In men, 90% of blood testosterone comes from the testes and it reflects the function of interstitial cells. Reduced blood testosterone is mostly seen in men with Turner syndrome, mesenchymal cell dysplasia and anencephaly. Causes of lower blood testosterone The physiological properties of testosterone mainly include the following five aspects: 1. Influence embryonic development and promote the growth and development of male accessory organs. Testosterone can stimulate the growth and development of the prostate, penis, scrotum, urethral bulb gland and other accessory sex organs; 2. Stimulate the growth of reproductive organs and the appearance of paraphilias. Testosterone can stimulate and maintain male paraphilias, and can also produce and maintain normal libido; 3. Testosterone is secreted from the interstitial cells and can enter the varicocele through the basement membrane to bind with the corresponding receptors of spermatogenic cells and promote spermatogenesis; 4, affect metabolism. Testosterone can promote protein synthesis, especially protein synthesis in muscles and bones; affect water and salt metabolism, which is conducive to the retention of water and sodium in the body; increase calcium and phosphorus deposition in bone; 5. In addition, testosterone can stimulate the production of erythrocytes and increase the number of erythrocytes in the body. Examination and diagnosis of lower blood testosterone Normal adult male blood testosterone level is 10-35nmol/L (3-10mg/L, RIA method). Decreased testosterone concentration: decreased testosterone levels can be seen in men with hypogonadism, primary testicular hypoplasia infantile, hyperprolactinemia, hypopituitarism, systemic lupus erythematosus, hypothyroidism, osteoporosis, cryptorchidism, and gynecomastia.