TO F.O.B OR NOT TO F.O.B…. THAT IS THE QUESTION by Dr Ishani Patel
The use of FOBT (guaiac method) has been recommended in the NICE guidelines NG12 Suspected cancer: recognition and referral published in June earlier this year.
Offer testing for occult blood in faeces to assess for colorectal cancer in adults without rectal bleeding who:
- are aged 50 and over with unexplained abdominal pain or weight loss, or
- are aged under 60 with: – 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.
Refer people using a suspected cancer pathway referral (for an appointment within 2 weeks) for colorectal cancer if they are aged over 60 and occult blood in their faeces.
The concerns raised include:
- Guidelines does not specify which FOBT
- Guaiac FOBT is the only FOBT available and only in few hospital labs
- Guaiac FOBT uses a complex algorithm requiring 9 stool samples – Dedicated labs with staff performing large numbers – Strict quality assurance
- It is positive in up to 50% of colorectal cancers in asymptomatic patients
- Less than 2% are designated positive which means 98% will be reassured
- There is a 50% chance of being correct if negative
- The gold standard remains colonoscopy or CT colonography
The profession expressed reservation in a letter to the BMJ in July 2015 stating the following:
“…. the recommendation to use FOBT could lead to patients being referred for a poor quality test and could lengthen the time to receiving a definitive diagnosis. The guideline suggests that a standard qualitative guaiac FOBt could be used to determine the cause of symptoms. This is potentially dangerous, as the test misses around 50% of cancers, in a screening setting at least, compared to a 95 per cent detection rate for colonoscopy. The false-negativity rate quoted in the evidence statement is very high for symptomatic patients and could give patients and GPs false reassurance. Furthermore, no cut-off for faecal haemoglobin concentration has been specified nor type of test. It is likely that current research will point the way to using quantitative immunochemical testing for faecal blood (FIT) in symptomatic patients and internationally we are seeing this test replace the standard guaiac FOBt in screening settings but until then the evidence for FOBt in symptomatic patients is poor.“
Professor Willie Hamilton, NICE guidelines Development Group responded with the following:
“….half of patients with colorectal cancer did not meet the criteria for urgent referral under CG27, the previous guidance. These patients generally had low-risk-but-not-no-risk symptoms. They did badly, with longer times to diagnosis, a higher proportion of emergency admissions, and higher mortality. The 2015 guidance sought to improve this. Firstly, the new guidance brought some symptom groups not in the 2005 guidance into the urgent group, as their symptom profile exceeded the chosen threshold of a 3% risk of cancer. This led to concern from some surgical groups, who believed the additional workload may be unsustainable. In the context of delayed diagnosis in many people with colorectal cancer, the guideline development group (GDG) believed that it was important to revise the threshold in this way; making it consistent with other cancers. The literature review on testing in suspected colorectal cancer identified six research papers on the use of faecal occult blood testing (FOBt) in the symptomatic primary care population. Overall, these supported the use of FOBts. A rigorous economic analysis addressed the several different testing options available for this low-risk group (including colonoscopy and no testing) and found FOBts to be markedly the most cost-effective. So colonoscopy was inferior from a cost-effectiveness viewpoint. It would also have been impractical to extend colonoscopy to this large low-risk population. Surgeons were already concerned at our recommendations for additional referrals (and thus colonoscopies) – if we had recommended colonoscopy for the low-risk group too, there was a real danger that the NHS colonoscopy service would have been unable to cope. The letter focusses on concerns re false-negatives – which we specifically addressed in a recommendation in the guidance. We need to think of the true positives. FOBts have five supportive studies in symptomatic patients in primary care: faecal immunochemical tests (FITs) have none. The one study of FITs in that population concluded that their diagnostic accuracy was insufficient. It may be that FITs will prove superior to FOBs once more studies have been performed. The wording of the recommendation does not specify which test is to be used – it simply recommends that occult blood in faeces is sought for. Should FITs prove superior at a later date, then a change to FITs can be made. We deliberately future-proofed the recommendation. Until research in the symptomatic population shows FITs to be superior (it may not, of course), FOBts provide an evidence-based, cost-effective, test which can be used on a group of patients previously ill-served by NHS cancer diagnostics. This will save lives – NICE’s intention throughout."
Across the country cancer services and CCGs are debating whether to support the use of FOBT and working collaboratively to develop straight-to-test pathways for symptomatic patients over 40 who do not meet the new criteria.
So when you next locum be mindful to check whether the local Trust even offers FOBT and cross-check with local endoscopy pathways!