Chemical and immunological testing for faecel occult blood: a comparison of two tests in symptomatic patients

Abstract

Summary An established chemical faecal occult blood test (Haemoccult prepared without rehydration) has been compared with a new immunological test (Hemeselect) in patients referred for investigation of lower gastro-intestinal symptoms.Hemeselect was shown to have a higher sensitivity for colorectal carcinoma (94.0% compared with 58.0%), the greatest difference in sensitivity between the two tests being for rectal cancers. Similarly Hemeselect was more sensitive than Haemoccult for colorectal adenomas (66.6% vs 33.3%), and for inflammatory bowel disease (88.9% vs 33.3%).However the enhanced sensitivity of Hemeselect for colorectal neoplasia and inflammatory bowel disease was accompanied by a significant increase in the overall rate of positive reactions (32.8% of patients had a positive Hemeselect reaction compared with 14.8% who had a positive Haemoccult test), and a reduction in specificity (84.1% for Hemeselect vs 96.0% for Haemoccult).Hemeselect is a more sensitive indicator of colorectal neoplasia in symptomatic subjects, trials of its use as a screening test for asymptomatic neoplasia appear justified.Faecal occult blood tests are potentially useful in the preliminary assessment of subjects with symptoms of colorectal disease (Leicester et al., 1983) and also for mass population screening for asymptomatic colorectal neoplasia. The test commonly used for screening, Haemoccult (Rohm Pharma) has an estimated sensitivity in the range 50-65% for asymptomatic cancers (Kewenter et al., 1988;Kronborg et al., 1989;Hardcastle et al., 1989) and has been noted to be particularly insensitive for rectal and caecal cancers, missing over 50% of malignancies at these sites (Kronborg et al., 1989;Hardcastle et al., 1989). In contrast over 70% of sigmoid cancers are detected. One of the proposed mechanisms for this discrepancy is that Haemoccult, which is essentially a test for the Haematin moiety of Haemoglobin, relies on an optimum degree of Haemoglobin degradation which is most commonly achieved by blood loss from sigmoid cancers.Immunological tests, not dependent on Haematin, should reliably detect bleeding from rectal cancers, although they may also be affected by excessive degradation of blood from caecal cancers. Hemeselect (Smith-Kline Diagnostics) utilises fixed chicken erythrocytes that have coated with an antihuman haemoglobin antibody. Faecal matter is smeared onto filter paper by the patients. Small discs of the paper are then used to obtain a dilute faecal solution to which the coated chicken erythrocytes are added, erythrocyte agglutination occurs in the presence of haemoglobin in the faecal solution.The The sensitivity of both tests was independent of tumour stage (Table II).A total of 26 adenomatous polyps were diagnosed in 21 patients (Table III) Nine patients were shown to have an inflammatory condition affecting the colon or rectum (Table IV), of these three (33.39%) had a positive Haemoccult test and eight (88.9%) a positive Hemeselect test (Fisher's test, P = 0.02).The specificity for neoplasia or inf...

Comparison of a peanut agglutinin test and an immunochemical faecal occult blood test in detecting colorectal neoplasia in symptomatic patients

“…Their sensitivity for detecting colorectal neoplasia in asymptomatic patients with an average risk is fairly low, 50% -65% [2,3,20,21]. A detection rate of 45% -81% has been reported for symptomatic cancers [21]. Immunological tests, specific for human haemoglobin, have been shown to be more sensitive for symptomatic colorectal cancer than guaiac-based tests [21,22] and there is some evidence to show that they are more sensitive as a screening method for the asymptomatic population as well [20].…”

“…Guaiac tests based on the pseudoperoxidase activity of haemin are the most commonly used tests both in the preliminary assessment of subjects with symptoms of colorectal disease and in screening programs. Their sensitivity for detecting colorectal neoplasia in asymptomatic patients with an average risk is fairly low, 50% -65% [2,3,20,21]. A detection rate of 45% -81% has been reported for symptomatic cancers [21].…”

Effect of Verification Bias on the Sensitivity of Fecal Occult Blood Testing: a Meta-Analysis

“…The studies that evaluated the standard guaiac-based FOBT that did not correct for verification bias are listed in Table 1. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] In the last study, the data was presented in two separate publications. These 19 studies included 713 subjects with colorectal cancer and 4181 controls.…”

“…Both control-and cancersubjects underwent a confirmatory test, usually a colonoscopy though some of the older studies also utilized barium enema and sigmoidoscopy, particularly if FOBT negative. Most studies included subjects who submitted 3 stool specimens [31][32][33][34]36,37,39,41,44,[46][47][48][49][50] while some studies included subjects who only submitted one specimen 35,42,43 or the number was not specified. 38,40,45 Almost all of the studies reported that the specimens were collected at home while one study did not specify the location.…”

“…38,40,45 Almost all of the studies reported that the specimens were collected at home while one study did not specify the location. 38 The studies listed in Table 1 recruited subjects by two methods: inclusion of patients undergoing colonoscopy for a variety of indications (e.g., FOBT positivity, GI symptoms, colon cancer screening, polyp surveillance) [31][32][33][34][35][36][37][38][39]41,[44][45][46][47] or selection of a group of known colorectal cancer patients and controls undergoing colonoscopy. 40,42,43,[48][49][50] Both of these methods contain potential verification bias as not all of the FOBT negative patients in the population underwent a confirmatory test.…”