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Stability of external quality (EQ) samples for faecal occult blood - comparison of immunochromatografic and Guaiac tests

BACKGROUND-AIM: Immunochromatografic and guaiac-based faecal occult blood tests are used worldwide in population screening for colorectal cancer. Guaiac-based tests reveal hem component of hemoglobin whilst immunochromatografic tests reveal globin component of hemoglobin. Hem component is more stable than globin. However, immunochromatografic tests have higher sensitivity. The aim of this study was to examine EQ samples stability for faecal occult blood of both tests. METHODS: Three EQ samples (two liquid artificials S001 and S002 and a solid one S003) for faecal occult blood (immunochromatografic and guaiac- based tests) were examined every other day during 10 days. Samples were handled just as patients samples following the organizers and test instructions and analysis was done immediately after their arrival to the laboratory. Appearance of the blue color in guaiac test and pink line in immunochromatografic test field revealed positive result. RESULTS: Liquid artificials S001 and S003 were positive and a solid S002 was negative for faecal occult blood of both tests. Blue color in quaiac- based test as well as pink line in immunochromatografic test field was of the same intensity during the 10 days of examination for samples S001 and S003. CONCLUSIONS: External quality samples for faecal occult blood were stable after opening during 10 days of the examination and gave reliable results regardless of the used test. Although immunochromatografic test has better sensitivity it also has satisfying stability compared to guaiac test.

EQA ; stability ; fecal occult blood ; guaiac test

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