Occult faecal blood loss determined by a 51Cr method and chemical tests in patients referred for colonoscopy.

In 67 patients referred for colonoscopy the faecal blood loss was determined by a 51Cr method and 7 chemical tests. For patients with negative colonoscopy (no. = 10), colorectal polyps (no. = 24), rectal cancer (no. = 8), or colonic cancer (no. = 12), the median 51Cr-determined faecal blood loss was 0.67, 0.74, 1.26, and 2.18 ml/24 h, respectively. For all chemical tests the results were highly influenced by the upper time limit for a positive reaction. Mixing of faecal specimens before testing proved unimportant. Fecatwin sensitive showed more positive tests in delayed compared with immediate analyses (p less than 0.01). Of cases of colorectal polyps, tetramethylbenzidine (TMB) tests including Hemo-Fec Test could detect half, the benzidine test 2 of 5. Fecatwin sensitive and Hemoccult II 1 of 4, and Fecatwin 1 of 24. Of cases of colorectal cancer, TMB tests, the benzidine test, Fecatwin sensitive, Hemoccult, and Fecatwin could detect about 85%, 85%, 85%, 80%, and 45%, respectively. All chemical tests detected faecal blood loss from colorectal lesions more easily than from gastric lesions.