Hemoccult Screening in Detecting Colorectal Neoplasm: Sensitivity, Specificity, and Predictive Value

Study objective To determine the sensitivity, specificity, and predictive value of Hemoccult II tests for detecting colorectal neoplasm (colorectal carcinoma or polyp or both). Study design Prospective analyses of asymptomatic patients (greater than or equal to 45 years) followed for 4 years after screening with Hemoccult II testing and retrospective analyses of patients, with known colorectal carcinoma or polyps or both who had Hemoccult II testing within 2 years of diagnosis. Setting A large, health maintenance organization practice. Measurements and main results In the prospective analysis, the sensitivity of Hemoccult II was 50% for colorectal carcinoma diagnosed within 1 year of testing, 43% within 2 years, and 25% within 4 years. For polyps, sensitivity was 36% at 1 year, 28% at 2 years, and 17% at 4 years. Specificity was 99%. The predictive value of a positive test for colorectal carcinoma was 8% at 1 year, 10% at 2 years, and 11% at 4 years. On the basis of the retrospective analyses, the sensitivity of Hemoccult II for colorectal carcinoma diagnosed within 1 year of testing was 66% and was 61% within 2 years. Many of these patients had symptoms when tested. Conclusions An asymptomatic patient age 45 or older with a positive Hemoccult II test has about a chance of 1 in 10 for having colorectal carcinoma and a 1-in-3 chance of having either a colorectal carcinoma or polyp: The same patient with a negative Hemoccult test has a 0.2% chance of having a colorectal carcinoma diagnosed within 2 years of testing and a 0.7% chance of having a polyp. Within 4 years of testing the chance increases to 0.5% for colorectal carcinoma and 1.5% for polyps. If Hemoccult II slides are the only screening method used for detecting asymptomatic colorectal neoplasms, 50% to 60% of lesions will remain undetected. Clinical interpretation of Hemoccult screening requires appreciation of its limits as well as its benefits.