KLK3 and prostate carcinoma: Furthermore, patients with low SDNN (<20ms) had significantly higher CEA at 1 year (p=0.006) and even at study entry than patients with higher initial SDNN. De Couck et al. [37] showed that SDNN and RMSSD were significant predictors of prostate-specific antigen (PSA) levels at 6 months in prostate cancer patients, controlling for numerous confounders (r=-0.434, p=0.004; r=-0.437, p=0.004, respectively).