Evaluation of direct and indirect markers to assess the androgen status in healthy males during aging.

Evaluation of the male androgen status requires a marker that reflects the biologically active fraction of plasma testosterone. The serum sex hormone-binding globulin (SHBG) concentration is not suitable here because of its wide inter-individual scatter. As potential biological markers of the active testosterone fraction we compared indirect methods calculated on the basis of SHBG and total testosterone measured by fully automated IMMULITE 2000 assays (DPC, Los Angeles, CA, USA), and total testosterone alone with direct free testosterone measured by RIA (DPC). Indirect methods were the free androgen index FAI, calculated free testosterone cFT, and calculated bio-available testosterone cBT. Further androgens measured were DHEAS and androstenedione. Blood samples were collected from a cohort of 446 healthy men aged between 20-99 years. All parameters except SHBG decreased significantly during aging. The direct free testosterone assay was significantly correlated with the indirect androgen parameters. This is in accordance with earlier results using LC-MS as the gold standard method. The strongest correlation was seen with cBT/measured albumin (r=0.750), though the direct testosterone RIA does not measure the entire unbound fraction of testosterone, and total testosterone can rapidly be measured with an automated assay system. It was found that a fixed albumin concentration of 43 g/L is a reasonable calculation basis for cBT in subjects of <70 years. In the elderly >70 years or persons with known pathologies of the androgen axis, it is commendable to measure the albumin concentration individually. In conclusion, calculated bio-available testosterone (cBT) is the best marker to reflect the bioactive testosterone fraction, i.e. the androgen status in males.

Reference intervals for testosterone, androstenedione and SHBG levels in healthy females and males from birth until old age.

The measurement of androgen levels is important in the follow-up of sexual development and in the diagnosis of disturbances of the gonadal function in children and adults. The aim of this study was to evaluate the age dependence of the serum concentrations of testosterone, androstenedione, and SHBG from birth until old age using the IMMULITE 2000 automated assay system (DPC, Los Angeles). Testosterone and androstenedione median levels were very high during the first weeks of life due to residual maternal hCG and decreased to low basal levels around the detection limit of the assay. With the onset of puberty around the age of 10 years both parameters increased strongly, reaching a maximum at about 17 years (testosterone: > 20-fold in boys, 2-fold in girls; androstenedione: 10-fold in boys, 5-fold in girls). In both girls and boys, we measured a decline in the SHBG medians during sexual maturation. This decline was more pronounced in boys (median 78.3 to 26.2 nmol/l from Tanner stage 1 to 5) since the higher androgen levels are thought to down-regulate SHBG. In male adults a continuous decrease was seen for testosterone from a median of 16.1 nmol/l in age group 21-30 years to 9.7 nmol/l in the age group > 70 years. In women the testosterone levels which were only about 5% of that of men from the same age group decreased only slightly, starting from a median of 0.9 to 0.6 nmol/l. In both sexes androstenedione levels decreased continuously during aging. In contrast to the androgen levels, the median SHBG levels increased steadily in men from 20.8 to 44.5 nmol/l, while the median SHBG levels in women decreased from 78.3 to 44.5 nmol/l in the age group of 61-70 years. Interestingly, the SHBG levels rose again in women of the group > 70 years. The reference intervals elaborated here may help in the assessment of the status of sexual development, and to diagnose pathologies of the gonadal axis or hypogonadism during aging.