Testosterone is the main androgen hormone in men; its synthesis is performed almost exclusively in testicular Leydig cells. Testosterone secretion is controlled by the pituitary luteinizing hormone LH product and is subject to a negative feedback mediated by the hypothalamus and pituitary. Most of the circulating testosterone is bound to sex hormone binding globulin (SHBG = sex hormone binding globulin).
Testosterone is involved both in the development of male sexual characteristics and function in maintaining the prostate and seminal vesicles.
Recommendations for determination of testosterone:
a) Clinical suspicion of androgen deficiency (primary hypogonadism, hypopituitarism, Klinefelter syndrome, Down syndrome, delayed puberty, sexual impotence, infertility, estrogen, cirrhosis);
b) Clinical suspicion of androgen excess: adrenocortical tumors, early puberty.
Limitations and interference
Testosterone concentrations show episodic fluctuations, and circadian cycles. This is why the analysis of a single sample has proven to be clinically relevant only in 68% of cases. So it is recommended to harvest 3 samples in the range of 1 hour to determine testosterone in the sample resulting (link) from the mixture of the three serums.
Total testosterone may be normal in some men with symptoms of androgen deficiency (due to increased levels of SHBG) or in some women with hirsutism. In these cases it is recommended to determine free testosterone.
Almost all severe diseases, especially liver, kidney and circulation can cause decreases in testosterone concentration.
All below substances can lead to higher or lower than normal testosterone levels:
– Valproic acid, barbiturates, bromocriptine, clomifene, estrogen, phenytoin, flutamide, gonadotropin (men), naloxone, rifampicin. (Increase)
– Androgens, carbamazepine, cyclophosphamide, cyproterone, dexamethasone, diazoxide, diethylstilbestrol (1 mg or more), digoxin (in men), ethanol (men alcoholics), phenothiazines, gemfibrozil, glucocorticoids, glucose analogues of GnRH (gonadotropin releasing hormone) in continuous administration, halothane, ketoconazole, magnesium, metoprolol, metirapon, spironolactone, tetracycline, verapamil. (Decrease)
– Oral contraceptives, cimetidine, finasteride, pravastatin, tamoxifen. (Variable effects)
May cause interference with some components of the kit and leads to inconclusive following:
– Treatment with biotin in high doses (> 5 mg / day); it is therefore recommended that blood donation to be made after at least 8 hours after the last administration;
– Very high titers of anti-avidin and anti-ruthenium.