Faecal immunochemical test for patients with 'high-risk' bowel symptoms: a large prospective cohort study and updated literature review

Background

We evaluated whether faecal immunochemical testing (FIT) can rule out colorectal cancer (CRC) among patients presenting with ‘high-risk’ symptoms requiring definitive investigation.

Methods

Three thousand five hundred and ninety-six symptomatic patients referred to the standard urgent CRC pathway were recruited in a multi-centre observational study. They completed FIT in addition to standard investigations. CRC miss rate (percentage of CRC cases with low quantitative faecal haemoglobin [f-Hb] measurement) and specificity (percentage of patients without cancer with low f-Hb) were calculated. We also provided an updated literature review.

Results

Ninety patients had CRC. At f-Hb < 10 µg/g, the miss rate was 16.7% (specificity 80.1%). At f-Hb < 4 µg/g, the miss rate was 12.2% (specificity 73%), which became 3.3% if low FIT plus the absence of anaemia and abdominal pain were considered (specificity 51%). Within meta-analyses of 9 UK studies, the pooled miss rate was 7.2% (specificity 74%) for f-Hb < 4 µg/g.

Discussion

FIT alone as a triage tool would miss an estimated 1 in 8 cases in our study (1 in 14 from meta-analysis), while many people without CRC could avoid investigations. FIT can focus secondary care diagnostic capacity on patients most at risk of CRC, but more work on safety netting is required before incorporating FIT triage into the urgent diagnostic pathway.

The Fast Track FIT study: diagnostic accuracy of faecal immunochemical test for haemoglobin in patients with suspected colorectal cancer

BACKGROUND

The faecal immunochemical test (FIT) is now available to support clinicians in the assessment of patients at low risk of colorectal cancer (CRC) and within the bowel cancer screening programme.

AIM

To determine the diagnostic accuracy of FIT for CRC and clinically significant disease in patients referred as they were judged by their GP to fulfil National Institute for Health and Care Excellence guideline 12 (NG12) criteria for suspected CRC.

DESIGN AND SETTING

Patients referred from primary care with suspected CRC, meeting NG12 criteria, to 12 secondary care providers in Yorkshire and Humber were asked to complete a FIT before investigation.

METHOD

The diagnostic accuracy of FIT based on final diagnosis was evaluated using receiver operating characteristics analysis. This permitted a statistically optimal cut-off value for FIT to be determined based on the maximisation of sensitivity and specificity. Clinicians and patients were blinded to the FIT results.

RESULTS

In total, 5040 patients were fully evaluated and CRC was detected in 151 (3.0%). An optimal cut-off value of 19 µg Hb/g faeces for CRC was determined, giving a sensitivity of 85.4% (95% confidence interval [CI] = 78.8% to 90.6%) and specificity of 85.2% (95% CI = 84.1% to 86.2%). The negative predictive value at this cut-off value was 99.5% (95% CI = 99.2% to 99.7%) and the positive predictive value 15.1% (95% CI = 12.8% to 17.7%). Sensitivity and specificity of FIT for CRC and significant premalignant polyps at this cut-off value were 62.9% (95% CI = 57.5% to 68.0%) and 86.4% (95% CI = 85.4% to 87.4%), respectively; and when including all organic enteric disease were 35.7% (95% CI = 32.9% to 38.5%) and 88.6% (95% CI = 87.5% to 89.6%), respectively.

CONCLUSION

FIT used in patients fulfilling NG12 criteria should allow for a more personalised CRC risk assessment. FIT should permit effective, patient-centred decision-making to inform the need for, type, and timing of further investigation.

Faecal immunochemical tests for haemoglobin: Analytical challenges and potential solutions

Quantitative faecal immunochemical tests for haemoglobin (FIT) are being used increasingly around the world in colorectal cancer screening programmes, and in patients presenting with lower bowel symptoms to determine who should proceed to further bowel visualisation investigations, usually colonoscopy. The clinical utility of FIT is well reported. There are a number of analytical challenges including pre-analytical variation, difficulty setting up external quality assessment schemes, access to third party internal quality control material and a lack of standardisation or harmonisation of FIT methods. Here we report the work of the International Federation of Clinical Chemistry FIT Working Group. We provide an overview of the main pre-analytical variables; discuss different approaches to external quality assurance of FIT; propose a solution to third party internal quality assurance materials and summarise the challenges of standardisation and harmonisation of FIT.

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

BACKGROUND

Faecal immunochemical testing (FIT) is recommended by the National Institute for Health and Care Excellence (NICE) to triage symptomatic primary care patients for further investigation of colorectal cancer.

AIM

To ascertain the diagnostic performance of FIT in symptomatic adult primary care patients.

METHODS

Faecal samples from routine primary care practice in Oxfordshire, UK were analysed using the HM-JACKarc FIT method between March 2017 and March 2020. Clinical details were recorded. Patients were followed for up to 36 months in linked hospital records for evidence of benign and serious (colorectal cancer, high-risk adenomas and bowel inflammation) colorectal disease. The diagnostic accuracy of FIT is reported by gender, age group and FIT threshold.

RESULTS

In 9896 adult patients with at least 6-month follow-up, a FIT result ≥10 µg Hb/g faeces had a sensitivity for colorectal cancer of 90.5% (95% CI 84.9%-96.1%), specificity 91.3% (90.8%-91.9%), positive predictive value (PPV) 10.1% (8.15%-12.0%) and negative predictive value (NPV) 99.9% (99.8%-100.0%). The PPV and specificity for serious colorectal disease were higher and the sensitivity and NPV lower than for colorectal cancer alone. The area under the curve for all adults did not change substantially by gender or by increasing the minimum age of testing. Using ≥10 µg Hb/g faeces, 10% of adults would be investigated to detect 91% of cancers, a number needed to scope of ten to detect one cancer. Using ≥7, ≥50 and ≥150 µg Hb/g faeces, 11%, 4% and 3% of adults would be investigated, and 91%, 74% and 54% cancers detected, respectively.

CONCLUSION

A FIT threshold of ≥10 µg Hb/g faeces would be appropriate to triage adult patients presenting to primary care with symptoms of serious colorectal disease. FIT may be used to reprioritise patients referred with colorectal cancer symptoms whose investigations have been delayed by the COVID-19 pandemic.

An evaluation of ten external quality assurance scheme (EQAS) materials for the faecal immunochemical test (FIT) for haemoglobin

Objectives

External quality assessment schemes (EQAS) are being established worldwide to support the faecal immunochemical test (FIT) for haemoglobin (Hb). FIT is widely used as a screening test for colorectal cancer and increasingly in assessment of patients presenting with symptoms. EQA for FIT is provided in several matrices, each unique to the individual scheme. These include Hb suspended in a faecal-like matrix, lyophilised samples and liquid samples. The aim of this study was to evaluate commercially available EQAS and assess their suitability for use.

Methods

Ten EQAS provided material for the study. EQA samples were analysed on four quantitative FIT systems. 15 faecal-like matrix samples were loaded per concentration per FIT system. Reconstituted lyophilised samples were examined five times on three separate occasions and liquid samples were examined 10 times per concentration per FIT system. The coefficient of variation (CV) was calculated per concentration of EQA for each FIT system.

Results

Results from faecal-like matrix schemes had a higher median CV (12.4-19.0%) when compared to those from schemes providing liquid matrices (0.8-2.3%). The spread of CV values was also higher for results from faecal-like matrix schemes with an interquartile range (IQR) 4.4-24.0% vs. liquid IQR range of 0.3-2.5%.

Conclusions

Hb results from faecal-like matrices, whilst more aligned to a patient or participant sample, are prone to pre-examination variation so do not assess the analytical accuracy of a FIT system. Liquid matrices are not prone to pre-examination variation and are better able to assess the accuracy of a FIT system.

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

OBJECTIVE

To 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.

DESIGN

Stool 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.

RESULTS

In 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%.

CONCLUSION

In 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.

Diagnostic accuracy of one or two faecal haemoglobin and calprotectin measurements in patients with suspected colorectal cancer

BACKGROUND

The role of faecal biomarkers in patients at 'high risk' of colorectal cancer (CRC) is not yet defined. Pre-analytical factors, such as heterogeneity of biomarker distribution within faeces, may influence their optimisation in clinical practice. We undertook to determine whether repeat or combined biomarker testing improves diagnostic accuracy for CRC or clinically significant disease.

METHODS

Patients referred with suspected CRC provided two separate faecal samples each for faecal immunochemical testing (FIT) and faecal calprotectin (FC) prior to investigation. Diagnostic accuracy of FIT and FC were evaluated based on final diagnoses.

RESULTS

Five hundred fifteen patients completed a full colorectal evaluation. The optimal cut-off for CRC using a single FIT was ≥12 µgHb/g faeces (84.6% sensitivity, 88.5% specificity). For two FIT, the cut-off was ≥43 µgHb/g faeces if either and ≥2 µgHb/g faeces if both were positive. There was no advantage in their diagnostic accuracy compared with a single FIT. FC had a lower diagnostic accuracy for CRC than FIT, which was not improved by repeat FC. No benefit was identified with FIT-FC combined. For CRC, significant adenomatous polyps and organic enteric disease combined, FIT and FC performed similarly to each other but were poorer predictors (AUC 0.677 and 0.660). There was no uplift in diagnostic accuracy when the tests were repeated or combined.

CONCLUSION

This study supports using a single FIT at a cut-off close to that recommended by NICE DG30 to improve diagnostic accuracy for 'two-week wait' patients referred with suspected CRC.

Setting up a service for a faecal immunochemical test for haemoglobin (FIT): a review of considerations, challenges and constraints

Quantitative faecal immunochemical tests for haemoglobin (FIT) have now been advocated by the National Institute for Care and Health Excellence (NICE: DG30) to assist in the triage of patients presenting with symptoms that suggest a low risk of colorectal (bowel) cancer. The evidence is that FIT provides a good rule out test for significant bowel disease. However, a small number of cases will be missed, and robust safety-netting procedures are required to follow up some FIT-negative patients. A range of diagnostic pathways are possible, and there is no best approach at present. Introduction of FIT requires careful consideration of the logistics of supply of devices and information to requesting sites and of transport to the laboratory. A number of FIT analytical systems are available. Three are documented as appropriate for use in assessment of patients with symptoms. However, preanalytical, analytical and postanalytical challenges remain. The methods have different specimen collection devices. The methods use polyclonal antibodies and there is no primary reference material or method to which FIT methods are standardised. Third-party internal quality control is lacking, and external quality assessment schemes have many difficulties in providing appropriate materials. Reporting of results should be done using µg Hb/g faeces units and with knowledge of the limit of detection and limit of quantitation of the analytical system used. FIT can be used successfully in an agreed diagnostic pathway, along with other clinical and laboratory information: this requires a multidisciplinary approach, providing opportunities for professionals in laboratory medicine involvement.