Testosterone is the primary male sex hormone and an anabolic steroid. In male humans, testosterone plays a vital role in developing male reproductive tissues such as the testes and prostate and promoting secondary sexual characteristics such as increased muscle and bone mass and the growth of body hair.

The increased Testo level may be caused by: tumor, hermaphroditism, polycystic ovary syndrome, etc.

The decreased level reflects testis hypoplasia, hypophysis of the anterior lobe, cancer, etc. Combined with serum LH and FSH test results, it can identify primary or secondary testicular dysfunction and precocious puberty in adolescent children.