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

Last edited 08/2023 and last reviewed 10/2023

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
    
    
• NICE have stated that (4):
  • Quantitative faecal immunochemical testing (FIT) using HM-JACKarc or OC-Sensor is recommended to guide referral for suspected colorectal cancer in adults
    • with an abdominal mass, or
    • with a change in bowel habit, or
    • with iron-deficiency anaemia, or
    • aged 40 and over with unexplained weight loss and abdominal pain, or
      
      
    • aged under 50 with rectal bleeding and either of the following unexplained symptoms:
      • abdominal pain
      • weight loss, or
        
        
    • aged 50 and over with any of the following unexplained symptoms:
      • rectal bleeding
      • abdominal pain
      • weight loss, or
        
        
    • aged 60 and over with anaemia even in the absence of iron deficiency
      
      
    • FIT should be offered even if the person has previously had a negative FIT result through the NHS bowel cancer screening programme. People with a rectal mass, an unexplained anal mass or unexplained anal ulceration do not need to be offered FIT before referral is considered
      
      
    • refer adults using a suspected cancer pathway referral (as outlined in NICE's guideline on suspected cancer) for colorectal cancer if they have a FIT result of at least 10 micrograms of haemoglobin per gram of faeces
      
      
    • for people who have not returned a faecal sample or who have a FIT result below 10 micrograms of haemoglobin per gram of faeces:
      • safety netting processes should be in place
      • referral to an appropriate secondary care pathway should not be delayed if there is strong clinical concern of cancer because of ongoing unexplained symptoms (for example, abdominal mass)
  
  
  
  • 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 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 (5) 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 (6) 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:

GP resources:

• PHE blog: New home test kit for bowel cancer screening: what GPs need to know
  
  
• CRUK - Introduction of the Faecal Immunochemical Test (FIT)

Reference:

1. Lee JK, Liles EG, Bent S, Levin TR, Corley DA. Accuracy of fecal immunochemical tests for colorectal cancer: systematic review and meta-analysis. Ann Intern Med. 2014;160:171
2. Allison JE, Fraser CG, Halloran SP, Young GP. Population screening for colorectal cancer means getting FIT: the past, present, and future of colorectal cancer screening using the fecal immunochemical test for hemoglobin (FIT) Gut Liver. 2014;8:117-130.
3. PHE Blog (August 2017). New home test kit for bowel cancer screening: what GPs need to know.
4. NICE (August 2023). Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care mary care
5. Mowat et al (2015). Faecal haemoglobin and faecal calprotectin as indicators of bowel disease in patients presenting to primary care with bowel symptoms. Gut Online First, published on August 20, 2015
6. Widlak MM et al. Diagnostic Accuracy of Faecal Biomarkers in Detecting Colorectal Cancer and Adenoma in Symptomatic Patients. Aliment Pharmacol Ther. 2017 Jan;45(2):354-363.