Colorectal malignancy (CRC) is one of the top three most common cancers in the UK but is considered to be very treatable due to recent improvements in early detection3. FIT testing was originally developed as an advancement on Faecal Occult Blood testing in bowel cancer screening. It is designed to detect small amounts of blood in faeces using monoclonal antibodies to the Hb molecule4. Recent evidence has found with some certainty that the use of quantitative faecal immunochemical testing has substantial benefits over the FOB test in both accuracy and compliance. This posed the question of whether FIT could be used as a primary diagnostic test rather than only for screening.
With rising awareness of CRC in the population, there has been an increase in the numbers of patients presenting to primary care with symptoms suggestive of CRC. This, coupled with a change in NICE guidance, resulted in more referrals to secondary care for 2WW cancer referrals and so in turn escalated the demand for colonoscopies.
If the current trend continues, Bowel Cancer UK estimates that there will be an increase in demand of 10–15% per year for diagnostic colonoscopies3. Endoscopy services are already stretched to capacity with the increasing demand and many patients breach the recommended 2WW for investigation. Secondly, endoscopic evaluation of the bowel is not without risk and carries a false negative rate of approximately 5%5. In addition, endoscopies are expensive and can be an unpleasant experience for patients.
In an attempt to streamline the referral system, initiatives have been created in some units such as nurse led colorectal telephone assessment pathways and the so called ‘straight to test’ pathway. These systems have been shown to reduce the time it takes for investigations to be carried out, but studies have revealed that patients may still be subject to inappropriate investigations for their symptoms, especially due to a lack of early assessment6. Thus, the identification of a cheaper, well tolerated investigation that has a robust sensitivity is of upmost importance. FIT has the potential to be used at the point of referral from primary care to guide the need for further investigations, reduce unnecessary colonoscopies and create a more cost-effective system. Despite this, it is important to consider the detection and removal of polyps during colonoscopy which reduces future CRC incidence and mortality.
When looking at Hb cut off values in faecal immunochemical testing, increasing the Hb cut-off decreases the sensitivity, decreases the specificity of the test and increases the number of false negatives. Using FIT with an Hb cut off of 4 µg Hb/g in our population, the number of false negatives would be 0.8. Although this is low, the acceptability of this rate on a larger scale must be considered. We forecast that any missed cancers would develop further symptoms and therefore represent at a later date. These theoretical patients with more advance disease have their own cost implications and more importantly the ethical implications associated with a missed cancer diagnosis. Robust safety netting advice for patients using FIT would be absolutely necessary.
Patients receiving negative FIT test results could be reassured they are unlikely to have cancer and discharged. Other possible outcomes of a negative FIT could be watch and wait, onward referral to colorectal outpatient clinic or repeat faecal immunochemical testing, particularly if the patient’s symptoms persist. It is vital that FIT results should not be viewed in isolation and clinical judgement remains of paramount importance. Results for high-risk polyps shows a reduced sensitivity/specificity and a higher false negative rate of 11 at the 4 µg Hb/g cut off and these would also have the possibility of missed malignancy.
Using a Hb cut-off of 4 µg Hb/g determined 258 false positives. This can be explained as FIT detects haemoglobin associated with a variety of other pathology such as inflammatory bowel disease or high-risk polyps. Data from other studies suggested that up to 28.9% of patients with an initial false positive result from a FIT were eventually diagnosed with some form of serious bowel disease. In our forecast, the patient who received a positive result would undergo colonoscopy as per the protocol and therefore patient disruption would be minimal.
Overall, the results of this study are positive and reveal a highly sensitive and specific test that could be used as a primary investigation for 2WW patients to facilitate the saving of colonoscopy resources. The cost of endoscopy to NHS England in 2014 was approximately £178.4 million and it was found that approximately 40% of tests were normal8 which is comparable to our study. This study shows the cost of diagnosing colorectal cancer and high-risk polyps via endoscopy is significantly higher than the forecasted cost of FIT at £27,459 and £24,618 vs £15,554 and £13,945 respectively. This is a potential cost reduction of 43% over 2 years (£309,521).