WHAT IS THE NORMAL RANGE FOR PROSTATE-SPECIFIC ANTIGEN - USE OF A RECEIVER OPERATING CHARACTERISTIC CURVE TO EVALUATE A SERUM MARKER

Objective To compare the relative sensitivity and specificity of prost ate-specific antigen (PSA) as a test for prostate cancer over a range of PSA values in a variety of patient groups, and to compare the sensi tivity and specificity of PSA and prostatic acid phosphatase (PAP). Su bjects and methods Receiver operating characteristic (ROC) curves (sen sitivity plotted against 1-specificity) were constructed to compare th e ability of PSA to discriminate men with prostate cancer (n = 257) fr om those with benign prostatic hyperplasia (BPH) (n = 220) or control patients (n = 164). Receiver operating characteristic curves were also constructed to compare PSA and PAP in 173 men with either BPH or pros tate cancer. Results When patients with symptomatic BPH and those with advanced prostate cancer are excluded, a PSA of 8 ng/mL has a sensiti vity of 94% and a specificity of 98% for prostate cancer, In patients presenting with symptoms suggestive of bladder outflow obstruction, PS A remains a sensitive marker for prostate cancer (93% sensitivity at 1 0 ng/mL) but its specificity (65%) is poor. PSA is a sensitive test fo r skeletal metastases but levels of 60-80 ng/mL are required to achiev e a specificity of 7O% or more. The sensitivity of PSA is far superior to that of PAP. Conclusion Serum PSA provides good discrimination bet ween patients with and without prostate cancer, The sensitivity and sp ecificity of PSA can be improved by excluding men with symptomatic BPH . The specificity of PSA as a diagnostic test for prostate cancer is r educed in men with symptoms of bladder outflow obstruction. For reason able sensitivity and specificity, a PSA of 60-80 ng/mL, is required fo r differentiating non-metastatic from metastatic prostate cancer. The ROC curve comparing PSA and PAP provides a graphical demonstration of the superiority of PSA as a tumour marker. The ability of PSA to ident ify prostate cancer can be improved by selecting out groups of patient s and by adjusting the cut-off level of PSA to the population under st udy.