Perception errors with double-contrast enema after a positive guaiac test.

Between 3 and 6 of 12 colorectal neoplasms larger than 1 cm in diameter were overlooked by each of 4 radiologists in 117 individuals investigated with double-contrast enema (DCE) after a positive guaiac test. Even when the individual results of 2, 3, or 4 experienced radiologists were combined, 2 small carcinomas were overlooked due to perception errors. One of these carcinomas was diagnosed by rectosigmoidoscopy, which is an important and necessary complement to DCE. Although small carcinomas may be missed even with this combination, meticulous exploitation of the 2 methods is absolutely necessary to minimize the risk of missing a colorectal neoplasm. A drawback when 2 or more radiologists read the radiographs is the increased number of false-positive findings.