La Testosterone is a male steroid hormone produced naturally in men and, to a lesser extent, in women. It’s a androgenic hormone, whose role is to induce the differentiation and development of male reproductive organs and reproductive function in men. Testosterone is mainly secreted by the testis (95%). In women, androgens come in small quantities from the ovaries and adrenal glands, but especially from the transformation of certain substances (the precursors androstenedione and dehydroepiandrosteone) into testosterone in the liver, adipose tissue and skin.

It circulates in the blood in two forms, one bound to transport proteins (30 to 40% bound to albumin and 60 to 70% bound to SHBG or TeBG and SBP), the other free.

Testing the blood testosterone level is part of the with hormonal in case, for example, ofhirsutism in women or erectile dysfunction in humans or infertility assessment.

Most often, total blood levels are measured, which make it possible to assess the production capacity of the hormone, while the determination of free levels (hormone not bound to transport proteins) makes it possible to estimate tissue availability (1 to 3%). 

In humans

The dosage of plasma testosterone combined with the TeBG assay is the best way to assess the hormonal function of the testis (leydigial function).

The dosage can also be used in men being monitored for prostate cancer and on antiandrogen therapy.

In women

The aim is above all to assess the risk ofhyperandrogenism, that is, excess male hormones, which can cause menstrual disturbances, acne, hirsutism, etc.

In children or adolescents

The dosage can be done in case of puberty disorder, abnormalities of secondary sexual characteristics such as gynecomastia (= breast development) in boys for example.

The blood test is carried out on a venous sample, generally at the bend of the elbow.

It is done in the morning because the concentrations vary throughout the day. Assays should be repeated when an abnormal value is found.

In women, a sample is preferred at the start of the cycle, because the serum testosterone concentration is lowest during the follicular phase of the cycle, and increases to a peak in the middle of the cycle.

It is also possible to measure testosterone in saliva, although this test is less common. The samples are then collected by simple salivation in a flask.

The usual values ​​of testostéronémie are variable according to sex, age and puberty stage.

As a guide, the normal blood testosterone concentrations, which may vary from one laboratory to another, are:

• in humans: 8,2–34,6 nmol / L 
• in women: 0,3–3,0 nmol / L

Only the doctor will be able to interpret the abnormalities according to the symptoms and characteristics of his patient, and if necessary the result of other examinations.

In men, too low testosterone is usually a sign of hypogonadisme (androgen deficiency), either related to a problem with the testis, or of central origin (hypothalamus or pituitary).

Hypotestosteronemia may also be linked to cirrhosis, taking some pharmaceuticals (mitotanes) or a hypothyroidism, among others. Age (andropause) can also be involved.

In women, the main problem with testosterone is hyperandrogenism, defined as excessive secretion of androgens. It manifests itself by several symptoms, especially: hirsutism (coarse hairs on “masculine” areas, such as the chin), acne or seborrhea, menstrual cycle disorders, etc.

It can be linked to several causes, such as:

• polycystic ovary syndrome 
• so-called “virilizing” adrenal or ovarian corticosteroid tumor (testosterone concentration greater than 5,2 nmol / L) 
• ovarian hyperandrogenism 
• adrenal hyperandrogenism