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.     

Three definitions of metabolic syndrome applied to a sample of young obese men and their relation with plasma testosterone

This study tested 60 men, aged <40 years, with a BMI 27–35 kg/m² to determine whether they had metabolic syndrome. The three definitions used to test this were from the National Cholesterol Education Program (NCEP), the World Health Organization (WHO) and the International Diabetes Federation (IDF). Further, the relationship between a positive definition and plasma testosterone (T) and calculated free T was analysed.

Using the above three definitions of metabolic syndrome (MetS), there was a large degree of overlap of identifying obese men as having the syndrome, but there were quantitatively significant differences as well. So, it is relevant in studies to identify which of the present definitions of the syndrome has been used. With aging there is an increasing prevalence of the syndrome and age itself might be a factor in the lower T levels encountered in these men. But low plasma total T and calculated free T were also consistent features of men <40 years with metabolic syndrome, regardless of which definition had been applied. Including low T levels in the definition of metabolic syndrome, may be helpful.     

Diagnostic significance of free salivary testosterone measurement using a direct luminescence immunoassay in healthy men and in patients with disorders of androgenic status

The accurate measurement of testosterone remains a challenge. The determination of the blood testosterone concentrations in serum by conventional immunoassays is inaccurate in men and even more so in females and children. A new luminescence enzyme immunoassay (LIA) has been developed and validated. The high analytical (8.7 pmol/L) and functional (17.3 pmol/L) sensitivity allows the quantification of the very low concentration in saliva, as well as in serum, after 1/40 dilution. This study measured salivary testosterone levels and compared the results with the free levels calculated from total testosterone and sex hormone-binding globulin in eugonadal and hypogonadal men. Salivary testosterone concentrations in healthy men in morning hours were 369 pmol/L (mean), range 263–544 pmol/L, which was statistically significantly higher than that in men with androgen deficiency, 215 pmol/L (mean), range 51–249 pmol/L.

Repetitive determination of free testosterone concentrations in saliva (once a week for 5 weeks) showed high stability of results over time, with coefficient of variation 9% (range 5–23%).

In this study we showed that free salivary testosterone levels in morning samples correlated well with calculated free testosterone in blood, both in healthy men (R = 0.754, P = 0.001), and in patients with androgen deficiency (R = 0.889, P = 0.0001), though in cases with very low testosterone, salivary concentrations were systematically higher than calculated free testosterone levels in blood.