“What causes leukocytes in sperm?”

The short answer is inflammation. You should be tested fo an infection as the cause of the inflammation. A visit to a urologist would help discern causes, including scar tissue, bio keg, etc.

Leukocytes in sperm is a reflection of some infective ideology most prominently within the prostate

Prostatitis

Overall, there are only a few causes of leukocytes which are white blood cells - possible evidence of inflammation - within semen itself. Certainly, if there is an active infection you may see leukocytes in semen, but the patients are generally symptomatic with lower urinary tract symptoms, prostate pain, problems urinating and or pain with ejaculation. But more commonly, you can find leukocytes in semen and there just isn’t a reasonable cause. Lastly, depending on the experience of the laboratory technician who did the same analysis, sometimes leukocytes are misinterpreted as white blood cells when in reality they are simply immature sperm cells.