Occult Faecal Blood Loss Determined by a51Cr Method and Chemical Tests in Patients Referred for Colonoscopy

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Abstract
In 67 patients referred for colonoscopy the fecal blood loss was determined by a 51Cr method and 7 chemical tests. For patients with negative colonoscopy (n = 10), colorectal polyps (n = 24), rectal cancer (n = 8) or colonic cancer (n = 12), the median 51Cr-determined fecal 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 fecal specimens before testing proved unimportant. Fecatwin sensitive showed more positive tests in delayed compared with immediate analyses (P < 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 .apprx. 85%, 85%, 85%, 80% and 45%, respectively. All chemical tests detected fecal blood loss from colorectal lesions more easily than from gastric lesions.