Effects of Fecal Sampling on Preanalytical and Analytical Phases in Quantitative Fecal Immunochemical Tests for Hemoglobin

Effect of multiple loading FIT sample collection devices on faecal haemoglobin concentration

BACKGROUND

Faecal immunochemical tests (FIT) are routinely used in colorectal cancer (CRC) screening programmes around the world. More recently, quantitative FIT has been recommended to help triage patients presenting to primary care with symptoms suggestive of CRC. Participants collect faecal samples using sampling probes which are inserted into sample collection devices (SCDs) containing preservative buffer. The SCDs have an internal collar designed to remove excess sample. The aim of this study was to investigate the impact of multiple loading on faecal haemoglobin concentration (f-Hb) using SCDs of four FIT systems.

METHODS

Pools of f-Hb negative samples were spiked with blood, homogenised and loaded into SCDs 1, 3 and 5 times, with insertion of the sampling probes into the SCDs with and without mixing between loads. The f-Hb was measured using the relevant FIT system. The percentage change in f-Hb for multiple loads was compared with a single load for each system for the mixed and unmixed groups.

RESULTS

The p values show a significant difference (p < 0.05) in the mass and f-Hb for the mixed and unmixed group, for 1-3 and 1-5 loads for all systems. The median percentage change in f-Hb for the mixed is higher than the unmixed group.

CONCLUSION

This study showed that multiple loading does significantly increase the f-Hb in the SCDs.

Faecal haemoglobin: Measurement, applications, and future potential

Faecal hemoglobin concentrations (f-Hb) can be quantitated using faecal immunochemical test for haemoglobin (FIT) analytical systems. FIT are of proven value and widely used in colorectal cancer (CRC) screening. Several factors affect f-Hb including sex, age, deprivation, geographical region, and FIT system. Thus, FIT data may not be transferable. Women are disadvantaged in programmes using a single f-Hb threshold for all participants, but risk scoring or sex stratified thresholds could be used to minimise this problem. In addition, low but detectable f-Hb, below the threshold, implies future risk of CRC. In several countries, where colonoscopy resources are constrained, FIT are now accepted as of added value in assessment of patients presenting in primary or secondary care with symptoms, although some serious colorectal disease is missed. Elevated f-Hb in the absence of any discernible colorectal lesions is common and has been found in several diseases with a systemic inflammatory component, including circulatory, respiratory, digestive, neuropsychological, blood and endocrine diseases, and others. There is growing evidence for the value of f-Hb in post-polypectomy surveillance, potentially saving costs and colonoscopy. There may be a role for FIT systems which have lower limits of detection than currently available methods. The faecal material remaining in FIT specimen collection devices could be used for further studies, including assessment of the microbiome. The estimation of f-Hb is now a mature investigative tool but further research will undoubtedly expand applications of value.

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.

A Quarter of Participants With Advanced Neoplasia Have Discordant Results From 2-Sample Fecal Immunochemical Tests for Colorectal Cancer Screening

BACKGROUND & AIMS

Some colorectal cancer (CRC) screening programs use 2-sample fecal immunochemical tests (FITs). We aimed to assess advanced neoplasia (AN) yield of 2 different FIT assays performed on the same bowel movement and have discordant results.

METHODS

We conducted a large prospective comparative accuracy study within the Dutch national CRC screening program to evaluate 2 quantitative FIT assays (FOB-Gold, Sentinel, Italy and OC-Sensor, Eiken, Japan) with comparable performance characteristics. We asked 42,179 screening-naïve individuals, 55-75 years old, to perform both tests on the same bowel movement, from May 2016 through March 2017. Participants with ≥1 positive test result (≥15 μg hemoglobin/gram feces) were invited for colonoscopy examination. Detection of AN by colonoscopy was the reference standard.

RESULTS

A total of 21,078 participants (50% participation rate) were included. FIT results were both negative for 19,032 participants (90%), both positive for 1163 participants (5.5%), and discordant for 883 participants (4.2%). AN was detected in 500 participants with 2 positive FIT results (43%) compared to 187 with discordant FIT results (21%) (p < .001). Of the 687 participants found to have AN by colonoscopy, 187 had only 1 positive FIT result (27%).

CONCLUSION

In a large 2-sample FIT-based CRC screening study, more than a quarter of participants in whom AN was detected by colonoscopy in the first screening round had discordant FIT results. AN was detected in one-fifth of those with FIT discordance. Participants with discordant results from 2 FITs should undergo colonoscopy. (www.trialregister.nl; no. NTR5874).

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.

Does the mass of sample loaded affect faecal haemoglobin concentration using the faecal immunochemical test?

Background

Quantitative faecal immunochemical tests (FIT) for haemoglobin are being used for colorectal cancer (CRC) screening for asymptomatic populations and are being indicated as a suitable test to rule out CRC in symptomatic populations. Faecal samples are typically collected by patients using a probe attached to the cap of a device which is inserted into a collection device into the preservative buffer, passing through a collar to remove excess sample: this process has potential for pre-analytical error. This study investigates whether faecal haemoglobin concentration (f-Hb) results are affected by the mass and method of sample collection.

Methods

Faecal samples with detectable f-Hb were loaded into collection devices from four manufacturers using increasing masses of sample. The f-Hb in the device buffer was measured using the relevant analyser. The results from the minimum recommended load were compared with results of ‘sample overloading’.

Results

The variation in the faecal mass added to the probe (overall CVs: EXTEL HEMO AUTO-MC Collection Picker 300%, OC-Auto Sampling Bottle 3 237%, SENTiFIT pierceTube 264%, Specimen Collection Container A 250%), was more than the variation in f-Hb (respective overall CVs: 62%, 35%, 47%, 39%). The mass of faeces added to the probes increased significantly ( P < 0.0001 for all four devices), but the f-Hb did not increase significantly (EXTEL HEMO AUTO-MC Collection Picker P = 0.6820, OC-Auto Sampling Bottle 3 P = 0.9368, SENTiFIT pierceTube P = 0.7551, Specimen Collection Container A P = 0.6864).

Conclusion

The mass of sample loaded onto the probe did not impact the f-Hb significantly using all four tested devices.