C3 in seminal plasma has no additional informative value in the diagnosis of infection/inflammation of the male genital tract.

The objective of this study was to determine the clinical significance of complement fraction C3 (C3c) in seminal plasma. Therefore 120 samples from randomly chosen subfertile males without signs of genital tract infection were screened for C3 and for seminal leucocytes as markers for subclinical infection/inflammation. A comprehensive semen evaluation included sperm analysis, sperm migration testing, immunocytochemical round cell differentiation to determine seminal leucocyte counts and the leucocyte ratio and semen cultures, in aliquots of the same ejaculates. C3 concentrations were significantly correlated with leucocyte counts per ml (P < 0.002) and per ejaculate (P < 0.001), and with the leucocyte ratio (P < 0.001). No association of C3 concentrations with semen quality or with the bacterial colonization of semen samples was found. The significant association with seminal leucocytes suggests that C3 might be used as an additional marker for silent male genital tract infection. In comparison with semen leucocytes, C3 screening does not reveal any further information about semen quality or infection/inflammation pathogenesis of the male genital tract.