In men, 90% of blood testosterone comes from the testes, and it reflects the function of the mesenchymal cells. Decreased blood testosterone is often seen in men with Turner syndrome, mesenchymal stromal cell hypoplasia, and anorchidism. How to differential diagnosis of lowered blood testosterone? 1, XX male syndrome: the sex chromosome of this syndrome is XX, without Y chromosome, H-Y antigen can be measured in serum, suggesting that there is a small amount of Y embedded in X or autosomes, which can’t be detected in in vitro culture. The phenotype is male, with an incidence of 1:20,000-24,000 in male infants.The patient lacks all female internal genitalia and has male psychosexual characteristics. The clinical picture is similar to that of Klinefelter’s syndrome: the testes are small and hard (usually less than 2 cm), there is often gynecomastia, the penis is normal size or slightly smaller than in a normal adult, and there is usually a lack of spermatozoa and vitreous degeneration of the varicocele. Blood testosterone levels are decreased, estradiol levels are increased, and gonadotropin levels are elevated. Clinically this type resembles XXY/XY chimerism. Short stature, mental retardation and personality changes are mild and rare, and the incidence of hypospadias is increased. 2, male Turner syndrome: autosomal dominant inheritance, karyotype 46, XY, with typical clinical manifestations of Turner syndrome: short stature, neck webbing, elbow ectropion, congenital heart disease, male phenotype. There is often cryptorchidism, testicular shrinkage, varicocele hypoplasia, sexual naivety, decreased blood testosterone and increased serum gonadotropin levels. A few patients have normal testes and are fertile. 3.Mesenchymal cell hypoplasia: fetal mesenchymal cell secretion of testosterone is impaired, resulting in male pseudohermaphroditism. There are testes but spermatogenesis is impaired. Vulvar malformation, a female phenotype, with a penis resembling a clitoris and a blind-ended vagina, but without a uterus or fallopian tubes, and primary amenorrhea is found only at puberty. Pubic and axillary hair was sparse. Patients have elevated FSH and LH basal values, significant gonadotropin response to GnRH test, markedly low blood testosterone, and no increase in HCG stimulation. 4.Aorchidism: embryonic period due to infection, trauma, vascular embolism or testicular torsion causes complete atrophy of the testis and causes the disease, the phenotype is male. The male secondary sexual characteristics do not develop at puberty, and the external genitalia still remain childish type with no testicles, and if androgen treatment is not given early, eunuch body type will appear. If there are residual or ectopic mesenchymal cells secreting androgens, modest secondary sexual characteristics may develop. Blood testosterone levels are low, gonadotropins are significantly elevated, and testosterone does not increase after HCG stimulation. 5.Hypoplasia of adult human mesenchymal cells: also known as male menopause syndrome. After the age of 50, men gradually experience hypogonadism, which may be characterized by personality and mood changes. Blood testosterone gradually decreases, gonadotropin increases, and sperm decreases or lacks.