate.
METHODS: Serum from 183 women and 146 men was analysed using equilibrium dialysis (ED) with FT directly measured by LC/MS-MS. FT calculation was re-evaluated for the mass action law-based equation according to Vermeulen (cFT-V) , empirical equations according to Ly (cFT-L) and a recently proposed calculation based on a multi-step, dynamic, allosteric model according to Zakharov (cFT-Z).
RESULTS: FT by ED [median13 pmol/L(1.2% of T) in women; 248 pmol/L(1.5% of T) in men] was strongly inversely correlated to SHBG and significantly to albumin in women and only weakly to SHBG in men. Median (p2.5-p97.5) ratio of cFT over ED-FT (EMAS samples) was 1.19 (0.9-1.47),1.00 (0.69-1.42) and 2.05 (1.26-3.26) for cFT-V, cFT-L and cFT-Z. Ratio for cFT-V was not significantly affected by SHBG, T or albumin levels (rank correlations 0.17 to -0.01); ratios for cFT-L and cFT-Z were affected (p<0.05 to p<0.001) and strongly correlated to SHBG (rank correlations 0.72 and 0.75). Rank correlation between cFT% and ED-FT% (for men) are 0.62, 0.74 and 0.89 for cFT-Z, cFT-L and cFT-V.
CONCLUSION: FT results by direct ED confirm prior FT data from indirect ED and ultrafiltration methodologies. Calculations have inherent limitations with clinically important differences among evaluated equations: cFT-V , although overestimating FT, appears the most robust approximation, largely independent of SHBG, albumin and T levels.
PMID: 29618085 [PubMed - as supplied by publisher]
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