Prescreening evaluation of a brush-based faecal immunochemical test for haemoglobin.

OBJECTIVES: To undertake a prescreening evaluation of a new brush-based faecal immunochemical test for haemoglobin, relative to a traditional spatula-sampling immunochemical test. SETTING: Patients aged between 24 and 90 years, scheduled to undergo diagnostic colonoscopy in two major urban hospitals, for a range of clinical indications. DESIGN: Patients sampled three stools using a spatula for the reference FlexSure OBT test and two stools using a brush for the InSure test; order of sampling was randomised. Faecal haemoglobin was quantified by a modified InSure in a subset of patients to determine whether brush-sampling allowed discrimination between groups. MAIN OUTCOME MEASURES: Sensitivity for cancer or adenoma; false-positive rate in normals. Faecal haemoglobin levels. Preference for sampling method. RESULTS: InSure and FlexSure OBT did not differ in their sensitivities for cancer (27/36, 75% vs 29/36, 80.5%, respectively), adenomas >or= 10 mm (12/29, 41.4% vs 13/29, 44.8%) or adenomas <10 mm (each 8/56, 14.3%). Likewise, false-positive rates in normals were similar: 4/179 (2.2%) and 5/179 (2.8%) respectively (specificities of 97.8% and 97.2%, respectively). Levels of faecal haemoglobin were highest in those with cancers; those with adenomas had intermediate levels which were also significantly higher than those in normals. The brush sampling method was preferred by 38/46 (82.6%), while 4/46 (8.7%) preferred the spatula (p<0.00001). CONCLUSIONS: InSure is as sensitive and specific as FlexSure OBT for faecal haemoglobin. The novel stool-sampling method of InSure allows discrimination between normals and classes of neoplasia, and is highly preferred. The brush-sampling faecal immunochemical test InSure should now be evaluated in a screening population.

Interference of plant peroxidases with guaiac-based fecal occult blood tests is avoidable.

Peroxidase-rich fruits and vegetables are reputed to interfere with guaiac-based fecal occult blood tests. We added horseradish peroxidase to fecal samples and tested them with Hemoccult, Hemoccult SENSA(R), and hydrated Hemoccult. Positivity rates with Hemoccult and Hemoccult SENSA decreased rapidly as the time between smearing (preparation) and development increased, whereas they remained high with hydrated Hemoccult. For samples with added blood, positivity rates did not decrease with time. When 61 volunteers were tested on a standard restriction and on a challenge diet high in plant peroxidase, no positive results occurred during standard restriction. During the challenge diet, one volunteer was positive with Hemoccult and Hemoccult SENSA when development was delayed 24 h, and no volunteers were positive when it was delayed 48 h and 72 h. However, with hydrated Hemoccult, positives occurred in 13 of 61 volunteers at 24 h, 8 of 61 at 48 h, and 5 of 61 at 72 h. Thus, peroxidase-rich plant foods do not need to be excluded from the diet with Hemoccult and Hemoccult SENSA if development is delayed for at least 48 h after smearing. A delay of this duration will not solve the problem of plant peroxidase interference with hydrated Hemoccult.

A study of laboratory based faecal occult blood testing in Melbourne, Australia. The Faecal Occult Blood Testing Study Group.

Faecal occult blood tests (FOBT) are widely used in clinical practice and are under increasing scrutiny as a tool for colorectal cancer screening. However, there is little information regarding the quality of testing performed in pathology laboratories. Therefore, we asked 13 pathology laboratories in Melbourne, Australia, to test coded contrived faecal samples prepared from a composite stool specimen which had been spiked to various concentrations of haemoglobin. The samples were provided to the laboratories in two forms: (i) on/in the sample collection device appropriate for the faecal occult blood test they normally used; and (ii) as a moist faecal sample. Some variation in threshold analytical sensitivity between laboratories for the same FOBT was observed for Hemoccult SENSA, ColoRectal, Hematest, MonoHaem and Hemolex suggesting that, at least for those tests, technician training could be improved. Two tests, Hematest and an in-house FOBT did not perform as well as the other FOBT. When samples were sent in moist form, Hemoccult SENSA (P = 0.0002), ColoRectal (P = 0.02) and MonoHaem (P = 0.04) had significantly lower overall positivity rates; for Hemolex the decrease was not significant (P = 0.3). The lower positivity rate with moist samples is important, given that 11 of the 13 laboratories in the study stated that they receive at least some samples in moist form. Thus, technician training and laboratory procedure need to be reviewed to maximize the benefits of faecal occult blood testing in clinical practice, especially with its expanding role in colorectal cancer screening.

A new approach to fecal occult blood testing based on the detection of haptoglobin.

BACKGROUND: Colorectal carcinoma is a common disease, occurring in 1 in 20 adults in Western society, and there is a compelling need for an effective early diagnostic test. Several serum tests, including carcinoembryonic antigen have been used, but none are sufficiently sensitive for the early diagnosis of the disease. METHODS: In a novel approach using fecal extracts from patients with colorectal cancer as the antigen for immunization, several MoAbs were produced. One (FE14.1) was found to react with the feces from patients with colon cancer, but not with those from normal subjects. A sandwich enzyme-linked immunoadsorbent assay was developed, and its ability to diagnose colorectal carcinoma evaluated. RESULTS: Of the patients with colorectal carcinoma, 91.5% (43/46) were positive compared with 1.9% of normal individuals (4/211). Analysis of the N-terminal amino acid sequence of a subunit of the molecule detected by FE14.1 shows it to be the beta chain of haptoglobin. CONCLUSIONS: The assay developed in this study has several advantages compared with current fecal occult blood tests, including no requirement for dietary restriction and the ability to distinguish between upper and lower gastrointestinal bleeding, while retaining the sensitivity and specificity of the current tests. Furthermore, the sensitivity of the tests increases to 100% if the FE14.1 and HemeSelect are combined. In addition, the study shows the potential to produce anticancer agents by immunizing with fecal material.