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

Last edited 09/2020 and last reviewed 04/2023

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:

Related pages:

faecal occult blood testing (summary section)

NICE - quantitative faecal immunochemical tests (FIT) to guide referral for colorectal cancer in primary care

faecal calprotectin or FIT (faecal immunochemical test)

FIT as screening or triage of 2ww lower GI referrals