When a semen analysis o seminogram is performed, one of the examinations included is the analysis of the presence of leukocytes in semen. It allows a more accurate examination of what is causing male infertility to be done, although it is commonly related to infections.
The presence of leukocytes in the sperm is a symptom of an infection that may cause male sterility, which may be temporary. The infection must be treated, so that sterility doesn’t become irreversible.
When taking about male sterility due to a post-testicular factor, what is meant are alterations in the spermatozoa once they’ve been produced in the testicles. They can be caused by problems in the displacement through the vasa deferentia.