KLK3 and sexually transmitted disease: The possible explanation for that is the large age range of patients (18–50 years), elusive temporal factor (it is virtually impossible to distinguish between recent and old infection because a large proportion of cases are asymptomatic; time frames between urethral and prostatic infection, prostatic infection and blood PSA response), high variability in the PSA value (partly because of large age range) and possibly, the factor of prostate volume (higher PSA values in patients with larger prostate), and the low number of STI-positive patients.