When the sperm density of infertile patients is zero or very low, the total testicular volume is small and soft, and the measured FSH is more than 2 times above the normal range, it can already indicate serious damage to testicular spermatogenesis, and there is no need to perform testicular biopsy to confirm the diagnosis. If the sperm density of infertile patients is zero, the testicular volume is normal, and the FSH is also within the normal range with positive seminal plasma fructose, the majority of these patients have obstructive azoospermia. In any case of azoospermia with differences between testicular size and FSH levels, testicular biopsy is considered to clarify testicular spermatogenesis.