KLK3 and prostatitis: However, inthe present study, a significant positive correlation was observed betweenpostmortem serum PSA levels and age after excluding cases of prostatic disease.Regarding the cause of an increase in serum PSA levels with age, Oesterling et al.17 suggested that this increase is caused by enlargement of prostate volumeor an increase in permeability for PSA in ductal epithelium cells of theprostate.