There are several factors that can affect a patient's seminal quality. These factors can be divided into four groups: anatomical, hormonal, infectious, and genetic.
In the case of anatomical factors, they can be divided into congenital (from birth) and acquired. Congenital factors may be due, for example, to inadequate formation of the testes or to the testes remaining in the abdominal cavity and not in the scrotal sac. Acquired factors may be due to testicular trauma, tumors or alterations in the circulation of the testicles that cause their sperm production to be inadequate (varicocele).
As for the hormonal factors, it must be explained that the production and maturation of sperm depend on a hormonal cycle that involves different hormones; an imbalance of these hormones can affect seminal quality. To find out if this is the patient's case, it will be enough to do a blood test and assess his hormone levels.
On the other hand, there are infections that can alter seminal quality. These can be viral infections in childhood, which can alter male fertility in adulthood, or infections in adulthood, which affect the testicle or the pathways through which sperm are transported to the testicle.
Finally, there are genetic factors that can cause males to have diminished sperm quality or simply not be able to produce spermatozoa. These are the case of genetic syndromes, such as Klinefelter's syndrome. There are also minor DNA alterations called microdeletions, which can also affect male fertility.