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

Abstract

words)Aims: To determine analytical capabilities of a commonly used faecal immunochemical test (FIT) to detect haemoglobin (Hb) in the context of NICE guidance DG30, and the likely use of FIT to reprioritise patients delayed by the COVID-19 pandemic.Methods: Data obtained from independent verification studies and clinical testing of the HM-JACKarc FIT method in routine primary care practice were analysed to derive analytical performance characteristics.Results: Detection capabilities for the FIT method were 0.5 µg/g (limit of blank), 1.1 (limit of detection) and 15.0 µg/g (limit of quantification). 31 of 33 (94%) non-homogenised specimens analysed in triplicate were consistently categorised relative to 10 µg/g compared to all 33 (100%) homogenised specimens. Imprecision in non-homogenised specimens was higher (median 27.8%, (range 20.5% -48.6%)) than in homogenised specimens (10.

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

“…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 . The excellent discriminatory value of FIT (AUC of 0.941) and the low number of false negatives reported in this large in‐context cohort indicates that haemoglobin degradation is not a major limitation of clinical performance when using a low threshold of FIT 29 …”

“…Specimen preparation is a critical step in the overall performance of the FIT method 28,29 . 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.…”

“…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 .…”

Diagnostic accuracy of Faecal Immunochemical Testing for patients with symptoms of colorectal cancer: a retrospective cohort study of 14,487 consecutive test requests from English primary care

“…Specimen preparation is a critical step in the overall performance of the FIT method (18,19). The methodological approach used in the present study involved collection of stool by the patient into a standard stool sample pot which was then sampled into the FIT method collection device by trained staff in the laboratory.…”

Letter: extending FIT from DG30 to NG12 patients. Letter: faecal immunochemical testing for adults with symptoms of colorectal cancer – ready for prime time? Authors' reply: a unified approach to safety netting negative FITs is required

“…Our laboratory staff sampled 33 faecal specimens in triplicate. 8 About 31 (93.9%) specimens were consistently positive or negative around ≥10 µg Hb/g. The variability of FIT results (median coefficient of variation, 27.8%, range 20.5% to 48.6%) was reduced after specimens were homogenised (10.2%, 7.0% to 13.5%), and all specimens were consistently categorised.…”