Analytical evaluation of four faecal immunochemistry tests for haemoglobin

Abstract

BackgroundFaecal immunochemical tests (FIT) for haemoglobin (Hb) are being used in the investigation of colorectal cancer. These tests use antibodies raised to the globin moiety of human Hb. Here, four automated quantitative FIT systems (HM-JACKarc, NS-Prime, OC-Sensor PLEDIA and SENTiFIT 270) are evaluated analytically to confirm whether the performance of the systems meet the manufacturers’ claims.MethodsAssessment of the analytical performance of the FIT systems was undertaken using Hb lysates, real patient samples and external quality assessment (EQA) samples. This analytical assessment focused on detection characteristics, imprecision, linearity, prozone effect, recovery and carryover.ResultsAll four methods demonstrated good analytical performance, with acceptable within- and between-run imprecision, good recovery of f-Hb and limited carryover of samples. They also all show good linearity across the range of concentrations tested. The results of EQA samples showed different variations from the target values (−52 to 45%), due to the absence of standardisation across the different methods.ConclusionsAll four systems are fit for purpose and have an analytical performance as documented by their manufacturers.

Assessment of the analytical performance of point-of-care faecal immunochemical tests for haemoglobin

“…Four laboratory-based quantitative assays have recently been evaluated and demonstrated to provide highquality analytical results. 2 f-Hb has been recommended for use in patients presenting with lower gastrointestinal symptoms that may be suggestive of colorectal cancer (CRC). 3 This has led to the increased use of FIT in primary care as a diagnostic tool for symptomatic patients.…”

Assuring the quality of examinations using faecal immunochemical tests for haemoglobin (FIT)

“…In addition to assessing transferability of IQC materials across FIT systems discussed above [8] and comparing the examination performance characteristics of four FIT systems [9], the research group have studied this aspect of the quality assurance of quantitative FIT. The rationale for the study was that, since EQAS are being established worldwide to support FIT examinations, the suitability of the materials currently provided by commercially available EQAS should be assessed [10].…”

“…For the study, EQAS organisers provided one or more materials with the following matrices: Hb spiked artificial faecal like matrix sent to participating laboratories for loading into FIT specimen collection devices, Hb spiked artificial faecal like matrix pre-loaded into FIT specimen collection devices by the EQAS organisers and then sent to participating laboratories, diluted Hb directly injected into the appropriate FIT system specimen collection devices by the EQAS organisers, Hb spiked liquid provided either lyophilised for reconstitution by the participating medical laboratory, or liquid ready to use after being portioned into system cups for direct sampling on the FIT system. The examinations were performed on the same four FIT systems used in the study of IQC materials [8] and previously evaluated [9]. The imprecision found on examination of samples with a faecal like matrix had a higher median CV (12.4-19.0%) when compared to those from samples with liquid matrices (0.8-2.3%).…”

“…There is an obvious limitation to this strategy in that the mean f-Hb found on examinations of each IQC material were different from those originally assigned by each manufacturer for their own FIT system. However, this is unsurprising given that there is currently no international standardisation or harmonisation of FIT, the methods are based on polyclonal antibodies, use different calibration techniques, are traceable to different primary reference materials and do not have identical examination performance characteristics [9]. Despite this, it was concluded that, if manufacturers were willing to market their IQC materials independently of their FIT systems, the potential exists for third party IQC materials for FIT to be widely available.…”

Faecal immunochemical tests in the COVID-19 pandemic; safety-netting of patients with symptoms and low faecal haemoglobin concentration – can a repeat test be used?

“…• should recommendations be developed regarding the most appropriate time interval that should elapse before a second FIT is requested: should this depend on symptom severity, • should more than one repeat FIT be done if symptoms persist beyond the finding of two low f-Hb, • if the repeat result is f-Hb 510 mg Hb/g faeces, should this be the criterion for referral for further investigation, or should a further repeat FIT be performed for confirmation of an increase in f-Hb, • should a threshold of <10 mg Hb/g faeces be applied as the criterion for reassurance, watching and waiting, or further safety-netting, since available FIT analytical systems have detectability characteristics 17 that are below this f-Hb, 18 allowing f-Hb to be detected at very low f-Hb and quantitated at lower f-Hb than this threshold: lower thresholds do increase diagnostic sensitivity for CRC, although positivity and colonoscopy demands do increase, 19 • should repeat or serial estimates of f-Hb in specimens from an individual patient be performed on one type of FIT system, since different systems give different numerical f-Hb results, especially at low f-Hb, 18 and • should professional bodies provide further best practice guidelines on how the sources of preanalytical, analytical and postanalytical variation can be minimized to ensure that any changes seen in an individual are due to important physiological or pathophysiological deterioration.…”