Prostate-specific antigen test: operating characteristics and assessment criteria in the diagnosis of prostatic cancer.

The sensitivity and specificity of prostate-specific antigen (PSA) in prostatic carcinoma is of considerable interest. In this study, we have assessed PSA and also correlations between positive and negative predictive values of PSA and the prevalence of prostatic cancer. Firstly, cutoff point must be selected as a positivity criterion for prostatic cancer, according to the purpose of the test. Besides sensitivity, all the other operating characteristics are dependent upon the prevalence of the disease. Specificity and positive predictive value increase while negative predictive value decreases when prevalence increases. As the relationship between the age and the prevalence of prostatic carcinoma is well known, the age of the patient becomes a variable of prominent importance when assessing the test.