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.