Significance of sex hormone-binding globulin determination

Information for doctors

V.V.Kuzmenko, A.I.Avdeev

Voronezh State Medical Academy named after N.N.Burdenko, Department of Urology. N.N.Burdenko Voronezh State Medical Academy, Department of Urology.

Partial androgen deficiency in men is currently a hot topic of diagnosis and treatment in order to improve the quality of life of patients. Among the causes of decreased androgen levels, an increase in serum levels of sex hormone binding globulin (SHBG) is of great importance. In the blood, it binds the sex hormones: testosterone, 5-dihydrotestosterone, androstenedione, estradiol, and progesterone, limiting the amount of the biologically active (unbound) portion of each hormone.

The concentration of total testosterone in the body is summarised from bound testosterone and biologically active testosterone. Biologically active testosterone accounts for about 43% of the total testosterone content (of which 1 - 3% is free testosterone and 40% testosterone bound to albumin). Most of the testosterone (about 57%) that enters the bloodstream binds to SHBG (sex hormone-binding globulin). SHBG binds both estradiol and estradiol in the plasma, but has a higher affinity for testosterone.

With age, there is an increase in SHPG secretion, which in men can lead, on the one hand, to a decrease in the content of biologically active testosterone while maintaining the content of total testosterone within normal values, and, on the other hand, to an increase in the effects of estrogens. Thirty patients with age-related androgen deficiency were under our observation. The average age of the patients was 55.7+2.8 years. The patients were divided into two groups. In group I patients the examination programme included determination of hormonal status: total testosterone, free testosterone, luteinising hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol, prostatic specific antigen (PSA), TRUS of the prostate and digital rectal examination (DRE). Group II patients additionally included in the complex of examination the determination of SHBG and "free testosterone index" (FTI), calculated as the ratio of total testosterone to SHBG. The results of the examination showed that LH and FSH levels were elevated in all patients, prolactin and estradiol levels were at the upper limit of normal. The level of free testosterone is sharply reduced against the background of relatively normal values of total testosterone in patients of both groups, but the calculation of the free testosterone index showed significant deviations from the norm. PSA, TRUS and PRI data did not reveal any deviations from the norm. Thus, group I patients had only a slight decrease in free testosterone, which, according to laboratory tests, is not an indication for the prescription of corrective therapy. In group II patients, the determination of SHBG showed the presence of pronounced laboratory changes, which corresponded to clinical manifestations and required additional examination and drug correction.

Consequently, the determination of SHBG plays an important role in the diagnosis of age-related androgen deficiency, and the "free testosterone index", or "free androgen index" (FTI, FAI), makes it possible to assess the patient's true androgenic status.