Effect of bowel cleansing and colonoscopy on serum CEA levels.

A group of patients being investigated for various forms of colonic pathology showed an apparent rise in serum carcinoembryonic antigen (CEA) level following bowel cleansing at the time of colonoscopy, as compared with the 'resting' level. The rise was particularly marked in a small group of patients with colonic polyps or previous colonic resection for carcinoma, suggesting a need for careful timing in the taking of blood samples. The findings may also have diagnostic importance in identification of patients at higher risk of malignant disease of the colon.