Occult-blood screening for colorectal carcinoma: the risks.

The evidence that occult-blood (Hemoccult) screening for colorectal carcinoma is beneficial has been examined in a companion paper. No data have yet been published demonstrating actual reductions in morbidity or mortality among patients undergoing the test. In this paper the risks of occult-blood screening are examined. It is shown that significant harm may result from the test's widespread application, due to the need for extensive endoscopic and radiological investigations in persons with a positive result (the vast majority of whom will subsequently be found not to have cancer). Furthermore, the most favorable benefit-risk ratio in Hemoccult screening (i.e., the highest positive predictive value for cancer) is found among persons over 70 years of age. Yet they are generally the least likely of patients screened to undergo treatment if a cancer is found. It is concluded that the risks of occult-blood screening could outweigh the benefits of any age group.