Moisture content of Hemoccult slides influences test sensitivity

The guaiac-based fecal occult blood test in healthy dogs: Evaluation of the effects of diet, and the ability of the test to detect fecal occult blood

BACKGROUND

The guaiac-based fecal occult blood test (gFOBt) has been used for human colorectal cancer screening. It can detect the fecal occult blood (FOB) in dogs after oral administration of 20 mg of hemoglobin/kg body weight of blood and is influenced by diet.

OBJECTIVES

The aims were to evaluate the effect of diet and the ability of gFOBt to detect FOB in healthy dogs after oral administration of autologous blood.

METHODS

Five healthy dogs were fed Purina Hypoallergenic (HA) and Gastrointestinal (EN) diets. Feces were tested with gFOBt before starting diets and at each defecation (hereafter referred to as fecal collection event) throughout the study period. Every 4 days, increased doses of autologous blood were administered orally. The whole blood of one dog was progressively diluted with a saline solution, and dilutions were directly tested with the gFOBt, until a negative result was found.

RESULTS

Twelve of 185 (6.5%) gFOBt were found to be positive. No associations between diet and gFOBt positivity were found. A significant association was found between the fecal collection event and gFOBt positivity (P < .001) and between doses of blood and gFOBt positivity (P = .048). The lowest dilution ensuring all positive tests was 6.5 µg_Hgb /mL.

CONCLUSIONS

The gFOBt was not influenced by either the HA or EN diets. The gFOBt positivity was associated with the dose of blood and the fecal collection event. However, caution is needed in the interpretation of results due to the lack of an association between gFOBt positivity and increasing doses of blood in the same dog.

Faecal occult blood testing for colorectal cancer screening: the past or the future

Screening for colorectal cancer (CRC) reduces CRC mortality; many countries have implemented population-based CRC screening programmes and many more are poised to do so. Whilst several different CRC screening modalities are available, choice will be influenced by cost, available resources (e.g. high-quality colonoscopy) and acceptability of the test by the invited population. For CRC screening, no screening test has so far surpassed the practicality, affordability and effectiveness of tests for the presence of blood in faeces (faecal occult blood tests, FOBt). The results of several large FOBt-based randomised controlled trials provide the best clinical evidence to support their use in population-based CRC screening. This review considers the current options for CRC screening and the future for FOBt.

Advances in Fecal Occult Blood Tests: the FIT revolution

There is a wide choice of fecal occult blood tests (FOBTs) for colorectal cancer screening.

GOAL

To highlight the issues applicable when choosing a FOBT, in particular which FOBT is best suited to the range of screening scenarios. Four scenarios characterize the constraints and expectations of screening programs: (1) limited colonoscopy resource with a need to constrain test positivity rate; (2) a priority for maximum colorectal neoplasia detection with little need to constrain colonoscopy workload; (3) an "adequate" endoscopy resource that allows balancing the benefits of detection with the burden of service provision; and (4) a need to maximize participation in screening. Guaiac-based FOBTs (gFOBTs) have significant deficiencies, and fecal immunochemical tests (FITs) for hemoglobin have emerged as better tests. gFOBTs are not sensitive to small bleeds, specificity can be affected by diet or drugs, participant acceptance can be low, laboratory quality control opportunities are limited, and they have a fixed hemoglobin concentration cutoff determining positivity. FITs are analytically more specific, capable of quantitation and hence provide flexibility to adjust cutoff concentration for positivity and the balance between sensitivity and specificity. FITs are clinically more sensitive for cancers and advanced adenomas, and because they are easier to use, acceptance rates are high.

CONCLUSIONS

FOBT must be chosen carefully to meet the needs of the applicable screening scenario. Quantitative FIT can be adjusted to suit Scenarios 1, 2 and 3, and for each, they are the test of choice. FITs are superior to gFOBT for Scenario 4 and gFOBT is only suitable for Scenario 1.

Tests and investigations for colorectal cancer screening

Worldwide, colorectal (CRC) is the third most common form of cancer, after lung and breast cancer, and the fourth most common cause of cancer death, although in developed countries CRC incidence is higher and it accounts for an even higher proportion of cancer deaths. Successful treatment of early-stage CRC confers substantial survival advantage, and there is now overwhelming evidence that screening average-risk individuals for CRC reduces the incidence and disease-specific mortality. In spite of considerable research for new biomarkers for CRC, the detection of blood in faeces remains the most effective screening tool. The best evidence to date for population-based CRC screening comes from randomised-controlled trials that used a guaiac-based faecal occult blood test (gFOBt) as the first-line screening modality, whereby test-positive individuals are referred for follow-up investigations, usually colonoscopy. A major innovation in the last ten years or so has been the development of other more analytically sensitive and specific screening techniques for blood in faeces. The faecal immunochemical test for haemoglobin (FIT) confers substantial benefits over gFOBt in terms of analytical sensitivity, specificity and practicality and FIT are now recommended for CRC screening by the European guidelines for quality assurance in colorectal cancer screening and diagnosis. The challenge internationally is to develop high quality CRC screening programmes for which uptake is high. This is especially important for developing countries witnessing an increase in the incidence of CRC as populations adopt more westernised lifestyles. This review describes the tests available for CRC screening and how they are being used worldwide. The reader will gain an understanding of developments in CRC screening and issues that arise in choosing the most appropriate screening test (or tests) for organised population-based screening internationally and optimising the performance of the chosen test (or tests). Whilst a wide range of literature has been cited, this is not a systematic review. The authors provide FOBT CRC screening for a population of 14.6 million in the south of England and the senior author (SPH) was the lead author of the European guidelines for quality assurance in colorectal cancer screening and diagnosis and leads the World Endoscopy Organization Colorectal Cancer Committee's Expert Working Group on 'FIT for Screening'.

Effect of season and ambient temperature on outcome of guaiac-based faecal occult blood tests performed for colorectal cancer screening

AIM

Guaiac-based faecal occult blood tests (gFOBTs) are used in the colorectal cancer screening programme. Recent data suggested that the immunological faecal occult blood test illustrated a variation in positivity according to season and ambient temperature. Our aim was to assess the effect of season and ambient temperature on the positivity rates of the gFOBT during pilot screening for colorectal cancer.

METHOD

Data from the first year of round 1 of the pilot screening programme in Coventry and Warwickshire were analysed. Patients with positive and negative gFOBT samples were included. Patients with spoilt samples or incomplete data were excluded. Of the total of 59513 patients, 30311 were men and 29202 women. Mean age was 56 years. Daily temperature data were provided by the meteorological office.

RESULTS

Median exposure of the gFOBT test card was 6 days (range 1-17). Median daily maximum temperature was 14°C. Spring and summer illustrated significantly decreased positivity rates compared with autumn and winter (Pearson's chi-squared test, P<0.001). Mean daily maximum temperature for the test card exposure showed no significant difference in positivity rates (P=0.53). Subgroup analysis revealed a significant reduction in positive samples in the >25°C subgroup (P=0.045).

CONCLUSIONS

There is a seasonal variation in positivity rates of gFOBTs with increased positivity in spring and summer months. There is no difference in positivity rates in relation to ambient temperature except in subgroup analysis where there is a significant reduction in positivity rates above 25°C.

Colorectal cancer screening: why immunochemical faecal occult blood test performs as well with either one or two samples

BACKGROUND

Immunochemical faecal occult blood tests perform as well with either one or two samples, and better than guaiac tests with 6 samples.

AIMS

Clarifying relationship between tests' performance, bleeding pattern and observation level.

METHODS

The data of 32,225 average-risk subjects who performed both Hemoccult II (guaiac) and Magstream (immunochemical) tests were re-analysed by varying the cutoff and number of samples of Magstream.

RESULTS

The identical performances obtained using one or two samples of Magstream (lower cutoff for one sample) at the population level were explained by opposite patterns of bleeding according to the presence of advanced neoplasias. They translated into discrepancy at the individual level: for example a 60% increase in sensitivity and 20% in specificity observed with one (39ng Hb/ml cutoff) or two samples (63ng Hb/ml cutoff) Magstream compared with Hemoccult II meant that 28.5% of the subjects testing positive with one sample (18.0% in subjects with advanced neoplasias) would have been considered negative by using two samples of Magstream at a higher cutoff (and reciprocal).

CONCLUSION

The identical performance of immunochemical tests using one or two samples (different cutoff), explained by opposite pattern of bleeding according to advanced neoplasias is true only at the population level, the appropriate level for mass screening.

Performance improvements of stool-based screening tests

Stool testing is a widely accepted, non-invasive, technique for colorectal cancer (CRC) screening. Guaiac-based faecal occult blood test (gFOBT) screening has been proven to decrease CRC-related mortality; however gFOBT is hampered by a low sensitivity. Faecal immunochemical tests (FITs) have several advantages over gFOBT. First of all, FIT has a better sensitivity and higher uptake. Furthermore, the quantitative variant of the FIT allows choices on cut-off level for test-positivity according to colonoscopy resources available, personal risk profile, and/or intended detection rate in the screened population. Stool-based DNA (sDNA) tests aiming at the detection of specific DNA alterations may improve detection of CRC and adenomas compared to gFOBT screening, but large-scale population based studies are lacking. This review focuses on factors influencing test performance of those three stool based screening tests.

Diagnosis of colorectal cancer by faecal calprotectin: an analysis of 87 cases

AIM: To explore the values of faecal calpro-tectin, faecal occult blood tests and serum carcinoembryonic antigen (CEA) in the diagnosis of colorectal cancer.

METHODS: Faecal calprotectin, faecal occult blood and serum CEA were detected in 60 healthy adults and 87 patients with colorectal cancer. Tumor location and Dukes' stages were obtained from postoperative pathological examination.

RESULTS: The sensitivities of faecal calprotectin, faecal occult blood test and serum CEA were 88.51%, 83.91% and 44.83%, respectively, in the diagnosis of colorectal cancer, while the specificities were 88.33, 96.67% and 93.33, respectively. The positive rates of faecal occult blood test and serum CEA in patients with Dukes' stage C and D were significantly higher than those in patients with Dukes' stage A and B (P = 0.0173, 0.0059). There was no significant difference in faecal calprotectin level in patients with different tumor locations and Dukes' stages. Faecal calprotectin in combination with FOBT and/or CEA demonstrated a little higher sensitivity.

CONCLUSION: Faecal calprotectin is sensitive in the diagnosis of colorectal cancer, and can be used as a non-invasive surrogate marker for screening colorectal cancer in outpatients.