Hemoccult detection of fecal occult blood quantitated by radioassay

Is it worthwhile to perform capsule endoscopy for asymptomatic patients with positive immunochemical faecal occult blood test?

BACKGROUND

The immunochemical faecal occult blood test (IFOBT) is widely performed for colorectal cancer screening, but the usefulness of IFOBT in the detection of disorders of the small intestine is unknown. The objective of this study was to investigate what proportion of IFOBT-positive subjects with negative colonoscopy and oesophagogastroduodenoscopy has pathologies of the small intestine detected by capsule endoscopy (CE).

METHODS

Between October 2008 and June 2010, asymptomatic IFOBT-positive patients with negative total colonoscopy and oesophagogastroduodenoscopy underwent CE. CE findings were classified into three categories: P0 (no abnormalities, or findings without potential for bleeding), P1 (findings with uncertain potential for bleeding), P2 and (findings with high potential for bleeding).

RESULTS

Fifty-three patients (37 males, 16 females; 52.1 ± 13.0 years) were included. There were no cases with P2, 19 cases with P1, and 34 cases with P0 (there were no abnormalities in 25 of 34 cases). As a result, lesions in the small intestine were detected in 28 cases. Additional examination was considered necessary for five patients after CE, but no abnormality was detected, and therapeutic intervention was not undertaken in any case. Caecal completion rate was 92.5%.

CONCLUSIONS

No significant pathologies of the small intestine were detected in asymptomatic IFOBT-positive cases with negative colonoscopy and oesophagogastroduodenoscopy. CE is of limited use in asymptomatic patients with positive IFOBT.

Evaluation and treatment of iron deficiency anemia: a gastroenterological perspective

A substantial volume of the consultations requested of gastroenterologists are directed towards the evaluation of anemia. Since iron deficiency anemia often arises from bleeding gastrointestinal lesions, many of which are malignant, establishment of a firm diagnosis usually obligates an endoscopic evaluation. Although the laboratory tests used to make the diagnosis have not changed in many decades, their interpretation has, and this is possibly due to the availability of extensive testing in key populations. We provide data supporting the use of the serum ferritin as the sole useful measure of iron stores, setting the lower limit at 100 microg/l for some populations in order to increase the sensitivity of the test. Trends of the commonly obtained red cell indices, mean corpuscular volume, and the red cell distribution width can provide valuable diagnostic information. Once the diagnosis is established, upper and lower gastrointestinal endoscopy is usually indicated. Nevertheless, in many cases a gastrointestinal source is not found after routine evaluation. Additional studies, including repeat upper and lower endoscopy and often investigation of the small intestine may thus be required. Although oral iron is inexpensive and usually effective, there are many gastrointestinal conditions that warrant treatment of iron deficiency with intravenous iron.

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

We investigated variations in sensitivity of an immunochemical (I-FOBT) and a guaiac (G-FOBT) faecal occult blood test according to type and location of lesions in an average-risk 50- to 74-year-old population. Screening for colorectal cancer by both non-rehydrated Haemoccult II G-FOBT and Magstream I-FOBT was proposed to a sample of 20 322 subjects. Of the 1615 subjects with at least one positive test, colonoscopy results were available for 1277. A total of 43 invasive cancers and 270 high-risk adenomas were detected. The gain in sensitivity associated with the I-FOBT was calculated using the ratio of sensitivities (RSN) according to type and location of lesions, and amount of bleeding. The gain in sensitivity by using I-FOBT increased from invasive cancers (RSN=1.48 (1.16–4.59)) to high-risk adenomas (RSN=3.32 (2.70–4.07)), and was inversely related to the amount of bleeding. Among cancers, the gain in sensitivity was confined to rectal cancer (RSN=2.09 (1.36–3.20)) and concerned good prognosis cancers, because they involve less bleeding. Among high-risk adenomas, the gain in sensitivity was similar whatever the location. This study suggests that the gain in sensitivity by using an I-FOBT instead of a G-FOBT greatly depends on the location of lesions and the amount of bleeding. Concerning cancer, the gain seems to be confined to rectal cancer.

Random comparison of guaiac and immunochemical fecal occult blood tests for colorectal cancer in a screening population

BACKGROUND & AIMS

Despite poor performance, guaiac-based fecal occult blood tests (G-FOBT) are most frequently implemented for colorectal cancer screening. Immunochemical fecal occult blood tests (I-FOBT) are claimed to perform better, without randomized comparison in screening populations. Our aim was to randomly compare G-FOBT with I-FOBT in a screening population.

METHODS

We conducted a population-based study on a random sample of 20,623 individuals 50-75 years of age, randomized to either G-FOBT (Hemoccult-II) or I-FOBT (OC-Sensor). Tests and invitations were sent together. For I-FOBT, the standard cutoff of 100 ng/ml was used. Positive FOBTs were verified with colonoscopy. Advanced adenomas were defined as >or=10 mm, high-grade dysplasia, or >or=20% villous component.

RESULTS

There were 10,993 tests returned: 4836 (46.9%) G-FOBTs and 6157 (59.6%) I-FOBTs. The participation rate difference was 12.7% (P < .01). Of G-FOBTs, 117 (2.4%) were positive versus 339 (5.5%) of I-FOBTs. The positivity rate difference was 3.1% (P < .01). Cancer and advanced adenomas were found, respectively, in 11 and 48 of G-FOBTs and in 24 and 121 of I-FOBTs. Differences in positive predictive value for cancer and advanced adenomas and cancer were, respectively, 2.1% (P = .4) and -3.6% (P = .5). Differences in specificities favor G-FOBT and were, respectively, 2.3% (P < .01) and -1.3% (P < .01). Differences in intention-to-screen detection rates favor I-FOBT and were, respectively, 0.1% (P < .05) and 0.9% (P < .01).

CONCLUSIONS

The number-to-scope to find 1 cancer was comparable between the tests. However, participation and detection rates for advanced adenomas and cancer were significantly higher for I-FOBT. G-FOBT significantly underestimates the prevalence of advanced adenomas and cancer in the screening population compared with I-FOBT.

Carbonic anhydorase isoenzyme I (CA-I) concentration in feces and urine as a temporary marker of occult blood in beagle dogs

This study was undertaken to investigate whether the concentration of carbonic anhydorase isoenzyme I (CA-I) in canine feces and urine is useful as a temporary marker of occult blood. Concentrations of CA-I were measured by enzyme-linked immunosorbent assay (ELISA). Fecal CA-I concentrations in 113 healthy beagle dogs (50 male and 63 female) of various ages ranged from 4.3 to 16.7 ng/g feces (mean; 7.0 +/- 2.9 ng/g feces). One milliliter of blood from 3 healthy beagle dogs was found to contain 1,047, 1,062 and 1,150 microg CA-I. The fecal CA-I concentrations of dogs receiving intragastric infusions of autologous blood (10 ml) were very low. However, the fecal CA-I concentrations of dogs receiving infusion of autologous blood (5 ml) into the ascending colon were very high. Detection of fecal CA-I would be useful for identifying dogs with hemorrhaging of the large intestine. Of 55 urinary samples collected from healthy beagle dogs by catheter, chemical tests for occult blood were negative in 44, but CA-I concentrations ranged from 1.8 to 12.6 ng/ml (mean; 6.9 +/- 5.4 ng/ml) by ELISA. The CA-I concentrations of the other 11 samples, which tested positive for occult blood on chemical testing, ranged from 41.2 to 525.0 ng/ml by ELISA. Although CA-I is not a specific marker of erythrocytes, CA-I may be used to detect occult blood in canine feces and urine until a specific immunological test kit using antibody for Hb is developed.

Effective screening for bowel cancer: a United kingdom perspective

Bowel cancer is a major cause of morbidity and death and is a high cost to health care systems. Screening currently offers the best chance of improving outcomes from bowel cancer. When introducing screening, the problems encountered in other cancers need to be avoided to maximize benefits and minimize harms.

Occult gastrointestinal bleeding

Occult gastrointestinal bleeding commonly manifests as iron deficiency anemia or fecal occult blood. Iron deficiency anemia results from chronic occult gastrointestinal bleeding. Evaluation of asymptomatic patients who have iron deficiency anemia or fecal occult blood usually should begin with investigation of the colon. Colonoscopy is preferred, but flexible sigmoidoscopy plus air contrast barium enema, or computed tomographic colonography may be acceptable in certain circumstances. If evaluation of the colon does not reveal a bleeding site, evaluation of the upper gastrointestinal tract is mandatory in patients who have iron deficiency anemia, and this should be considered in those who have fecal occult blood. In patients who have gastrointestinal symptoms, evaluation of the portion of the gastrointestinal tract from which the symptoms is derived should be pursued initially. The role of small intestinal investigation is controversial, and this probably should be reserved for patients who have iron deficiency anemia and persistent gastrointestinal symptoms or those who fail to respond to appropriate therapy. Celiac sprue should be considered as a potential cause of iron deficiency anemia in all patients. The treatment and prognosis of patients who have iron deficiency anemia or fecal occult blood depends on the gastrointestinal tract abnormality(ies) identified. Those without identifiable bleeding sites generally respond to conservative management and have a favorable prognosis. On the other hand, the outlook is poorer for patients with refractory occult blood loss or those who have vascular ectasias. Both groups of patients are clinically challenging and require a focused and experienced team approach to diagnosis and therapy.

Relative frequency of upper gastrointestinal and colonic lesions in patients with positive fecal occult-blood tests

BACKGROUND

Although bleeding lesions anywhere in the gastrointestinal tract can cause a positive reaction on guaiac-based fecal occult-blood tests, the relative frequency of upper gastrointestinal and colonic lesions is unknown.

METHODS

During a period of 30 months, we prospectively studied all patients with at least one stool specimen containing fecal occult blood who were referred for further evaluation. Fecal occult blood was detected by standard guaiac-based tests of stool specimens obtained as part of routine screening or of stool obtained by digital rectal examination. Patients with documented iron-deficiency anemia or active gastrointestinal bleeding were excluded from the study. All participants had a detailed history taken and underwent colonoscopy, followed by esophagogastroduodenoscopy.

RESULTS

Of the 409 patients with fecal occult blood who were referred, 310 were potentially eligible to participate, and 248 (mean age, 61 years; range, 40 to 89) were studied; 40 percent were women. We identified lesions consistent with occult bleeding in 119 patients (48 percent); in 71 bleeding lesions were found in the upper gastrointestinal tract, and in 54 they were identified in the colon. Six patients had abnormalities in both areas. The most common upper gastrointestinal lesions were esophagitis (23 patients), gastric ulcer (14), gastritis (12), and duodenal ulcer (10). Thirty patients with lesions in the upper gastrointestinal tract were long-term users of aspirin, ethanol, nonsteroidal antiinflammatory drugs, or a combination of these substances. The most common colonic lesions were adenomas more than 1.0 cm in diameter (29 patients), carcinoma (13), colitis (5), and vascular ectasia (5). Although the overall sensitivity of symptoms for the detection of gastrointestinal lesions was low, logistic-regression analysis demonstrated that the presence of symptoms in the upper gastrointestinal tract was associated with the detection of lesions in the upper gastrointestinal tract (odds ratio, 2.6; 95 percent confidence interval, 1.4 to 4.7). In both patients with symptoms and those without symptoms, the prevalence of lesions in the upper gastrointestinal tract was greater than or equal to that of colonic lesions.

CONCLUSIONS

In a group of patients with positive fecal occult-blood tests who were referred for further evaluation, from which those with iron-deficiency anemia and active bleeding had been excluded, upper gastrointestinal lesions were identified more frequently than colonic lesions.

Immunological determination of faecal haemoglobin concentrations in dogs

Faecal haemoglobin (Hb) concentrations in apparently healthy experimental Beagle dogs and in dogs of various breeds kept in private households or at breeders were measured by reversed passive latex agglutination (RPLA) and enzyme-linked immunosorbent assay (ELISA) in an effort to define the physiological concentrations of faecal Hb in the dog. In 88% (53) of 60 experimental Beagle dogs (30 males and 30 females), the RPLA titres were 1:2 and 1:8 and the faecal Hb concentrations ranged from 40.0 to 431.5 (mean 184.1 +/- 92.6) micrograms/g faeces by ELISA. No significant difference was found in Hb levels or RPLA titres between males and females. Seven dogs (12%) had significantly greater RPLA titres and Hb concentrations by ELISA than the remaining dogs. In 84% (45) of the 53 dogs kept in private households or at breeders, the RPLA titres were < 1:1 to 1:8 and the faecal Hb concentrations ranged from 7.1 to 456.7 (mean 137.5 +/- 128.7) micrograms/g faeces in ELISA. Eight of these dogs (15.1% of 53 dogs) had significantly greater RPLA titres and Hb concentrations by ELISA than the remaining dogs. There were no significant differences between the Beagles and dogs kept in private households or at breeders. In conclusion, in 98 (86.7% of 113) dogs the physiological concentrations of RPLA titres were < 1:1 to 1:8 and the faecal Hb concentrations were 143.5-185.1 micrograms/g (95% confidence level). Approximately 13.3% of apparently healthy dogs had higher faecal Hb concentrations, suggesting the presence of subclinical haemorrhages. Four dogs suffering from colorectal cancer also had high faecal Hb concentrations.

Evaluation of a fecal occult blood test with reverse passive hemagglutination for colorectal neoplasm screening

AIM: To evaluate the one and three sampling reverse passive hemagglutination fecal occult blood test (RPHA FOBT) for colorectal neoplasm screening.

METHODS: A group of 3034 individuals with histories of colorectal polyps and/or ulcers were screened for colorectal cancer. Three day fecal samples were collected and 60 cm fiberoptic colonoscopy was conducted for each subject. The fecal samples were tested for occult blood with the RPHA method and the endoscopic and histopathological diagnoses were used as standard reference for evaluation. The sensitivity, specificity and positive and negative predictive values of different samplings were compared.

RESULTS: About 521 cases of colorectal neoplasms were detected, including 12 cases of colorectal cancer and 509 cases of polyps. Results showed that the mean sensitivity of one sampling RPHA FOBT for colorectal neoplasm was only 13.2%, the specificity was 90.3% and the positive and negative predictive values were 21.3% and 83.4%, respectively; while for the three sampling, taking one positivity as positive, the sensitivity increased to 22.0%, the specificity decreased to 81.6% and the positive and negative predictive values were 19.7% and 83.6%, respectively.

CONCLUSION: A single RPHA FOBT seems to be less sensitive for screening for colorectal neoplasms. Since it is convenient and economical, RPHA FOBT remains the most practical procedure for detection of early colorectal cancer and polyps if it is combined with other screening methods.

Fecal alpha 1-antitrypsin detection of colorectal neoplasia. An evaluation using HemoQuant

Fecal alpha 1-antitrypsin measurement may be of value for the detection of colorectal neoplasia and is compared with the HemoQuant test in 119 subjects with either a screen-positive Hemoccult result (N = 78) or iron-deficiency anaemia (N = 41). Nineteen patients were found to have colorectal cancer, 35 had colorectal adenomatous polyps, 5 had inflammatory bowel disease, and 60 had no detected cause of occult blood loss. Of the cancer patients, 63% (12/19) were detected by fecal alpha 1-antitrypsin and 63% (12/19) by HemoQuant. Of the adenomas > 1 cm in diameter 33% (7/23) were detected by fecal alpha 1-antitrypsin and 26% (6/23) by HemoQuant. There was a poor correlation between fecal alpha 1-antitrypsin and HemoQuant results for colorectal cancers (r = 0.37, P > 0.05), and combining the tests, the sensitivity for colorectal cancer was increased to 84% (16/19). Fecal protein loss, as measured using alpha 1-antitrypsin, appears to involve largely different mechanisms from that of blood loss from colorectal cancers.

Population screening for colorectal cancer: comparison between guaiac and immunological faecal occult blood tests

There is concern about the low sensitivity of the guaiac-based Haemoccult test in mass population faecal occult blood (FOB) screening for the early detection of colorectal carcinoma. Hemeselect, an immunological FOB test, has been shown to be more sensitive for symptomatic colorectal cancer and may prove to be a more reliable screening method. In Brighton and Guildford, 4018 asymptomatic subjects aged 50-75 years were offered screening with Haemoccult and Hemeselect. A total of 1489 (37.7 per cent) completed both tests, of which 17 (1.1 per cent) were positive for Haemoccult and 145 (9.7 per cent) positive for Hemeselect (a total of 148 subjects had positive tests). Seven subjects (4.7 per cent) refused to be investigated. Colonic investigation in the remainder revealed nine cancers and 49 patients with 67 adenomas (32 tumours 1 cm or more in size). All cancers (Dukes A, six; B, one; C, two) were detected by Hemeselect (positive predictive value 6.2 per cent) but only one patient was Haemoccult positive (positive predictive value 5.9 per cent). Hemeselect detected 65 adenomas (31 of 1 cm or more) in 48 patients (positive predictive value 33.1 per cent) compared with 11 adenomas (seven of 1 cm or more) in eight patients who were positive for Haemoccult (positive predictive value 47.1 per cent). The test specificity for neoplasia was respectively 94.9 and 99.6 per cent. The Hemeselect positive rate is high but its substantial positive predictive value for cancer warrants continuing evaluation.

Detection of colorectal cancer by faecal alpha 1-antitrypsin

Alpha 1-antitrypsin was measured in 5-day faecal collections from patients with colorectal cancer or adenomatous polyps and a symptomatic control group. Collections were homogenized and lyophilized prior to measurement of alpha 1-antitrypsin by radial immuno-diffusion. Colorectal cancer dry weight concentrations were significantly higher than the symptomatic control results, with 57% having results greater than 95% normal values of this control group. There was no significant difference between adenomatous polyp dry weight concentrations and symptomatic control results. Wet weight concentrations were calculated from wet/dry ratios. Colorectal cancer wet weight concentrations were significantly higher than symptomatic control results with 48% having results greater than 95% normal values of this control group. Alpha 1-antitrypsin was also measured in non-lyophilized samples from an asymptomatic control group (n = 39). Colorectal cancer wet weight concentrations were significantly higher than asymptomatic control results, with 62% having results greater than 95% normal values of this control group. Faecal alpha 1-antitrypsin measurement deserves further assessment for use in detecting colorectal cancer.

Faecal occult blood testing in symptomatic patients: comparison of three tests

This study examines three faecal occult blood tests, Haemoccult, Fecatwin and E-Z Detect, each with different sensitivities, to determine which is best suited for use in symptomatic patients--both for the detection of cancer and of non-malignant mucosal disease of the large bowel. A test was completed by 1025 patients before double-contrast barium enema and the performance of each test was determined from the result of this investigation. The study was completed by 969 patients. There were 49 patients with colorectal cancer, 92 patients with a cancer or a polyp greater than 5 mm, and 130 with some mucosal abnormality. The test most sensitive for blood, Fecatwin, detected 14 of 15 (93 per cent) cancers and 29 (69 per cent) of 42 patients with mucosal disease (including inflammatory bowel disease) but gave three times as many false positive results as the Haemoccult test, which is less sensitive for blood. The chance of a patient with a positive Haemoccult result having mucosal disease on barium enema was 24 of 47 patients (51 per cent) (two-thirds of these having colorectal cancer). A negative Haemoccult result, however, was unreliable and should not influence patient management. A test less sensitive for blood than Haemoccult was found to be of little value in symptomatic patients.

Faecal occult blood screening for colorectal neoplasia: a randomized trial of three days or six days of tests

Haemoccult, a guaiac test for faecal occult blood, detects 56-78 per cent of asymptomatic carcinomas when performed over 3 days. In patients with known colorectal cancer the sensitivity of the test for neoplasia is increased by extending the test period to 6 days. We report the first randomized comparison of 3 day with 6 day testing in asymptomatic individuals. 35,184 age and sex matched individuals were randomly allocated to receive Haemoccult over 3 or 6 days. The tests were completed by 10,176 (57.8 per cent) of the 17,616 offered 3 day Haemoccult and 9461 (53.9 per cent) of the 17,568 offered 6 day Haemoccult, a significant decrease in compliance (P less than 0.001). Of the 3 day Haemoccult tests 131 (1.29 per cent) were positive, significantly fewer than the 160 (1.69 per cent) positive tests after 6 day Haemoccult (0.01 less than P less than 0.02). Investigation of subjects with a positive test revealed 20 carcinomas (1.14 per 1000 offered and 1.97 per 1000 completing the test) in the 3 day group and 24 carcinomas (1.37 per 1000 offered and 2.54 per 1000 completing the test) after 6 day Haemoccult tests (0.5 less than P less than 0.7 for those offered the test and 0.3 less than P less than 0.5 for those completing it). After 3 day Haemoccult 112 adenomas in 76 persons were detected (4.31 per 1000 offered and 7.47 per 1000 completing the test). In the 6 day group 123 adenomas in 83 persons (4.72 per 1000 offered and 8.77 per 1000 completing the test) were detected (0.5 less than P less than 0.7 for those offered the test and 0.3 less than P less than 0.5 for those completing it). Large adenomas were found in 27 individuals after 3 day testing (1.53 per 1000 offered the test and 2.65 per 1000 completing it) and in 35 individuals after 6 day testing (1.99 per 1000 offered the test and 3.70 per 1000 completing it) (0.3 less than P less than 0.5 for those offered the test and 0.1 less than P less than 0.2 for those completing it). This study has not demonstrated a significant increase in the yield of neoplasia in asymptomatic subjects offered Haemoccult over 6 days. However there was a significant decrease in compliance and a higher rate of colonscopy in those offered 6 day testing.

Haem in the gut. Part II. Faecal excretion of haem and haem-derived porphyrins and their detection

Only a fraction of haem (ferroprotoporphyrin) finding its way into the gut lumen is absorbed; the major portion enters the colon. There, unabsorbed haem, together with any haem of haemoproteins shed directly into the colonic lumen as haemoglobin or other haemoproteins, are converted by bacteria to a range of haem-derived porphyrins (HDP) lacking iron. This conversion is a slow and incomplete process and the amount converted in this way depends on colonic transit rate, site of bleeding and amount of luminal haem. As a consequence, faeces contain variable proportions of haem and HDP. The guaiac and tetramethylbenzidine tests give a qualitative index of faecal blood; they depend on the pseudoperoxidase activity of intact haem and cannot detect HDP. These tests perform better for large bowel bleeding than for more proximal bleeding. The fluorimetric HemoQuant assay quantitates both haem and HDP; it performs well for both proximal and distal bleeding. Neither type of test can allow for intestinal absorption of haem or HDP. Quantitation of gastrointestinal bleeding derived from measurement of faecally excreted haem and HDP is, therefore, likely to underestimate haem delivered into the gut lumen. In a given clinical situation, the choice of a haem-dependent occult blood test must take into account the possibility of colonic conversion of haem to HDP and the possible value of quantitation as opposed to qualitative detection.

Screening an asymptomatic population for colorectal cancer

The best prospect of realizing a reduction in mortality from colorectal cancer appears to be by presymptomatic detection in a screened population. Presently, the only feasible method of mass population screening is by the detection of faecal occult blood and it is encouraging that all the major trials demonstrate that asymptomatic malignancy may be detected in this way. Furthermore, the screen-detected cancers are generally at an earlier pathological stage than those appearing in control populations. However, a note of caution is required. At the present time it is too early to demonstrate a reduction in mortality from the disease and there is evidence of a length bias, with more of the screen-detected cancers being well differentiated. The results of the large controlled trials will enable the benefits of screening to be viewed objectively and a recommendation for, or against, screening to be made.

Patterns of occult bleeding in asymptomatic colorectal cancer

The assumption that asymptomatic colorectal cancers bleed provides the rationale for widespread stool screening. The authors studied 12 patients with unoperated colorectal cancer but without colorectal symptoms and six healthy volunteers as laboratory controls. All stools were collected for 2 weeks and analyzed by the HemoQuant and Hemoccult tests. In controls, the mean HemoQuant value was 0.7 mg hemoglobin (Hb)/g stool (range, 0.1-1.8) and all stools were Hemoccult-negative. In cancer patients, the mean HemoQuant was 3.3 mg Hb/g (range, 0.3-13.2); stools were within the normal HemoQuant range (less than 2 mg Hb/g) in 38% and negative by Hemoccult in 70%. The mean cancer detection rate testing a single stool per patient was 57% for HemoQuant and 25% for Hemoccult (P less than 0.001). The detection rate rose testing multiple stools and was maximal with five stools at 83% for HemoQuant compared to 31% for Hemoccult (P less than 0.001). The authors conclude that fecal blood levels are commonly normal with asymptomatic colorectal cancer. Although higher with HemoQuant than Hemoccult, cancer detection rates by fecal blood testing appear to be lower than previously reported.

Screening for colorectal cancer: a critical review

This article discusses the place of symptom detection, endoscopy, and fecal occult blood testing in population screening for colorectal cancer. There is now considerable evidence that screening the population over the age of 50 years for occult blood in the feces will result in an increased yield of tumors localized to the bowel at the time of surgical treatment. These tumors also have other favorable prognostic features and it is likely that the prognosis of this group will be better than the prognosis of patients presenting with symptoms in the usual way. Because of the biases that result from the selection and detection of tumors in screening studies, the mortality results of the control trials now underway must be awaited until it is known whether population screening is of real value. In chemical fecal occult blood screening tests, a compromise has to be made between sensitivity and specificity. The fecal occult blood test most widely used and the one that has been subjected to the most evaluation in screening studies is the guaiac-based slide test, Hemoccult. The predictive value of a positive test for invasive cancer is 11-17%, and for adenomas, 36-41%. This specificity is achieved at a loss of sensitivity, the interval cancer rate reported in screening studies being over 20%. Newly developed immunological techniques appear to be more sensitive and specific, but require further evaluation in population screening studies.

Sensitivity of Hemoccult test for large bowel cancer in high-risk subjects

From 1979 to 1982, 1233 symptom-free subjects at high risk for colon cancer because of family history and/or personal history of bowel neoplasia (cancer or adenomatous polyp) were examined with a guaiac test (Hemoccult II) for occult blood in stools. The test was positive (H+) in 98 subjects (7.9%). Endoscopy was subsequently performed on 86% of the H+ and on 64% of the H- subjects. Of 20 in invasive cancers found, 15 had been H+ [75.0%; 95% confidence interval (CI), 54.3-91.0%]. Of 96 patients with adenoma(s), 23 were H+ (24%; 95% CI, 16.0-33.0%). However, the sensitivity for adenomas was higher in patients with multiple adenomas or with a single adenoma measuring 2 cm or more in its largest diameter (37.5%; 95% CI, 21.8-54.7%). Of 699 subjects free of neoplastic lesions at endoscopy, 47 had been H+, ie, false positive (6.7%; 95% CI, 5.0-8.7%). Adjusting for differential compliance of H+ and H- subjects to endoscopy, a corrected estimate for sensitivity would be 69% for cancer and 19% for adenomas; the corrected estimate for the false-positive rate would be 5%.

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

Testing feces for occult blood is widely recommended as a means of detecting subclinical colorectal tumors. Guaiac tests such as Hemoccult are the most widely used, but chemical sensitivity is relatively low and the tests are affected by dietary peroxidases, the state of fecal hydration, and certain drugs. The newly devised HemoQuant and immunologic techniques appear more sensitive and specific, but they require further evaluation before widespread clinical usage can be recommended. Occult blood screening has both merits and weaknesses. Testing does uncover subclinical colorectal cancer, often at a relatively early stage, but whether this actually improves the prognosis remains to be proven. Benign neoplastic polyps are also detected, although it is debatable whether this is a valid rationale for screening. Test sensitivity for malignancy varies from good to moderate, but is poor for benign polyps. Specificity is usually around 97%-98%, yet the predictive value of a positive test for cancer is only about 10%; hence most test-positive individuals are needlessly subjected to invasive colonic investigations. Reported figures on public compliance with occult blood testing vary widely from excellent to poor. Published costs of screening are usually quite low, but these overlook important indirect and hidden expenses and are therefore misleading. On balance, the problems of occult blood testing currently appear to outweight the merits. This could change, however, with the newer testing techniques and with awaited mortality data from controlled clinical trials now underway.

Gastrointestinal blood loss associated with running a marathon

Gastrointestinal bleeding has been observed in long-distance runners. We prospectively studied participants of the Eighth Annual Marine Corps Marathon to determine the incidence of gastrointestinal blood loss associated with long-distance running. Of 600 runners contacted, 125 (21%) returned a questionnaire as well as pre- and postmarathon stool specimens. Stool specimens converted from Hemoccult negative to positive in 29/125 (23%) of the participants, indicating that running the marathon was associated with gastrointestinal blood loss (P less than 0.001). The incidence of this conversion (negative to positive) was significant for both males (N = 68, P less than 0.001) and females (N = 57, P less than 0.05). Gastrointestinal bleeding appeared to be independent of age, race time, abdominal symptoms, and the recent ingestion of aspirin, vitamin C, or steak.

Quantitative fecal recovery of ingested hemoglobin-heme in blood: comparisons by HemoQuant assay with ingested meat and fish

Blood, meat, or fish, or any combination thereof, were ingested by 9 normal volunteers to permit studies of the contained hemes during total gastrointestinal transit. Quantitative analysis of ingested heme and of fecal heme and its degradation products was made possible by a new specific and extremely sensitive test, HemoQuant. The average fecal recovery of hemoglobin-heme from 10 to 36 ml of blood was 88%, as determined in 13 separate studies. All Hemoccult tests remained negative despite greater than 20-fold increases in fecal heme. Up to 83% of the blood heme was converted in the intestinal tract to porphyrins. These porphyrins are included in the HemoQuant, but not in Hemoccult or other leukodye assays. Negligible amounts of heme were found in fish and fowl, and their ingestion led to no significant increase in fecal heme. An average of only 25% of the heme in ingested meat was subsequently recovered in feces. Control fecal values represented an average of approximately 0.5 ml of blood per day. The recovery data obtained show that fecal HemoQuant results reliably reflect the total amount of blood hemoglobin that enters the gastrointestinal tract.

Fecal blood levels in health and disease. A study using HemoQuant

We tested HemoQuant, a quantitative assay of fecal blood based on the fluorescence of heme-derived porphyrin, in 106 healthy volunteers, 170 patients with gastrointestinal symptoms but with normal diagnostic studies, 44 patients with gastrointestinal cancer, 75 patients with benign polyps, and 374 patients with a variety of other benign gastrointestinal lesions, including ulcers and erosions. In 98 per cent of the healthy volunteers, fecal hemoglobin concentrations were less than 2 mg per gram of stool. Levels were similarly low in stools from patients with symptoms and normal studies and in patients with relatively minor benign lesions. Within these groups, levels were slightly higher in those who had ingested red meat or aspirin. The fecal hemoglobin concentration was higher in patients with gastrointestinal cancer than in any other group, and 97 per cent of those with colorectal cancer had levels above 2 mg per gram. The sensitivity of HemoQuant was significantly greater than that of the guaiac test Hemoccult, particularly when heme was degraded or stools were dry. Intestinal degradation of heme to porphyrin can be measured separately by HemoQuant, and was greater when bleeding was from proximal lesions rather than distal ones. We conclude that HemoQuant is a more sensitive measure of gastrointestinal bleeding than Hemoccult, and that its capacity to measure degraded heme may be useful in indicating the anatomic site of bleeding.

Occult blood screening for colorectal carcinoma: a critical review

The author reviews the literature on occult blood surveillance for colorectal carcinoma. The guaiac-based Hemoccult (SmithKline Diagnostics, Sunnyvale, Calif.) test is the most reliable and widely used. However, testing is complicated by several technical issues that can affect clinical results, and even successful screening programs will miss a high proportion of tumors. Public compliance is often poor, and a number of indirect and "hidden" costs make surveillance programs much more expensive than is usually claimed. Almost all published screening trials are uncontrolled. They generally detect about 3-20 colorectal malignancies for every 10,000 people enrolled, but only about 5%-10% of occult blood reactions are due to cancer. Though screen-detected tumors tend to be at a relatively early stage, this does not imply any benefit of surveillance because of lead time and length biases inherent in the screening process. Only controlled trials can answer the central question of whether screening decreases mortality from bowel cancer. Two such trials are underway, but mortality data are not yet available from either.

Relative sensitivity of the fecal occult blood test and flexible sigmoidoscopy in detecting polyps

A group of 1,002 male pattern and model makers, an occupational group at high risk for colorectal cancers, was screened for the presence of polyps and malignancies of the lower gastrointestinal tract. Flexible sigmoidoscopy and serial fecal occult blood testing were both performed on 988 of the participants, and 165 were found to have at least one colorectal polyp. Only 3% of all men with visualized polyps showed Hemoccult-positive stools. Only 2 (4%) of the 51 men with histologically proven adenomatous polyps were Hemoccult positive. Adenomatous polyps of 1 cm or greater in diameter are malignant 8% of the time. This study concludes that the fecal occult blood test sensitivity in detecting colorectal polyps is unacceptably low. It should be supplemented by more rigorous procedures, especially in populations at high risk for colorectal cancer.

Five guaiac-based tests for occult blood in faeces compared in vitro and in vivo

Five guaiac-based faecal occult blood tests (Fecatest, Fecatwin Sensitive, Fecatwin, Haemoccult, Hemafecia) were compared in vitro and in vivo and the effect of time between sample application and development of the colour reaction was studied. In both type of experiments the sensitivity of Fecatest, Fecatwin Sensitive and Fecatwin was higher when the colour reaction was developed at 24-72 h than at 2 h after application of the sample but for Haemoccult and Hemafecia the sensitivity in in vivo experiments was constant or tended to decrease with time. In upper gastrointestinal bleeding false negative test results were obtained for Fecatest, Fecatwin Sensitive, Fecatwin, Haemoccult and Hemafecia in 21, 23, 38, 43 and 43%, respectively. In colorectal bleeding the corresponding percentages were 10, 10, 35, 35 and 35. Using the 51Cr-erythrocyte method, quantitative estimation of intestinal bleeding was performed in 20 patients with verified colorectal cancer and in 11 control patients. When the patient was bleeding from left hemicolon 29% of the Fecatwin, Haemoccult and Hemafecia test results were negative, 10% were negative for Fecatest and 14% for Fecatwin Sensitive. In patients with tumours in right hemicolon Fecatest and Fecatwin Sensitive were positive in all samples, whereas the other tests were negative in 10%. Experiments revealed that the proportion of false positives due to dietary factors correlated with the sensitivity of the tests.

Bleeding patterns in colorectal cancer: the effect of aspirin and the implications for faecal occult blood testing

Faecal occult blood testing for 3 consecutive days is recommended for the detection of colorectal cancer. Is this adequate? Haemoccult tests were performed for 6 days on the faeces of 50 patients with colorectal cancer. Enteric-coated aspirin was given during the final 3 days to see if its systemic effect on coagulation would increase tumour bleeding. In 25 patients blood loss was quantified by radiochromium assay. Bleeding was slight and intermittent with large daily fluctuations in individual patients. Median daily loss before aspirin was 1.2 ml and after aspirin 2.5 ml. Thirty per cent of the tumours were Haemoccult negative using the standard 3-day regimen and 18 per cent were negative after aspirin. Over the 6-day period, 10 per cent were persistently negative. We conclude that new methods are required to improve the diagnostic yield from faecal occult blood tests.

Evaluation for colon cancer in patients with occult fecal blood loss while taking aspirin: a Bayesian viewpoint

This paper examines the implications of occult fecal blood loss in patients taking aspirin (at least 2 grams daily). Although such patients do have a somewhat higher probability of colonic carcinoma than do members of the general population, their risk is far lower than that of patients who have gastrointestinal blood loss when not taking aspirin. This difference in risk exists because aspirin itself can provoke occult blood loss in stool. Patients who manifest gastrointestinal blood loss while taking aspirin can be separated into two groups, based on whether or not that blood loss continues after aspirin is discontinued. Although patients who continue to bleed are at high risk for colonic carcinoma, those who cease having any blood loss are at lower risk than are members of the general population. Further diagnostic studies to detect colonic carcinoma should be pursued in the former group, but not in the latter, low-risk group.

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.

Antiprostaglandin synthetase activity of nonsteroidal anti-inflammatory drugs and gastrointestinal micro-bleeding: a comparison of flurbiprofen with benoxaprofen

By using 51Cr-labelled erythrocytes and 141Ce-labelled microspheres to correct for daily variations in faecal output, gastrointestinal microbleeding was measured in hospital patients with rheumatoid arthritis before and after administration of 2 propionic acid derivatives. These were flurbiprofen and benoxaprofen, respectively a potent and a weak prostaglandin synthetase inhibitor. Increased faecal blood loss occurred consistently with flurbiprofen and not with benoxaprofen. Our results provide indirect evidence for the cytoprotective effect of prostaglandins on the gastrointestinal mucosa in man. The quantitative correlation between faecal occult blood loss as measured by the above techniques and the Haemoccult slide test is also discussed.

An immunofluorescent test for faecal occult blood

An immunological test for faecal occult blood is described, which is suitable for screening purposes. Fluorescein-labelled rabbit anti-human-haemoglobin serum is mixed with an aqueous faecal suspension, and free antibody is bound to a membrane sampler coated with human haemoglobin. The fluorescence on the membrane sampler is measured in a fluorometer, and the level of haemoglobin in the suspension is estimated. Advantages over chemical tests include absence of cross-reaction with animal haemoglobins, minimal observer error, and an adjustable sensitivity.

Occult faecal blood loss determined by chemical tests and a 51 Cr method

Stools from volunteers participating in an acetylsalicylic acid (ASA) study were examined during periods with restrictive and liberal diets. With 51Cr-determined faecal blood less than 2 ml/100 g, the rates of positive benzidine and 3,3' ,5,5'-tetramethylbenzidine (TMB) tests were about 5% and 25% for periods with restrictive and liberal diets, respectively. Similarly, Fecatest showed 2% positive tests on a restrictive and 8% on a liberal diet, whereas Hemoccult II slide and BM-test-Hemafecia showed less than 5% positive tests on both diets. When ASA-induced blood loss (mainly gastric) exceeded 5 ml/100 g faeces, the rate of positive benzidine and TMB tests, including the Hemo-Fec Test, varied from 87% to 100%. Fecatest detected half of these cases, whereas Hemoccult II and BM-test-Hemafecia were positive in less than one third. By repeated analyses of faecal specimens stored for 3 days, Fecatest showed a substantially increased sensitivity. We assume that benzidine and TMB tests are sensitive enough to detect occult blood loss from all levels of the gastrointestinal tract, but dietary restrictions are essential to reduce the rate of false-positive tests. Guaiac tests, perhaps with the exception of Fecatest, should be reserved for the detection of occult blood loss from the lower gastrointestinal tract.

False positive and negative hemoccult reactions on a normal diet and effect of diet restriction

The reliability of Hemoccult, a guaiac-impregnated slide for detecting faecal occult blood, was assessed on both normal and restricted diets. Two-hundred-and-twenty-five faecal samples were obtained from 40 patients on a normal diet, and 115 samples from 20 patients on a restricted diet. A single Hemoccult I test was performed on each sample. Faecal blood was quantitated by 51Cr red cell labelling. On a normal diet, the false positive rate was 11%. This reduced to 2% on a high fibre diet free of red meat and raw fruit and vegetables. This false positive rate is lower than has been previously reported for other, more widely-used, occult blood tests. The overall false negative rate was 48%; this diminished with increasing faecal blood loss.

Evaluation of radiochromium blood loss studies in unexplained iron-deficiency anaemia

Radiochromium measurement of gastrointestinal (GI) blood loss was performed on an outpatient basis on 57 patients with unexplained iron-deficiency anaemia. With the exception of pre-menopausal women, patients were only selected for study if the anaemia remained unexplained after careful GI radiological and endoscopic examination. Occult GI blood loss was confirmed in 31 patients and further investigation including laparotomy in some cases, led to a diagnosis in 17 of the 31. Carcinoma was present in five (colon four, stomach one) and benign lesions of the small intestine in five. There was no correlation between the severity or pattern of bleeding and the nature of the lesion. Of the 26 patients without demonstrable occult bleeding, anaemia was aspirin-induced in five and caused by menorrhagia in six. With the pre-menopausal women, measurement of both GI and menstrual blood loss resulted in detection of silent GI lesions in four and gynaecological disease in six. The cause of anaemia has not been elucidated in 23 of the 57 patients, including seven of 11 with aortic valve disease, even after follow-up for an average of 3.0 years. These results indicate that radiochromium studies effectively identify the patients with unexplained iron-deficiency anaemia who require continued active investigation for a focal GI lesion.

Feasibility of fecal occult-blood testing for detection of colorectal neoplasia: debits and credits

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.