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Bioavailable Testosterone

The measurement of bioavailable serum testosterone is used as a complementary test, as is free testosterone, for the evaluation of hypertrichosis and malnutrition in women as well as for the evaluation of testicular function in clinical situations where serum testosterone blood protein binding, may be affected (obesity, cirrhosis, thyroid disorders).

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Testosterone is the primary male hormone. It is responsible for the development of external genitalia and secondary sexual characteristics in males. In women, its main role is as a precursor to estrogen. In both sexes, it exerts anabolic effects and affects behavior.

In men, testosterone is the main androgen and is secreted by the interstitial cells of the testes, known as Leydig cells. Testosterone promotes the growth and development of the genitals in males, contributes to muscle growth, stimulates hair growth in the armpits, face and pubic area and promotes spermatogenesis. Testosterone is usually measured in tests for the detection of impotence and in the control of infertility.

In women, testosterone is secreted in small amounts by the ovaries and adrenals. Maximum levels are marked in the middle of the cycle. Testosterone measurement is commonly used for the evaluation of ovarian tumors, over-hypertension and for the control of infertility.

The measurement of blood testosterone levels, in combination with the measurement of follicular (FSH) and luteinizing hormone (LH) levels, helps assess the potential dysfunction of the gonads (testes and ovaries) in both sexes. Testosterone circulates in the blood both as free and as plasma-bound proteins (sex hormone-binding globulin, SHBG). Total testosterone is a measure of total circulating testosterone (free and bound). Free or unbound testosterone is the active form of testosterone.

The concentration of free testosterone is very low, usually less than 2% of the total testosterone concentration. In most men and women, about 50% of total circulating testosterone is bound to the sex hormone-binding globulin (SHBG) and the majority is bound to albumin. The usual laboratory methods of analysis used to measure total testosterone are not sensitive enough for the measurement of free testosterone, which makes interpretation of results more difficult.

Usually, the levels of bioavailable (but also free testosterone) are in line with the levels of total testosterone. However, it is known that many conditions and drugs increase or decrease the concentration of sex hormone-binding globulin (SHBG), which may alter the concentration of total testosterone without necessarily affecting the concentration of bioavailable or free testosterone and vice versa.




Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.

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