Guaiac tests for detection of occult faecal blood loss in patients with endoscopically verified colonic polyps.

To evaluate the sensitivity of guaiac tests for colonic polyps, two tests were made on occult blood in faeces--Hemoccult II and Fecatwin-S--from 625 and 549 patients, respectively, referred for colonoscopy. Polyps were found in 212 and 194 patients, and these had one or more tests positive in 41% (Hemoccult II) and 48% (Fecatwin-S). The incidence of positive tests was greater for polyps situated in the transverse, descending, and sigmoid colon; for polyps with a stalk, villous elements, and dysplasia; and especially for large polyps. Although size was the most important factor for the bleeding tendency, at least one third of patients with polyps over 10 mm in diameter had no positive guaiac reactions. In patients at high risk of developing polyps, therefore, these tests cannot replace, but may well be supplementary to, radiography with double-contrast technique and colonoscopy.