Whether pus cells are present or not. While a few white blood cells in the semen is normal, many pus cells suggests the presence of seminal infection. Unfortunately, many labs cannot differentiate between sperm precursor cells ( which are normally found in the semen) and pus cells. This often means that men are overtreated with antibiotics for a "sperm infection" which does not really exist ! Some labs use a computer to do the semen analysis. This is called CASA, or computer assisted semen analysis. While it may appear to be more reliable (because the test has been done "objectively" by a computer), there are still many controversies about its real value, since many of the technical details have not been standardised, and vary from lab to lab.