Image: The hema-Screen Specific kit for the rapid and qualitative determination of Occult Human Blood in fecal samples (Photo courtesy of Immunostics).
Screening with guaiac-based fecal occult blood tests (gFOBT), followed by colonoscopy for patients who test positive, has been associated with a reduction of 15% to 33% in colorectal cancer (CRC)–related mortality.
Fecal immunochemical test (FIT) methods have been developed. These immunoassays form an antibody antigen complex with the globin moiety of human hemoglobin (Hb) to generate either an immunoturbidimetric signal, which can be measured quantitatively or by lateral-flow immunochromatographic analysis, a qualitative band that can be detected visually.
A large team of scientists collaborating with those at Sunnybrook Research Institute (Toronto, ON, Canada) implemented a novel, standardized method to compare Hb stability across various fecal immunochemical tests. The stability of Hb was analyzed in collection devices inoculated with Hb-spiked feces and (1) stored at various temperatures (frozen, refrigerated, ambient, and elevated) for more than 60 days; (2) after undergoing three controlled, freeze-thaw cycles; and (3) after being transported by courier or postal services in uncontrolled temperature conditions from three locations in Ontario, Canada, to a central testing center. The team compared the stability of Hb across five different immunochemical kits and one guaiac kit.
The scientists found that the stability of Hb varied with time and temperature and by kit. Lower Hb recoveries occurred with increasing temperature and increasing time from sample collection to testing. Refrigeration provided the best stability, although results varied across kits, from 4.2 days to more than 60 days before a pre-specified threshold with less than 70% probability of the test results remaining positive was reached.
Freeze-thaw stability varied across kits and cycles. Hb recoveries from Hemoglobin NS-Plus, was 91.7% to 95.4%; while for OC-Sensor Diana, the Hb recovery was 57.6% to 74.9%. Agreement regarding Hb levels before and after transportation varied across kits, from 57% to 100%. The scientists found that the Hema-Screen SPECIFIC, was the best performer among the qualitative kits.
The authors concluded that important differences in Hb stability were found across the included fecal immunochemical tests and these findings should inform practice-based and population-based colorectal cancer screening. The study was published on October 2, 2017, in the journal Archives Of Pathology & Laboratory Medicine.
Sunnybrook Research Institute