Faecal occult blood testing for population health screening May 2004

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Background Faecal occult blood testing Description of the technology and the procedure Faecal occult blood tests (FOBTs) are used to detect blood in faeces that is not obvious by general inspection (ie, occult blood). This technology has been utilised for both diagnostic and screening purposes; however, the purpose of this review is to investigate the relative performance of different FOBTs for population health screening. In general, FOBTs involve sample preparation prior to colorimetric visualisation. This may be conducted in the home, clinician’s office or a pathology laboratory. The most accepted regimen for faecal occult blood testing involves testing two faecal samples from each of three stools over three consecutive days. There are several alternative sampling methods associated with faecal occult blood testing. These include utilising either a wooden spatula or a brush, methods which involve a different degree of stool handling. The samples are then usually transferred onto a sample card which can be delivered by post to the appropriate location for development and interpretation. A single positive sample in the series is counted as a positive result. A high roughage diet is sometimes recommended prior to conducting the tests, in order to uncover lesions that bleed intermittently. FOBTs should not be conducted whilst the subject is experiencing menstrual or peri-anal bleeding. There are two types of FOBTs in common use: the long established guaiac tests and the newer immunochemical tests. Guaiac FOBTs The guaiac FOBTs act by detecting the intact haem molecule from haemoglobin. These tests are simple-to-perform colorimetric tests, often conducted in the home. Two small samples from stools obtained on three consecutive days are applied to a piece of paper impregnated with the guaiac gum. Upon application of a developing solution, the presence of trace amounts of haem results in a blue colour change due to the pseudoperoxidase actions of haem. Guaiac FOBTs are able to detect bleeding originating anywhere between the mouth and anus. However, the sensitivity of guaiac FOBTs for detecting upper gastrointestinal (GI) bleeding is less than for the lower GI tract. The accuracy of guaiac FOBTs can be affected by medications (eg, non steroidal antiinflammatory drugs (NSAIDs), anticoagulants, iron supplements), contamination of the sample with toilet water, time delay between sample collection and developing, and dietary factors (eg, haem in meat or peroxidases or catalases in many fresh fruits or vegetables or rare red meat). Since the tests are dependent upon the pseudo-peroxidase activity of haem, false negative tests will arise from excessive amounts of reducing agents in faecal samples (eg, vitamin C). Hydration of faecal samples is also known to increase test sensitivity with a loss of specificity. Delaying the development of the test for a few days after the collection of the sample minimises the effects of dietary peroxidases on test results; however, this may also diminish the chance of detecting a weak positive result. 2 Faecal occult blood testing
The guaiac FOBTs include brand names such as: Hemoccult, Hemoccult Sensa, Hemo FEC, Coloscreen, Fecatest (discontinued) and Shionogi B. Immunochemical FOBTs The immunochemical FOBTs involve the use of an anti-human monoclonal antibody, targeted at intact human blood-borne proteins (usually haemoglobin). These tests therefore have the theoretical advantage of not being affected by haem, peroxidases or anti-oxidases in the diet. In addition, immunochemical tests will not detect proximal bleeds, since in this case haemoglobin is digested before being passed in the faeces. However, these tests are generally more complex and expensive than the guaiac tests and often require laboratory processing. The immunochemical FOBTs include brand names such as: HemeSelect (discontinued) and Immudia-HemSp (international equivalents) (Young 1998), FlexSure OBT (discontinued), Magstream HemSp, Bayer Detect, Quicktest, DIMA FOB-10, !nSure, !nForm and BM-Test Colon Albumin. HemeSelect and Immudia-HemSp are reverse passive haemagglutination (RPHA) tests. These RPHA tests use chicken-erythrocytes coated with antibodies to human haemoglobin. The coated chicken-erythrocytes are agglutinated in the presence of haemoglobin in human faecal samples. HemeSelect, Immudia-HemSp, !nSure and FlexSure OBT utilise an anti-human monoclonal antibody to haemoglobin. BM-Test Colon Albumin utilises an antibody specific for human albumin. Two-tier tests There have been suggestions of using a “two-tier” approach to faecal occult blood testing, where a guaiac and then an immunochemical test are used in sequence for colorectal cancer (CRC) screening. This approach has been developed in response to the high positivity rates of some guaiac FOBTs. Following positive results from a highly sensitive guaiac test with an immunochemical test should increase specificity and reduce the associated high rates of unnecessary diagnostic follow-up. Studies using Hemoccult Sensa and HemeSelect in such a two-tier approach have been conducted (Allison et al 1996; Rae and Cleator 1994). Fecatwin Sensitive/Feca EIA was a combination of a guaiac and immunochemical test performed in two-tiers. Samples were initially screened with the Fecatwin Sensitive guaiac test and then positive samples were tested with the Feca EIA immunochemical test. This test is no longer commercially available. Intended purpose For diagnostic purposes, the use of both a guaiac and an immunochemical test together has been suggested, to differentiate between upper and lower GI tract bleeding. However, the purpose of this review is to investigate the relative effectiveness of different commercially available FOBTs when used for population health screening. The diagnostic use of FOBTs would need to be examined in a separate review. FOBTs are used as a screening test for the identification of CRC. This is based on the use of faecal occult blood as a marker for CRC. However, an inherent problem with the technology is that many other non-neoplastic disease processes can cause GI bleeding. Therefore, the sensitivity and specificity of a test for the detection of blood will not Faecal occult blood testing 3
Page 1 and 2: Faecal occult blood testing for pop
Page 3 and 4: Contents Executive summary.........
Page 5 and 6: Tables Table 1 Hierarchy of evidenc
Page 7: Figures Figure 1 Reasons for exclus
Page 10 and 11: BM-Test Colon Albumin. HemeSelect a
Page 12 and 13: The head-to-head studies examining
Page 14 and 15: sensitivity between tests contains
Page 17: Introduction The Medical Services A
Page 21 and 22: Classification of CRC may be by one
Page 23 and 24: Current reimbursement arrangement F
Page 25 and 26: Searches of the following secondary
Page 27 and 28: Identified by the search (n = 1214)
Page 29 and 30: Expert advice An advisory panel wit
Page 31 and 32: Trial Trial design Reviewed for eff
Page 33 and 34: eported (Robinson et al 1999). Of t
Page 35 and 36: unacceptable and unethical to subje
Page 37 and 38: Long-term follow-up Randomisation/
Page 39 and 40: Three different methods are used to
Page 41 and 42: • β j is a fixed effect which is
Page 43 and 44: Table 4 Meta-analyses of sensitivit
Page 45 and 46: Relative true positive rate and rel
Page 47 and 48: Table 7 Meta-analyses of relative F
Page 49 and 50: subject to verification bias due to
Page 51 and 52: The literature on FOBT screening fo
Page 53 and 54: Figure 3 Screening pathway used in
Page 55 and 56: Table 10 Prevalence used for indivi
Page 57 and 58: Table 15 and Table 16 outline the c
Page 59 and 60: Relevant sensitivity and specificit
Page 61 and 62: Table 22 Detection rates associated
Page 63 and 64: Following diagnosis of CRC, patient
Page 65 and 66: In the case of Hemoccult Sensa, col
Page 67 and 68: Of the two tests, Hemoccult Sensa d
Page 69 and 70:
Table 31 Life-expectancy from the b
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• The frequency of screening has
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Additionally, for both FOBTs, incre
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screening are higher, the differenc
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Conclusions Safety Faecal occult bl
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The incremental cost per life-year
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Summary of outcomes The Medical Ser
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Professor Bryant Stokes Neurologica
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Professor Graeme Young MBBS MD FRAC
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Specificity carcinoma Sensitivity c
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Appendix D Literature searches Medl
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Search history Results 26 hemeselec
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10. Bech K, Kronborg O, Fenger C (1
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33. Foliente RL, Wise GR, Collen MJ
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56. Hart AR, Barone TL, Gay SP, Ing
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79. Kronborg O, Fenger C, Olsen J,
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102. Lynch NM, McHutchison JG, Youn
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125. Nakama H, Fattah A, Zhang B, U
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148. Rasmussen M, Fenger C, Kronbor
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169. Scholefield JH, Moss S, Sufi F
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192. Walker AR, Whynes DK, Hardcast
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Appendix F Positive predictive valu
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Table 42 Meta-analyses of PPV for c
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Table 43 Meta-analyses of PPV for n
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Appendix G Diagnostic odds ratios A
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Figure 10 Summary receiver-operatin
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Appendix I Participation in FOBT sc
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Appendix J Relative cost-effectiven
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Number detected by screening or sym
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Appendix K Sensitivity analysis of
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Abbreviations AACR Australasian Ass
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References Aisawa T, Saito H, Kawag
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Hardcastle JD, Armitage NC, Chamber
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Rae AJ, Cleator IGM (1994), The two
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Young GP, St John DJB, Winawer SJ,
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Faecal occult blood testing for population health screening May 2004

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