A cut-off value of 30% of the α2,3-sialic acid percentage of PSA discriminated between high-risk PC and the groups of BPH, low-, and intermediate-risk PC, with a sensitivity of 85.7% and specificity of 95.5%, and an AUC of 0.97 (better than using tPSA or %fPSA in the diagnostic grey zone). The gene discussed is KLK3; the disease is benign prostatic hyperplasia.