How to perform the fecal occult blood test

The history of colorectal cancer screening: a personal perspective

The present explosive interest in screening for colorectal cancer (CRC), one of the most prevalent and preventable cancers, had its beginnings at a hospital in London and an Internist's office in Ohio. Demonstrated there were the concepts that CRC did not occur de-novo but arose from a premalignant polyp, that detection of the resultant cancer at an earlier stage was associated with better survival and that cancer could be detected at an early presymptomatic stage by screening. Many years later, the introduction of colonoscopy and colonoscopic polypectomy provided the opportunity for randomized trials to prove that these concepts were true. The sequence of rigorous science followed by guidelines consensus and then multilevel national efforts of screening implementation has resulted in a decline in the CRC incidence and mortality worldwide, most significantly in the USA. Campaigns have been initiated to maximize population screening and further investigate its optimal approach. Some historical details of this success story and many of the key participants are presented in this paper.

Evaluation of the sensitivity and specificity of four laboratory tests for detection of occult blood in cockatiel (Nymphicus hollandicus) excrement

OBJECTIVE

To compare sensitivity and specificity of cytologic examination and 3 chromogen tests for detection of occult blood in cockatiel (Nymphicus hollandicus) excrement.

ANIMALS

20 adult cockatiels.

PROCEDURES

Pooled blood from birds was divided into whole blood and lysate aliquots. Excrement was mixed with each aliquot in vitro to yield 6 hemoglobin (Hb) concentrations (range, 0.375 to 12.0 mg of Hb/g of excrement). For the in vivo portion of the study, birds were serially gavaged with each aliquot separately at 5 doses of Hb (range, 2.5 to 40 mg/kg). Three chromogen tests and cytologic examination were used to test excrement samples for occult blood. Sensitivity, specificity, and observer agreement were calculated.

RESULTS

In vitro specificity ranged from 85%to 100% for the 3 chromogen tests and was 100% for cytologic examination. Sensitivity was 0% to 35% for cytologic examination and 100% for the 3 chromogen tests on samples containing >or= 1.5 mg of Hb/g of excrement. In vivo specificity was 100%, 90%, 65%, and 45% for cytologic examination and the 3 chromogen tests, respectively. Sensitivity was 0% to 5% for cytologic examination and >or= 75% for all 3 chromogen tests after birds received doses of Hb >or= 20 mg/kg. Observer agreement was lowest for cytologic examination.

CONCLUSIONS AND CLINICAL RELEVANCE

Chromogen tests were more useful than cytologic examination for detection of occult blood in cockatiel excrement. The best combination of sensitivity, specificity, and observer agreement was obtained by use of a chromogen test.

Rationale for combining different screening strategies

It is generally accepted that screening programs should be quite safe, and that the benefits should substantially outweigh the harms. As Cochrane and Holland stated: We believe that there is an ethical difference between everyday medical practice and screening. If a patient asks a medical practitioner for help, the doctor does the best he can. He is not responsible for defects in medical knowledge. If, however, the practitioner initiates screening procedures he is in a very different situation. He should, in our view, have conclusive evidence that screening alters the natural history of disease in a significant proportion of those screened. If this is so, one should recommend the combination over either test alone only if there is sufficient evidence that the combination is more effective and no more dangerous. There is a difference of opinion over whether the evidence, which is certainly not strong, is nevertheless sufficient. This poses a dilemma. Many expert groups prefer that screening for colorectal cancer be done with both FOBT and sigmoidoscopy rather than either alone. Yet, the strength of the evidence for additional effectiveness, and information on the magnitude of that effect if it is present, is substantially less than for the individual tests. This being the case, the author believes that it is premature to advocate the combination over either test alone, especially when the most pressing national priority in colorectal cancer screening is to get a large proportion of the adult population to be screened at all.

Early detection for colorectal cancer: new aspects in fecal occult blood screening

The authors report on promising diagnostic methods of occult intestinal bleeding and discusses the potential new strategy of early detection of colorectal carcinomas in respect to old and new diagnostic measures available. Because of the limited sensitivity and specificity of classical methods used for the demonstration of occult fecal blood, the authors recommend the introduction of new techniques and markers in screening practice. It is presumed that new discoveries in molecular biology will improve the accuracy of early colorectal cancer prevention. Their implementation into routine screening, however, will not take place in the near future. Until their realization, improved screening efficacy is expected from the use of more specific and sensitive blood tests.

Colorectal neoplasms

Preview Colorectal neoplasms occur in many forms, but two are of primary clinical significance to physicians-adenoma and adenocarcinoma. Among the challenges these lesions present are accurate diagnosis, effective therapy, practical and affordable screening and surveillance, and primary prevention. Of key importance in designing workable management strategies is identification of factors that define higher-risk patient groups.

Evaluation of new occult blood tests for detection of colorectal neoplasia

BACKGROUND

Hemoccult II, the guaiac-based fecal occult blood test used in most colorectal cancer screening programs, has an unsatisfactory sensitivity for asymptomatic colorectal neoplasms. We evaluated the relative performance of four fecal occult blood tests, directed against various components of the hemoglobin molecule.

METHODS

All tests, Hemoccult II, HemoccultSENSA (a more sensitive guaiac test), HemeSelect (an immunochemical test specific for human hemoglobin), and HemoQuant (the heme-porphyrin assay), were performed by 107 patients with symptomatic colorectal cancer and 81 patients with predominantly asymptomatic adenoma. Hemoccult-SENSA and HemeSelect were performed by 1,355 screenees.

RESULTS

HemeSelect and Hemoccult-SENSA had significantly higher sensitivity for colorectal cancer (97% and 94%, respectively) than the other tests. HemeSelect had the highest sensitivity for adenomas; in 45 patients with large (> or = 10 mm) adenomas, sensitivity was 76% for HemeSelect, 60% for HemoccultSENSA, and 42% for both Hemoccult and HemoQuant. In the screenees, estimated specificity was 97.8% for HemeSelect and 96.1% for Hemoccult-SENSA.

CONCLUSIONS

HemeSelect and Hemoccult-SENSA have the highest levels of sensitivity for detection of colorectal neoplasia, but the immunochemical test HemeSelect provides the best combination of specificity and sensitivity.

The National Polyp Study. Design, methods, and characteristics of patients with newly diagnosed polyps. The National Polyp Study Workgroup

The National Polyp Study (NPS) is a multicenter prospective randomized trial designed to evaluate follow-up surveillance strategies in patients who have undergone polypectomy for the control of large bowel cancer. The study design was developed by a joint research committee from American Gastroenterological Association, the American Society for Gastrointestinal Endoscopy, and the American College of Gastroenterology. Subjects who met the eligibility criteria were randomized into two different treatment arms. Eligibility criteria included: removal of one or more adenomas; complete colonoscopy; no prior polypectomy, inflammatory bowel disease, or familial polyposis; and no history of colon cancer. The treatment arms consisted of a frequent follow-up (1 and 3 years after initial polypectomy) and a less frequent follow-up (3 years). Follow-up examinations included fecal occult blood tests, air-contrast barium enema, and colonoscopy. The latter was done on 9112 referred patients at the seven participating centers from November 1980 until February 1990 who had no history of polypectomy, colon cancer, familial polyposis, or inflammatory bowel disease. Of these patients, 4763 (52.3%) had no polyps; 549 (6.0%) had an invasive cancer; 776 (8.5%) had nonadenomatous polyps; 208 (2.3%) had incomplete examinations; 184 (2.0%) had other findings; and 2632 (28.9%) had one or more adenomas, of which 1418 (53.9%) were randomized to one of the two treatment arms. This article reports the background, rationale, objectives, methods, and organization of this study and includes patient characteristics on initial presentation. Future data provided by the NPS may help in the development of recommendations for surveillance guidelines for such patients. This study also provides a framework to address questions regarding the natural history of adenomas and their relationship with colorectal cancer.

Compliance with fecal occult blood testing: the role of restrictive diets

In this clinical trial, 786 patients screened for colorectal cancer with fecal occult blood testing were assigned to either a "diet" or "no diet" group to examine the effect of advice to restrict intake of red meat and peroxidase-containing vegetables on patient compliance and positivity rates. Restrictive diets did not significantly decrease compliance. Interviews of patients in the "diet" group demonstrated that the majority followed instructions. Positivity rates were similar in the two groups, and clinically significant lesions were found with comparable frequency.

Effect of oral iron therapy on the upper gastrointestinal tract. A prospective evaluation

This study assesses the effect of oral iron therapy on the upper gastrointestinal tract and fecal occult blood testing. Fourteen healthy volunteers completed a checklist of gastrointestinal symptoms, underwent endoscopy and biopsy of the stomach and duodenum, and supplied a fresh stool sample for Hemoccult and HemoQuant testing. They then took ferrous sulfate 325 mg per os tid for two weeks and had the same evaluation repeated. Gastrointestinal symptoms were rated by the patients on a scale of 0-3, endoscopic findings were numerically scored (0-4), and the biopsies were graded blindly. Thirteen other healthy volunteers took ferrous sulfate 325 mg per os tid for one week and had Hemoccult testing of stool at days 0 and 7. All subjects developed dark stools, and significant nausea and diarrhea were noted (0.1 +/- 0.1 to 0.9 +/- 0.3, P less than 0.05 for both symptoms). Only 1/27 had a questionably trace-positive Hemoccult test (two observers disagreed) and no significant difference was seen in HemoQuant testing (1.4 +/- 0.5 to 1.8 +/- 0.7 mg Hb/g). A significant increase was seen in endoscopic abnormalities in the stomach (0.1 +/- 0.1 to 1.5 +/- 0.3, P = 0.003), consisting of erythema, small areas of subepithelial hemorrhage, and, in two subjects, erosions. Biopsies showed no significant change after iron therapy. We conclude that (1) oral ferrous sulfate rarely causes Hemoccult-positive stools, and patients with positive Hemoccult tests on iron therapy require further evaluation; and (2) oral iron may cause mild endoscopic abnormalities in the stomach which are of uncertain clinical significance.

Screening of colorectal cancer

Colorectal cancer (CRC) remains a cancer in a disappointing location. However, its location clearly has an advantage that could theoretically permit efficient secondary prevention: the preceding of the cancer by a benign lesion, ie, the adenoma. Complete colonoscopy and its substitute, the double-contrast barium enema, and their specific limitations, must be reserved for high-risk patients: hereditary cancers and ulcerative colitis. For all the others, ie, adults of 45 years of age and with standard risks, the proposal is either to select the patients to be colonoscoped through occult blood testing of the stools or to perform a fiber sigmoidoscopy or a combination of both. Although imperfect, both methods allow the detection of polyps and cancers at a presymptomatic stage, when they are either benign or malignant, but localized and with a better prognosis. However, the absolute proof of the benefits of this strategy of screening would be the demonstration by controlled studies of a prolonged survival rate or a decrease in morbidity. Until now, this proof is not fully available.