Faecal test as good as colonoscopy in detecting CRC

A faecal immunochemical test (FIT) is able to accurately rule out colorectal cancer (CRC) and is as sensitive as colonoscopy, the current gold standard for CRC diagnosis, the NICE* FIT study has shown.

FIT can thus be used for triaging patients for urgent investigations, with the potential to reduce the number of unnecessary colonoscopies.

“Our results show that FIT is essentially a very accurate home test for bowel cancer. If the test is negative in patients with symptoms, the chance of being cancer free is 99.8 percent,” said lead investigator Dr Nigel D'Souza from Croydon University Hospital, Croydon, UK.

“This test can be performed at home without needing to visit hospital or even your GP, which is particularly useful during this time of coronavirus,” he pointed out.

Excellent accuracy

To assess the diagnostic accuracy of FIT and utility in guiding referral for further investigation, the researchers conducted FIT in 9,822 patients with suspected CRC symptoms and compared these with findings from subsequent colonoscopy. Three cut-offs for FIT were assessed: 2, 10, and 150 µg/g. [Gut 2020;doi:10.1136/gutjnl-2020-321956]

At a cut-off value of 2 µg/g, FIT sensitivity was maximized to 97 percent  compared with 90.9 percent for 10 µg/g, which is the current recommended cut-off in NICE DG30 guidance.

In comparison, sensitivity of the gold standard colonoscopy has been shown to be 94.7 percent in a previous large meta-analysis of 9,223 patients. In this context, FIT sensitivity at a cut-off of 2 µg/g seems to be equivalent to colonoscopy in detecting CRC, according to the researchers.

Also, there was no significant difference in FIT sensitivity in subgroup analyses stratified by age, sex, ethnicity, deprivation, anaemia, and tumour characteristics, indicating that FIT can be applied for all symptomatic patients meeting the 2WW referral criteria.

“NICE have already recommended in their DG30 guidance use of FIT in primary care as a triaging tool for low risk symptoms before referral to secondary care; this strategy should be expanded to include all symptomatic patients,” suggested D’Souza and co-authors.

“The f-Hb*** cut-off for onwards referral should be set at the limit of detection of 2 μg/g to provide sensitivity equivalent to colonoscopy, the current gold standard for investigation and yet reduce referrals by 60 percent,” they added.

The corresponding negative predictive values (NPVs) were high, at 99.8 percent and 99.6 percent for 2 μg/g and 10 μg/g, respectively — which means patients with symptoms as per NICE criteria whose FIT result turned out negative had less than 0.5 percent chance of CRC.

“Importantly, a negative FIT result can be used to reassure patients that their symptoms are unlikely to be due to CRC because of the high NPV,” D’Souza and colleagues highlighted.

However, the very low risk (<0.5 percent false negativity) does not mean no risk, they pointed out. “In patients with undetectable f-Hb, 617 patients would need to undergo colonoscopy to detect one CRC; hence clinical acumen and safety-netting remains essential to identify patients with CRC and false negative FIT.”

With an area under the curve (AUC) of receiver operating characteristic (ROC) of 0.93, the researchers said this “confirms that the diagnostic accuracy of FIT is excellent, and on its own is at least as good as risk scores such as FAST (AUC 0.91) or COLONPREDICT (AUC 0.92).”

“At the lowest cut-off [of] 2 μg/g, a negative FIT result … can effectively rule out CRC and a positive FIT result is better than symptoms to select patients for urgent investigations,” concluded D’Souza and colleagues.

Many patients with bowel symptoms which meet the NICE 2WW** referral criteria for urgent investigation with colonoscopies will not have CRC — as symptoms for CRC are nonspecific, the researchers pointed out. However, the increasing number of referrals has quickly overwhelmed the capacity of endoscopy units in the UK.

“We would recommend incorporating FIT into referral pathway of symptomatic patients in primary care with appropriate safety netting, to reduce unnecessary referrals for investigations and help secondary care prioritize patients with higher risk of CRC,” urged the researchers.

“FIT will certainly revolutionize the way we manage patients with suspected bowel cancer symptoms,” said principal investigator Dr Muti Abulafi, also from Croydon University Hospital.