Measurement of protein C inhibitor in seminal plasma is useful for detecting agenesis of seminal vesicles or the vas deferens.

Protein C inhibitor (PCI), a plasma serine protease inhibitor of activated protein C, is present at high concentrations in the seminal plasma of normal subjects and is decreased in some infertile patients. We measured the concentrations of PCI, prostate-specific antigen, and fructose in the seminal plasma of infertile patients (n = 125) and of normal subjects (n = 13). We also measured time-dependent changes in the concentrations of PCI and fructose in seminal plasma after ejaculation. A weak correlation was found between the levels of PCI and fructose (r = 0.268, P = 0.016). The PCI level in seminal plasma of patients with seminal vesicle and/or vasal agenesis was significantly lower (P < .01) than in normal subjects. The level of fructose in seminal plasma decreased in vitro in a time-dependent manner after ejaculation, whereas the concentration of PCI was stable at 48 hours after ejaculation. These data suggest that PCI in seminal plasma, as well as fructose, may become one of the markers for agenesis of seminal vesicles and/or the vas deferens.