Accessible 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

Abstract

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,

References

1 Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 1999; 84: 3666–72. Search in Google Scholar

2 Dunn JF, Nisula BC, Rodbard D. Transport of steroid hormones: binding of 21 endogenous steroids to both testosterone-binding globulin and corticosteroid-binding globulin in human plasma. J Clin Endocrinol Metab 1981; 53: 58–68. Search in Google Scholar

3 Moll GW, Rosenfield RL, Helke JH. Estradiol-testosterone binding interactions and free plasma estradiol under physiological conditions. J Clin Endocrinol Metab 1981; 52: 868–74. Search in Google Scholar

4 Vermeulen A, Stoica T, Verdonck L. The apparent free testosterone concentration, an index of androgenicity. J Clin Endocrinol Metab 1971; 33: 759–67. Search in Google Scholar

5 Swinkels LM, van Hoof HJ, Ross HA, Smals AG, Benraad TJ. Concentration of salivary testosterone and plasma total, non-sex-hormone-binding-globulin-bound, and free testosterone in normal and hirsute women during administration of dexamethasone/synthetic corticotropin. Clin Chem 1991; 37: 180–5. Search in Google Scholar

6 Van Uytfanghe K, Stöckl D, Kaufman JM, Fiers T, Ross HA, De Leenheer AM, et al. Evaluation of a candidate reference measurement procedure for serum free testosterone based on ultrafiltration and isotope dilution-gas chromatography-mass spectrometry. Clin Chem 2004; 50: 2101–10. Search in Google Scholar

7 Bevington PR. Data reduction and error analysis for the physical sciences. New York: McGraw-Hill, 1969:56–66. Search in Google Scholar

8 Swinkels LM, van Hoof HJ, Smals AG, Ross HA, Benraad TJ. Interdependence of non-sex-hormone-binding globulin-bound testosterone and cortisol. Clin Chem 1991; 37: 1461. Search in Google Scholar

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

© Walter de Gruyter Berlin New York