faecal immunochemical tests (FIT) for hemoglobin and detection of bowel cancer

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Faecal immunochemical tests (FIT) for hemoglobin and detection of bowel cancer

Fecal immunochemical tests detect human globin by means of an antibody-based assay.

The FIT sampling technique is simpler and easier to collect compared to that of gFOBT

  • only one faecal sample is required and no dietary or medication restrictions are needed prior to the test
  • the test is specific for human haemoglobin - unlike the gFOBT
  • FIT is a quantitative test - the detection level for haemoglobin detected in a faecal sample is prespecified as to what defines a "positive" or "negative" test. In bowel cancer screening the levels used are significantly higher than if used in symptomatic patients

Efficacy of FIT in detection of colorectal cancer (CRC) over gFOBT (1,2)

  • overall accuracy of FIT for detection of CRC was 95% with 79% sensitivity and 94% specificity as been shown in systematic review and meta-analysis including 19 qualified studied performed by Lee et al
  • FIT has been shown to have a greater sensitivity in detecting advanced adenomas and CRC than guaiac-based fecal occult blood test (gFOBT)
  • FIT is also effective in detecting non-cancer significant bowel disease e.g. IBD

The use of FIT in the UK is proposed in three different settings - with different specified levels of haemoglobin in the faecal sample tested:

  • Bowel Cancer Screening
    • FIT is to be used in the bowel cancer screening programmes in the UK and will replace the use of gFOBT (3)
    • use of FIT instead of gFOBT will increase uptake to bowel screening by 6% because of "ease of use" and needing a single faecal sample versus six samples using gFOBT (3)
    • the level of Hb used for an abnormal versus a normal result has not yet been decided upon - however a level of greater than or equal 120 µg Hb/g faeces for defining an "abnormal result" will provide similar numbers of "positive" screening tests as occur at present
    • if a FIT test is positive ("abnormal result") then, in England and Wales, the bowel screening service will refer the patient for further investigation

  • FIT in symptomatic patients outside 2ww criteria
    • NICE criteria for requesting test for occult blood in faeces (FIT) (7)
      • offer testing with quantitative faecal immunochemical tests to assess for colorectal cancer in adults without rectal bleeding who:
        are aged 50 and over with unexplained:
        • changes in their bowel habit, or
        • iron-deficiency anaemia, or
      • are aged 60 and over and have anaemia even in the absence of iron deficiency

      • in the updated NICE symptom tables it states:
        • abdominal pain (unexplained) without rectal bleeding, and criteria for a suspected cancer pathway referral not met - offer testing with quantitative faecal immunochemical tests

        • change in bowel habit (unexplained) without rectal bleeding, and criteria for a suspected cancer pathway referral not met - Offer testing with quantitative faecal immunochemical tests

        • weight loss (unexplained) without rectal bleeding, and criteria for a suspected cancer pathway referral not met -Offer testing with quantitative faecal immunochemical tests

    • the the level of Hb used for an abnormal versus a normal result my vary with respect to implementation of this pathway
      • a level of greater than or equal to 10 µg Hb/g faeces for defining an "abnormal result" has been suggested by NICE (4)
    • an "abnormal test" meets the criteria for urgent cancer referral (3)

  • FIT as screening/triage of 2ww lower GI referrals
    • the use of FIT in this setting is not - at present - NICE approved
    • the concern is that various studies using FIT alongside 2ww lower GI referrals have not shown 100% sensitivity - ie some patients with a negative FIT test have been shown to have colorectal cancer
    • Mowat et al (6) used a FIT down to a level of a level of 10 µg Hb/g faeces and revealed a sensitivity of 89% in the equivalent of a 2ww population - ie 11 out of 100 patients with colorectal cancer had a negative FIT to a level of 10. The study did subsequently state a sensitivity of 100% by stating using FIT to test Hb to "detectable" levels but the paper did not define the methodology for this to be achieved - and so the 89% sensitivity based on a level of level of 10 µg Hb/g faeces is the only defined evidence in the study
    • Widlak el al (7) used a FIT down to a level of level of 7µg Hb/g faeces in patients referred under the criteria for 2ww lower GI - in this study there was a sensitivity of 84% - ie 16 out of 100 patients who were shown via colonoscopy etc to have colorectal cancer had a negative FIT at a level of 7
    • further studies are ongoing to ascertain the place and use of FIT in the 2ww lower GI referral pathway - currently this is the subject of extensive research being conducted in specific centres; and not recommended in routine practice

CRUK summary regarding FIT in bowel screening versus symptomatic:

Contributors:

  • Dr Lance Saker
    • GP Oak Lodge Medical Centre
    • Cancer Research UK Strategic GP
  • Dr Mark Welfare
    • Community gastroenterologist with Northumberland CCG and clinician with Northumbria Trust

GP resources:

Reference:

Last edited 09/2020 and last reviewed 11/2021

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