ASSESSMENT OF ROUTINE TESTS FOR OCCULT BLOOD IN FAECES

Reducing disparities and achieving health equity in colorectal cancer screening

Increases in colorectal cancer screening are linked to the declining incidence of the disease over the past three decades. These favorable trends, however, are not observed in marginalized racial and ethnic populations with disproportionately lower rates of screening, higher disease incidence, and increased mortality despite advances in health technology and policy. This review describes the differences in screening uptake and test selection amongst racial and ethnic groups, discusses known obstacles and facilitators that impact screening, and highlights existing frameworks developed to achieve health equity in colorectal cancer screening.

Sensitivity of fecal occult blood testing in the cat

Objectives

The impact of dietary factors on fecal occult blood (FOB) testing has been previously evaluated in cats, but the analytical sensitivity of this point-of-care test remains unexamined. The primary goal of this study was to assess the analytical sensitivity of the FOB test in cats.

Methods

Five cats were used in a repeated measures study. Following oral administration of blood, feces were collected and tested every 12 h for FOB and melena. All cats were fed an animal protein-free diet starting the week before entry into the study. Blood was administered on a milligram of hemoglobin per kilogram of body weight basis, and dosed at 1.5, 3, 15, 30 and 45 mg/kg hemoglobin in series with a wash-out period between each trial.

Results

FOB was detected in one cat at 1.5 mg/kg hemoglobin, three cats at 3 mg/kg hemoglobin and in all five cats at 15, 30 and 45 mg/kg hemoglobin. Melena was noted in one cat at 30 mg/kg and four cats at 45 mg/kg, but not at lower doses.

Conclusions and relevance

Administration of 15 mg/kg hemoglobin (equivalent to about 1.5 ml blood) was sufficient for positive results in all cats. However, detection occurred with as little as 1.5 mg/kg hemoglobin. Thus, FOB has good analytical sensitivity in cats under appropriate clinical situations.

The clinical value of Haemoccult and Fecatwin in the detection of colorectal neoplasia in hospital and general practice patients

Four hundred and fifty asymptomatic general practice patients and 330 hospital inpatients had their stools tested for occult blood with the Haemoccult and Fecatwin methods. In general practice, 9/64 (14%) of patients with a positive result had a colonic neoplasm (three carcinomas, one Dukes' Stage A, two Dukes' Stage C, six adenomas) and in hospital 12/142 patients (8%) were found to have colonic tumours, (nine carcinomas, two Dukes' Stage A, two Dukes' Stage B, five Dukes' Stage C and three adenomas). The overall detection rates for colonic neoplasia were 2% in general practice and 3.4% in hospital. In 2 years of follow-up, none of the general practice patients have presented with colonic symptoms. Two hospital patients with colonic carcinomas produced negative tests with both methods. Out of the total of 21 colonic neoplasms, nine were detected by Fecatwin alone, but this trend in favour of the more sensitive test did not reach the 5% level of statistical significance. In contrast, the number of false positive results were significantly greater with Fecatwin than Haemoccult. From our data it would appear that the Fecatwin method warrants assessment in a full controlled trial of its value as a population screening test for colonic cancer.

Iron deficiency and iron overload

An up to date review of our knowledge of human iron metabolism is given including problems of iron balance, internal transport, and intracellular mechanisms. Current knowledge of the iron proteins is summarized and this background is used in discussing the pathophysiology of iron deficiency and overload, together with the internal derangements such as sideroblastic anemia which form much of the clinical practice associated with disorders of iron metabolism. The therapeutic approach to these problems will be described.

Colorectal cancer: knowledge and attitudes of doctors in Victoria

Successful introduction of screening for early colorectal cancer will depend, at least in part, on doctors' knowledge and attitudes. A 34-item questionnaire was sent to a random sample of one in five doctors in Victoria, with a final completion rate of 65%. The survey revealed gaps of knowledge, particularly about recognition of high-risk groups. Only 12% were aware of the degree of increased risk faced by first-degree relatives of patients with colorectal cancer and only 10% recognised the similar increase in risk for people with a history of resected colorectal cancer. While 73% of doctors order faecal occult blood tests, only 9% were aware that the more reliable quaiac method was used for their patients. Overall, 38% considered that faecal occult blood testing was a practical method for screening for colorectal cancer. Most of the doctors who accepted occult blood screening would follow up a positive test with digital rectal examination (80%) and barium enema (75%), but only 58% would want sigmoidoscopy performed and 34% colonoscopy. The diagnostic potential of digital rectal examination and sigmoidoscopy was over-estimated by half of the doctors surveyed. Recognition of subjects at high risk for colorectal cancer, and knowledge about the proper use, follow-up, and potential for screening of faecal occult blood tests need emphasis in medical educational programmes.

Screening for occult gastrointestinal bleeding in hospital patients

Stools have been tested for occult gastrointestinal bleeding in 278 outpatients and 170 hospital inpatients using the Haemoccult and Haemastix methods. Seventeen outpatients (6.1%) and 42 inpatients (24%) were positive with the Haemoccult technique. Thirty-three outpatients (11.9%) and 93 inpatients (54.7%) were positive with the Haemastix test. Following investigation of the Haemoccult-positive patients, only 2 cases (3.4%) were considered false positive. However, the false positive rate with Haemastix was 22.9% which is unacceptable in a screening test. Haemoccult may be useful as a screening test for asymptomatic general practice patients, but a test of greater sensitivity is needed for hospital patients.

Reliability of chemical tests for fecal occult blood in hospitalized patients

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.

Hemoccult detection of fecal occult blood quantitated by radioassay

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.

Assessment of Peroheme-40 for the presence of occult blood in the faeces

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.

Tests for occult blood

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.

Role of occult blood loss in anaemia after partial gastrectomy

The present investigation is a study of occult gastrointestinal blood loss in 20 anaemic postgastrectomy patients and 14 control subjects. One patient in the postgastrectomy group was found to be bleeding from undetected haemorrhoids. One patient in each group showed sensitivity to aspirin with greatly increased occult blood loss. The mean blood loss in 18 postgastrectomy patients with unexplained anaemia was 0.6 +/- 0.5 ml/day compared with 0.5 +/- 0.5 ml/day in 13 control subjects. Only two of the 19 anaemic postgastrectomy patients studied lost more than 2 ml blood/day. Aspirin blood loss in 18 postgastrectomy patients was 2.4 +/- 2.1 ml/day, compared with 2.6 +/- 2.7 ml/day in 13 controls. The pattern of aspirin blood loss is identical in both groups. All gastric biopsies obtained from nine patients with Polya gastrectomies showed changes of gastritis; some showed complete gastric atrophy and intestinal metaplasia. Occult gastrointestinal bleeding is not an important factor in the pathogenesis of anaemia after partial gastrectomy unless there is either stomal ulceration or a lesion completely unrelated to the partial gastrectomy. If occult bleeding is present after partial gastrectomy a careful search for the site of bleeding is indicated. Excessive intake of aspirin or increased sensitivity to aspirin was not shown to be a significant factor in the pathogenesis of the anaemia in this group of patients. However, because of the inability to augment iron absorption to compensate for blood loss, it would be inadvisable for the patient with a partial gastrectomy to take a high dosage of aspirin for long periods of time, unless aspirin-induced blood loss is measured and shown to be very low. Aspirin administered in low dosage is not contraindicated after partial gastrectomy.