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Licensed Unlicensed Requires Authentication Published by De Gruyter June 11, 2014

A simple method for estimating equilibrium constants for serum testosterone binding resulting in an optimal free testosterone index for use in elderly men

H. Alec Ross, Eric J. Meuleman and Fred C. G. J. Sweep


An algorithm was developed to evaluate equilibrium constants for testosterone (Te) and sex hormone-binding globulin (SHBG) or albumin from serum free testosterone (FTe) measurements performed in a panel of 30 healthy elderly men by means of a near-reference method, i.e., symmetric dialysis (affinity constants: SHBG-Te, 1.13×10 9L/mol; albumin-Te, 4.4×10 4L/mol). Using these estimates, a free testosterone index (FTeI) was calculated from total Te and SHBG concentrations in a further 35 elderly men. This FTeI perfectly matches with actually measured free testosterone concentrations by symmetric dialysis in this second group, with a mean ratio index/measurement of 0.998±0.016 (SEM). The efficacy of the algorithm, which represents a simple alternative to previous cumbersome methods for estimation of equilibrium constants, is thereby demonstrated.

Corresponding author: H. Alec Ross, 530 Department of Chemical Endocrinology, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Fax: +31-24-3541484,


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Received: 2004-12-8
Accepted: 2005-3-30
Published Online: 2014-6-11
Published in Print: 2005-6-1

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