Accuracy of calculated free testosterone differs between equations and depends on gender and SHBG concentration

Jennifer S. Hackbarth, Jonathan B. Hoyne, Stefan K. Grebe, Ravinder J. Singh

Research output: Contribution to journalArticle

38 Scopus citations

Abstract

Serum free testosterone (fT) concentrations are often calculated, however different equations often yield discrepant results. This study explores the sources of this variability. We compared three established and two new equations that differed only by their testosterone association constants with isotope dilution equilibrium dialysis in two patient groups with different gender distributions. Equation components were examined to determine how they impacted correlation with isotope dilution equilibrium dialysis. Association constants derived for each patient group correlated best with isotope dilution equilibrium dialysis for that group and not the other set. Samples with the poorest correlation between isotope dilution equilibrium dialysis and calculated fT results had significantly higher SHBG concentrations. Regardless of equation, ≥25% of samples showed unacceptable deviation from isotope dilution equilibrium dialysis. Association constants and gender makeup and SHBG concentration of the patient groups used to establish an equation all significantly impact correlation with isotope dilution equilibrium dialysis. Application of many fT equations to wider populations will therefore frequently yield results that differ substantially from isotope dilution equilibrium dialysis.

Original languageEnglish (US)
Pages (from-to)48-55
Number of pages8
JournalSteroids
Volume76
Issue number1-2
DOIs
StatePublished - Jan 1 2011

Keywords

  • Free testosterone
  • Free testosterone calculation
  • Isotope dilution equilibrium dialysis
  • Mass action equation
  • Sex hormone binding globulin
  • Testosterone

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology
  • Pharmacology
  • Clinical Biochemistry
  • Organic Chemistry

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