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Effect of delay in sampling on haemoglobin determined by faecal immunochemical tests
Louise F Brown1, Callum G Fraser
1Department of Biochemical Medicine, Ninewells Hospital and Medical School, UK. l.brown3@nhs.net
Annals of Clinical Biochemistry
|September 11, 2008
Summary
Delaying stool sampling for faecal immunochemical tests (FIT) significantly reduces haemoglobin concentrations, leading to false-negative results. Always use FIT collection devices for fresh faeces to ensure accurate cancer screening.
Area of Science:
- Clinical Chemistry
- Gastroenterology
- Oncology
Background:
- Traditional faecal occult blood tests (FOBT) require direct sampling onto cards due to haemoglobin degradation in containers.
- Faecal immunochemical tests (FIT) are replacing FOBT, but traditional collection methods may persist.
- The impact of delayed stool sampling on FIT accuracy remains a concern.
Purpose of the Study:
- To evaluate the effect of delayed stool sampling on the accuracy of faecal immunochemical tests (FIT).
Main Methods:
- Faecal samples from healthy volunteers were spiked with haemolysate to achieve FIT-positive concentrations.
- Samples were analyzed daily for 1-14 days using quantitative FIT.
- Qualitative FIT was performed after 5 and 10-day delays.
Main Results:
- Haemoglobin concentrations decreased daily, with rates proportional to initial concentrations.
- After 8 days, all samples had <100 ng/mL; after 9 days, all had <50 ng/mL.
- Qualitative FIT results became negative after delays, with 5/15 initially positive samples turning negative after 5 days and 0/15 positive after 10 days.
Conclusions:
- Delayed sampling of fresh faeces into or onto FIT devices can cause false-negative results.
- Laboratories analyzing faeces from traditional containers risk missing significant neoplasia.
- Direct sampling using FIT collection devices is crucial for accurate faecal occult blood testing.
