FIT sample stability for haemoglobin-positive faeces using three analytical systems over seven days


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Carolyn Piggott1,Cerin John1,Helen Bruce1
1NHS Bowel Cancer Screening Programme Southern Hub

Abstract

Background

Automated quantitative faecal immunochemical test (FIT) for haemoglobin (Hb) systems include a faecal sampling device (with preservative buffer), laboratory analyser and reagent. In colorectal cancer screening programmes samples are usually collected at home and posted for laboratory testing. We investigated the change in Hb concentration over seven days using naturally Hb-positive faeces and three FIT systems.

Method

Twenty two Hb-positive samples were taken from stools provided for calprotectin analysis and mixed for two minutes using wooden sticks. Two FIT sampling devices for each of the FIT systems Extel Hemo Auto-MC Collection Picker (Kyowa Medex Co. Ltd.), SENTiFIT pierceTube (Sentinel Diagnostics), and OC-SENSOR Autosampling Bottle 3 (Eiken Chemical Co. Ltd.) were loaded with each of the 22 samples. After mixing and incubation for 24 hours at room temperature, Hb was measured using the HM-JACKarc, SENTiFIT 270 and OC‑SENSOR PLEDIA analysers, respectively. All sampling devices were stored in the dark at 19oC (15-23oC) for seven days. After mixing the samples, Hb was re-measured on day 7. The average percentage difference between the Hb concentration on day 1 and day 7 was calculated.

Results

For the Extel Hemo /HM-JACKarc system the average percentage difference from day 1 to day 7 was ‑11.6%, the minimum percentage difference was ‑36.5% and the maximum 4.3%; for the SENTiFIT pierceTube/SENTiFIT 270 system the average percentage difference was 2.1%, the minimum percentage difference was ‑35.4% and the maximum 18.7%; for the OC-SENSOR /PLEDIA system the average percentage difference was ‑1.1%, the minimum percentage difference was ‑19.4% and the maximum 24.9%.

Conclusion

The average percentage difference of the Hb concentration was negative over seven days for the Extel Hemo /HM-JACKarc and the OC-SENSOR /PLEDIA systems, and positive for the FOB Gold/SENTiFIT 270 system. The preservative buffer in each of the three manufacturers’ devices is likely to vary, which could explain these differences.