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Abstract |
Evaluation of Direct and Indirect Markers to Assess the Androgen Status in Healthy Males during Aging |
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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 mea- sured 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. |
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