Fecal Immunochemical Test for Hemoglobin Evaluated on Automated System

Most of the new CRC cases are found in patients presenting with symptoms in primary health care, such as changes in bowel habit and red blood in the feces.

Fecal immunochemical tests (FIT) for detection and quantification of detection of hemoglobin in feces (f-Hb) are well established and have replaced traditional guaiac-based tests in national screening programmes in most European countries. Several quantitative immunochemical tests are available, however only a few tests are available on high throughput automated analyzers.

Medical Biochemists and their colleagues at the Aalesund Hospital (Aalesund, Norway) evaluated, as part of a study, 163 symptomatic patients over 18 years referred to colonoscopy for assessment of lower abdominal symptoms. The study was performed between January 2020 and February 2021. Invitation to colonoscopy together with a collection device and detailed instructions for sampling of feces was sent by mail 2-4 weeks before meeting for colonoscopy. Patients were asked to collect a fecal sample 3-7 days before colonoscopy. There were no dietary restrictions before sampling.

Fecal samples were collected in FOB Gold sample tubes (Sysmex Norge, Oslo, Norway). Samples were analyzed with the SENTIFIT-FOB Gold test (Sentinel Diagnostics, Milano, Italy), which is a latex agglutination immunoturbidimetric assay for quantitation of hemoglobin in feces. The assay was applied on an open channel on the Roche Cobas 8000 c702 automated analyzer (Roche Diagnostics, Oslo, Norway). The time of analysis on the Roche Cobas 8000 system was 10 minutes. Diagnostic accuracy and optimal cutoff of the FIT-assay were determined by comparing fecal hemoglobin (f-Hb) concentrations with colonoscopy findings as reference.

The investigators reported that the SENTIFIT-FOB Gold assay showed an imprecision with a total coefficient of variation (CV%) <10% at all concentrations of quality control material and patient sample pools analyzed. At average f-Hb concentrations of 24 ± 0.8 μg/g and 58 ± 2.3 μg/g in patient sample pools the within-run imprecision (repeatability) was 3.4% and 3.9%, respectively. The accuracy of the assay was performed by comparison of the mean quality control sample hemoglobin concentration with the target specified by the manufacturer. The deviation of the mean from the specified target concentration was <4% in both control samples. The Limit of blank (LoB) and Limit of detection (LoD) were estimated to 1 μg/g and 2 μg/g, respectively when using buffer spiked with standard. Using a real patient sample with low f-Hb concentration the LoD was 2 μg/g.

The authors concluded that the SENTIFIT-FOB Gold assay for quantification of hemoglobin in feces applied on the automated Roche Cobas 8000 analyzer shows adequate analytical and clinical performance which agrees well with the performance of the assay on the SENTIFIT-270 analyzer. This enables effective and efficient use of a quantitative FIT on a high-throughput analyzer in large routine clinical chemistry laboratories. In patients presenting with lower abdominal symptoms a cutoff of 10 μg/g seems to be optimal for referral to secondary care and provides a reliable prediction of the absence of CRC and advanced adenoma. The study was published on January 15, 2022 in the journal Practical Laboratory Medicine.

Related Links:
Aalesund Hospital
Sysmex Norge
Sentinel Diagnostics
Roche Diagnostics