Serum testosterone measurement in men: evaluation of modern immunoassay technologies

Accurate measurement of serum testosterone (T) is essential for proper diagnosis of androgen deficiency. There are now several modern assay technologies, including automated ones, for measurement of T. In this study, we compared analytical performance of five modern immunoassay technologies commonly used for measurement of total T: Vitros ECi (Ortho-Clinical Diagnostics; normal range (n.r.) 4.6-34 nmol/L); Architect (Abbott Laboratories; n.r. 9.7-34 nmol/L); Access (Beckman Coulter; n.r. 5.3-23 nmol/L); Delfia (Perkin-Elmer; n.r. 9.3-34 nmol/L); and manual EIA DRG kits (n.r. 8.3-42 nmol/L), with the classical RIA (3H-T), after extraction (n.r. 11-33 nmol/L), as a reference method. Total T was measured using all above-mentioned methods in serum samples from 100 male patients, aged 16-65 years. Mean T concentrations in these 100 serum samples assayed by all non-isotopic methods were statistically significantly higher than those obtained by RIA. Delfia showed the highest T levels (19.3 nmol/L versus 12.1 nmol/L by RIA) with a positive bias 60-100%. Almost similar results were obtained using Architect, with a positive bias 40-70%. The closest correlation in results was found between Vitros ECi and RIA (12.7 nmol/L versus 12.1 nmol/L). In the studied samples, the median of differences ranged from minimal (-0.4 nmol/L for Vitros ECi) to maximal (-7.25 nmol/L for Delfia). For all non-isotopic methods, with the exception of Vitros ECi, differences in subjects with low T level (< 10 nmol/L) were statistically significantly larger than in the subjects with high T (T > 10 nmol/L). All other methods showed different degrees of dissimilarities with the RIA, especially in the range of low testosterone concentrations, which is of importance in the clinical assessment of women and pubertal boys.