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Occult blood in the stool may be the first sign of otherwise asymptomatic colorectal cancer or other gastrointestinal disease. All patients over 40 should therefore have a rectal examination that includes a Hemoccult slide test. A rational diagnostic plan is essential to identify the source of occult blood in the stool. Most gastrointestinal cancer is operable if diagnosed early, so early detection of these lesions is imperative.
In a female patient with unexplained anemia, ascorbic acid ingestion and apparent false-negative occult blood tests were related. When she stopped ascorbic acid, her stools became strongly reactive ("4+") by three tests for occult stool blood; this association was observed repeatedly. A test developed to measure stool occult blood in the presence of ascorbic acid remained reactive throughout this observation, and the observation was confirmed by in-vitro studies. Current tests for occult blood depend on the pseudoperoxidase activity of heme and are inhibited by low levels of ascorbic acid. Reducing substances chemically similar to ascorbic acid also inhibits occult blood tests; oxidized ascorbic acid and sulfhydryl reducing agents do not inhibit them at physiologic levels.
A screening program for colorectal cancer and adenomas has been applied to 6,579 mostly asymptomatic men and women age 40 years and older utilizing fecal occult-blood testing followed by investigation of patients with positive slides by air-contrast barium enema and colonoscopy. A control population of 7,325 patients had sigmoidoscopy only and no occult-blood testing. Approximately 1% of the patients had positive slides; most patients had only one or two slides positive. Approximately 50% of patients with positive slides had significant neoplastic lesions, including 23 patients with large adenomas and 7 patients with cancers. Pathological staging of cancers was more favorable in the screened asymptomatic group as compared with the control group. Neoplastic lesions seen on sigmoidoscopy in screened patients who had negative fecal occult-blood tests included 2 cancers and 15 large adenomas. Reasons for false negativity include possible conversion of initially positive slides to negative. Screening for colorectal cancer and adenomas with fecal occult-blood testing appears to be feasible approach with good patient compliance, and manageable rate of positive slides productive of a high percentage of neoplastic lesions. The number of false-positives seems to be low. False negativity has been observed and will require further study.
Inhibition of anti-Rh29 by erythrocytic stroma in feces was devised as a specific test for fecal occult blood. The sensitivity of this test was equivalent to that of a standard Hemoccult test, namely, 10(8) erythrocytes/g feces. Comparison of results of this test with results of Hemoccult tests of random stool specimens and of stools following ingestion of autologous blood revealed nonuniform distribution of occult blood in feces. The extent of nonuniformity was determined by testing samples of stool specimens following ingestion of 51Cr-labeled autologous blood. This allowed comparison of Hemoccult, inhibition of anti-Rh, and radioactivity, and showed that the three labels could separate in the feces and that some single small samples of feces could be relatively free of blood while blood was readily demonstrable in other portions. The variability of standard Hemoccult test was somewhat reduced by dispersing the feces in distilled water before performing the test.
Peroheme 40, a chemical test for occult blood in faeces, has been assessed by comparing it with results obtained using 51Cr labelled red cells. The study was carried out in two parts. Initially testing was carried out on 75 stool samples from 20 patients on a restricted diet, and in the second part, testing was performed on 40 samples from 10 patients on a normal ward diet. All patients were suspected of losing blood from the gastrointestinal tract. On the restricted diet there were 29 per cent false positive and 13 per cent false negative results, while on the normal diet, there were 86 per cent false positive and 8 per cent false negative results. Peroheme-40 has therefore been shown, on a restricted diet, to compare favourably with previously available chemical tests.
In families with one of the Mendelian hereditary polyposes, one can predict the proportion of patients at risk and thus obtain a denominator against which colonoscopy, barium enema, and fecal occult blood can be validated. Colonoscopy is more sensitive than barium enema. There were 42 positive colonoscopies, 12 positive barium enemas, both being positive in 10 of these. There were 141 negative enemas, 133 negative colonscopies, and 118 negative for both. Occult blood was positive in 30% of patients with polyposis, five to seven times more frequently than in those without evident polyposis. Colonoscopy detected polyposis in 30% of the progeny of affected people. The shortfall, compared with the 50% expected under the Mendelian hypothesis, is readily explained by removal of affected cases from the study by surgery or death from cancer.
1000 patients of a proctological practice were all investigated by coloscopy and parallel to this by comparison of the two tests for occult blood in the stool (Haemoccult and hemo FEC). 5,6% were positive by the Haemoccult test, 5,2% to hemo FEC. There was no significant difference between the two systems. In the entire study 13 carcinomata and 39 benign polyps of 5 mm diameter and more were found, 8 patients with carcinoma had a positive hemo FEC test, 7 had a positive Haemoccult test, i.e. 38% of carcinoma patients were not detected by the hemo FEC test and 46% in the Haemoccult test. Even in patients with somewhat larger polyps, the test for occult blood in the stool was negative in 56%. It is pointed out with reference to two separate patients that in individual cases of even advanced carcinoma of the large intestine no blood can be detected in the stool.
Due to the high frequency and usually late diagnosis of cancer of colon and rectum the "haemoccult test" has been recommended as an easy, quick, and unexpensive method for stool determination of occult blood that will allow us to suspect the existence of these tumors in their early asymptomatic stages. The test was performed in 1437 patients attending the gastroenterology clinic which had no clinical evidence of bleeding, of these, 1150 returned the samples. In 52 (4,6%) the test was positive for occult blood. The studies performed revelated that 4 were upper gastrointestinal ilions, one ileal diverticulum and 40 (3,47%) patients had colonic disease of the latter 19 were diverticular disease, 1 crohnis disease of rectum, 2 adenomatous and 2 villous polips, 1 Hodkgin disease and 7 carcinomas. There were 6 false positive results. The high frequency of positive "haemoccult test" in colonic disease, specially benign and malignant tumors, make this test and appropiate method of this time in the detection for colo-rectal carcinoma.
Results from the quaiac slide or Hemoccult (HO) test for fecal occult blood were compared with quantitative determinations of gastrointestinal loss after intravenous administration of 51Cr-labeled red cells. Subjects were 80 consecutive patients, without dietary restriction, who were referred because of clinical suspicion of gastrointestinal blood loss or complex anemia. A total of 555 stool specimens analyzed for 51Cr loss were graded negative, trace, or positive by the HO method. Of 338 specimens containing 0-2 ml/day by isotope assay, 7.4% were positive to the HO qualitative test. Loss of at least 10 ml/day in 51Cr equivalent was necessary to assure that the majority of HO reactions would be positive. Of specimens containing more than 30 ml/day, 93% were positive. The ratio of 51Cr-labeled red cell equivalents to stool volume and the percentage of positive HO reactions increased together. When this ratio exceeded 10%, two thirds of the HO responses were positive.
A new stool occult blood test is described with improved sensitivity (more true positives) and specificity (fewer false negatives; more true negatives) than other clinically available procedures. The procedure chemically separates heme from globin and extracts heme into ethyl acetate, where a colorimetric reaction gives semiquantitative estimation of hemoglobin. The test is based on the retention of heme pseudoperoxidase activity in the ethyl acetate. Specifically, peroxide is degraded by heme to superoxide radicals which oxidize a chromophore to a colored compound. Various diamino and other chromogens are evaluated, and a new reagent, the noncarcinogenic diamino compound TMB is recommended for routine use. False positives may account for two thirds of all positives in routine screening. In addition, special diets and time delays due to dietary restrictions are avoided in this test. The test is also inexpensive and easy to perform. A technologist can perform 30 or more tests per hour.
Stool samples of 150 unselected patients were tested for occult blood by the Haemoccult test and the Fecatest. The results show that the Haemoccult test is more suitable for screening for cancerous and precancerous colonic lesions than the Fecatest. Less than 10% of the patients had positive stool samples with the Haemoccult test, while bleedings lesions were subsequently found in about 2/3 of the cases. In contrast, the Fecatest was positive in 50% and in 70% after storage. These findings show clearly that the Fecatest cannot be recommended for the screening of colonic tumors.
The clinical significance of the laboratory information provided by Fecatest, a new test based on a guaiac reaction for detecting occult blood in the feces, has been determined. In 93.8% of 243 patients with a lesion of the gastrointestinal tract diagnosed by endoscopy and/or radiology the test was positive; 88.5% of 148 patients in whom no lesion had been found by the same methods had a negative test. In vivo and in vitro comparison of the degree of sensitivity of Fecatest with Hematest and Haemoccult showed the following ratios: Hematest 5, Fecatest 3, Haemoccult 1. In point of sensitivity Fecatest thus comes between the other two tests investigated. It is concluded that Fecatest is a valuable tool in detecting lesions of the gastrointestinal tract associated with occult bleeding. The results show a better degree of clinical correlation between the test and the lesions in the gastrointestinal tract than with the other two. This view is further strengthened by the important practical advantages offered by Fecatest.
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.
Using Heglostix-Ames test strips, it was possible with normally fed animals, to furnish evidence of occult blood in spontaneous droppings of mice. The mice were exposed either to partial irradiation encompassing the abdomen and using different exit doses between 100 R and 1100 R, or were injected intramuscularly with doses between 120 and 900 mg/kg Endoxan or, instead, 110 and 840 mg/kg Proreside. The moment of the beginning and also the duration of positive reactions could be proved to depend on the dose. In simultaneous as well as alternating radiation- and chemotherapy evidence was given of cumulation effects. Reactions were always negative in nontreated controls.
Cancer of the large bowel is an important cause of morbidity and mortality. The barium enema is still the most reliable diagnostic tool, but the selection of the proper candidates for this moderately expensive and time-consuming examination presents a real problem. To wait for significant symptoms of change in bowel habits, such as unexplained anaemia, is hazardous. Testing for occult blood has fallen into disuse in most general practices. This paper discusses some of the available techniques for this procedure which I suggest offer a worthwhile aid to examination of patients with possible alimentary neoplasm.
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