Experience of adopting faecal immunochemical testing to meet the NICE colorectal cancer referral criteria for low-risk symptomatic primary care patients in Oxfordshire, UK

Abstract

ObjectiveTo compare the diagnostic performance of guaiac faecal occult blood (gFOB) testing with faecal immunochemical test (FIT) in a low-risk symptomatic primary care population to provide objective data on which to base local referral guidelines.DesignStool samples from routine primary care practice sent for faecal occult blood testing were analysed by a standard gFOB method and the HM-JACKarc FIT between January and March 2016. Symptoms described on the test request were recorded. Patients were followed up over 21 months for evidence of serious gastrointestinal pathology including colorectal adenocarcinoma.ResultsIn 238 patients, the sensitivity and specificity for colorectal adenocarcinoma detection using gFOB were 85.7% and 65.8%, respectively, compared with 85.7% and 89.2% for FIT. The positive predictive value (PPV) for gFOB was 7.1% and negative predictive value (NPV) was 99.3%. Comparatively, the PPV for FIT was 19.4% and NPV 99.5%. The improved performance of FIT over gFOB was due to a lower false positive rate (10.8 vs 34.2, p≤0.01) with no increase in the false negatives rate. For any significant colorectal disease, the PPV for FIT increased to 35.5% with a reduction in NPV to 95.7%.ConclusionIn this low-risk symptomatic patient group, the proportion of samples considered positive by FIT was considerably lower than gFOB with the same rate of colorectal adenocarcinoma detection. One in three of those with positive FIT had a significant colorectal disease. This supports National Institute of Health and Care Excellence recommendation that FIT can be reliably used as a triage test in primary care without overburdening endoscopy resources.

Faecal immunochemical testing for adults with symptoms of colorectal cancer attending English primary care: a retrospective cohort study of 14 487 consecutive test requests

“…The methodological approach used in the present study involved collection of faeces by the patient into a standard sample pot which was then sampled into the FIT collection device by trained staff in the laboratory. This approach was adopted due to local concerns that patients may incorrectly use the collection device: even sampling by laboratory staff shows high imprecision, 10,29 and patient collection into the device precludes concurrent testing for other faecal tests, such as calprotectin. It is possible that, as a consequence of the delay between collection and arrival in the laboratory, some degree of degradation may have occurred and the quantitative FIT value may represent an underestimation of the true haemoglobin concentration 30 .…”

“…Sample preparation prior to analysis on the FIT instrument utilized the Extel Hemo‐Auto MC device, a process which introduced additional variation, with overall analytical imprecision observed to be between 7.0% and 13.5% when specimens had been homogenised and sampled by laboratory staff. The selection of the faecal Hb concentration considered positive was made before the NICE recommendation to use 10 µg Hb/g faeces and was based on the methods lowest calibrant value of 7 µg Hb/g faeces and agreed with the OCCG based on initial method verification data 10 . Results were reported electronically to the requesting GP as either positive or negative.…”

“…FIT does not require dietary restriction, is specific to lower gastrointestinal (GI) cancers as upper GI enzymes degrade human globin, and is less affected by concomitant medication use than the guaiac method to detect faecal occult blood (gFOB) 7,9 . Accordingly, three times fewer false‐positive tests are reported when FIT is compared to gFOB in samples sent to the laboratory for symptomatic patients 10 . The adoption of FIT in primary care has been slow with notable variation in uptake and implementation across England, 5 low awareness of the NICE guidance 11 and low confidence in the accuracy of FIT amongst general practitioners (GPs) 12 .…”

Faecal immunochemical testing (FIT): Sources of analytical variation based on three years of routine testing in the context of DG30

“…FIT analysis was undertaken using the HM-JACKarc analyser (Kyowa Medex Co., Ltd., Tokyo, Japan) (ref Guildford report) which has a calibration range of 7 to 450 µg Hb/g faeces. This method was introduced into service prior to NICE guidance defining 10 µg/g as the threshold defined for detection and we used 7 µg/g, the lowest calibrator value as the threshold for a positive result All specimens were requested by NHS primary care clinicians and collected into standard stool pots by patients, a sampling approach taken due to concerns about sampling capability when undertaken by (often elderly) patients (5). Clinician advice from OUH and OCCG included guidance on delivering the sample to the laboratory on the same day as collection as Hb can degrade on storage (10).…”

Faecal immunochemical (rule-in) testing in general practice

“…but this has not led to the 'deluge' of referrals or worsening of the 'endoscopy capacity crisis' in the centres where FIT has been adopted. 3 The majority of the estimated 10% of consulting patients with abdominal complaints will not be referred for colonoscopy. 1 GPs conduct a careful triage using history and examination, an understanding of their patients' consulting patterns and comorbidity, preferences for testing, and by deciding when to respond to a positive result.…”