Reliability of chemical tests for fecal occult blood in hospitalized patients

Abstract

In 39 hospitalized patients with suspected gastrointestinal bleeding and given intravenous 51Cr-labeled red cells, reactions of three chemical spot tests for fecal occult blood were compared with the "true" blood loss as determined by stool radioassay. Guaiac reagent and orthotolidine (Hematest) tablets were extremely sensitive, but yielded false-positive reaction rates of 72% and 76%, respectively on the 240 stool specimens compared. A modified guaiac test (Hemoccult) exhibited a false positive rate of 12%. Of the 27 patients entering the study due to positive guaiac or Hematest screening tests, 17 (63%) were not bleeding. Hemoccult, approximately 1/4 as sensitive as guaiac and Hematest, could miss lesions with low rates of bleeding unless multiple stools were tested. While barium had no effect, iron therapy or laxatives tended to lower both false-positive and false-negative reactions for all reagents. A positive Hemoccult test usually indicated significant gastrointestinal bleeding and would appear to be the test of choice provided at least 3 stools are tested to minimize false-negative results.

Comparison of a guaiac and an immunochemical faecal occult blood test for the detection of colonic lesions according to lesion type and location

“…In accordance with our results, several authors have observed that the sensitivity of the G-FOBT decreases as the amount of bleeding of the lesion increases (Morris et al, 1976;Stroehlein et al, 1976;Herzog et al, 1982;Ahlquist et al, 1985;Macrae and St John, 1987). As in other studies, in our population, the measured intensity of bleeding of invasive cancers was higher than that of high-risk adenomas (Levi et al, 2007;Ciatto et al, 2007).…”

Immunological detection of faecal occult blood in colorectal cancer

“…False negative results with Haemoccult still occurred in 10% after a 6-day test period. The most sensitive FOBTs all need a very strict peroxidase-free diet (Gnauck, 1974;Morris et al, 1976;Adlercreutz et al, 1978;. Because dietary restrictions seem to be difficult for patients to follow, even under controlled circumstances, as in our study, the human haemoglobin specific test appears to be mandatory in colorectal cancer screening.…”

The pros and cons of fecal occult blood testing for colorectal neoplasms

“…Commercial tests vary in chemical sensitivity. 'Physiologic' GI blood losses average about 0.6 ml daily [51,52], and values greater than 2ml/day (equivalent to about 2 mg Hgb/g stool) are generally accepted as abnormal [53,54]. The popular Hemoccult test has relatively low chemical sensitivity, as daily blood losses must exceed 20 ml for reliably positive results (80%-90% positivity); fecal losses in the 5-10 ml/day range are commonly missed [54][55][56][57][58].…”

“…'Physiologic' GI blood losses average about 0.6 ml daily [51,52], and values greater than 2ml/day (equivalent to about 2 mg Hgb/g stool) are generally accepted as abnormal [53,54]. The popular Hemoccult test has relatively low chemical sensitivity, as daily blood losses must exceed 20 ml for reliably positive results (80%-90% positivity); fecal losses in the 5-10 ml/day range are commonly missed [54][55][56][57][58]. Other seemingly similar commercial tests vary considerably in sensitivity compared to Hemoccult [57-60], and minor modifications in the Hemoccult test itself over the years have apparently influenced its capacity to detect blood [61,62].…”