Testosterone, free calculated

Testosterone (S-Testo) is a male sex hormone or androgen that is found in both men and women. Testosterone production is controlled by luteinising hormone (S-LH) secreted by the anterior lobe of the pituitary gland. Men produce testosterone in the testes and women in the ovaries but both sexes also produce testosterone in the adrenal gland.

Testosterone affects the growth of the sex glands and external genital organs, body hair, muscle and bone development and deepening of the voice. In addition to physical effects, testosterone affects social and sexual behaviour. Boys start to produce testosterone in the testes during puberty, and development continues throughout life. Production declines in older age, however.

The majority of testosterone is transported in blood, bound to sex hormone binding globulin (SHBG). Only a small amount of testosterone, approximately 1–3% in men and 0.5–1.3% in women, is free in the blood. Because production of testosterone in the tests varies by the time of the day, blood testosterone levels are highest and should be measured in the morning. For women, testosterone would be best to measure on 5.-8. day of the cycle.

When is a good time to measure free calculated testosterone levels?

Testosterone levels in males are measured when it is suspected that not enough testosterone is secreted (hypogonadism). It is also measured when examining the cause of infertility, lack of sexual desire and impotence.

In women, testosterone levels are measured when examining the cause of infertility or ovarian dysfunction or when a tumour that produces too much testosterone is suspected.

Symptoms indicating disturbances in the level of testosterone include:

• Infertility
• Loss of libido
• Erectile dysfunction
• Irregular menstrual periods or amenorrhea (absence of menstruation)
• In women, excessive growth of hair, low voice or balding
• Balding
• In boys, delayed or slow puberty
• In boys, abnormally early onset of puberty (precocious puberty)
• Fatigue
• Impaired concentration
• Sleep disorder
• Obesity

What does the test measure?

A blood testosterone test is used to measure the total amount of testosterone in blood. If the concentration of testosterone transport proteins in blood changes, the total testosterone concentration changes as well. In situations where it's justifiable to suppose that the concentration of plasma's proteins has changed, the amount of free testosterone should be measured.