Round cells in semen are of two types: immature sperm and white blood cells. To determine the percentage of white blood cells (specifically granulocytes) a special leukocyte screening test must be done. This test involves staining for the peroxidase enzyme present in the granulocytes.

The 1999 WHO manual contains a protocol for doing this test (Appendix III). There is also at least one test kit on the market for this assessment (Leukoscreen: Bioscreen, Inc.).

Laboratories with particular expertise in doing CBC and assessing granulocytes in stained blood smears may be able to do a differential count by this method rather than using a biochemical test for leukocyte screening.