A variety of fecal immunochemical tests (FITs) for hemoglobin are used in colorectal cancer screening.
It is unclear to what extent differences in reported sensitivities and specificities reflect true heterogeneity in test performance or differences in study populations or varying pre-analytical conditions.
Dr Anton Gies and colleagues directly compared the sensitivity and specificity values with which 9 quantitative FITs detected advanced neoplasms in a single colorectal cancer screening study.
Pre-colonoscopy stool samples were obtained from participants of screening colonoscopy in Germany from 2005 through 2010 and frozen at –80°C until analysis.
The stool samples were thawed, homogenized, and used for 9 different quantitative FITs in parallel.
|Screening programs should choose thresholds based on intended levels of specificity |
Colonoscopy and histology reports were collected from all participants and evaluated by 2 independent, trained research assistants who were blinded to the test results.
The team made comparative evaluations of diagnostic performance for advanced neoplasms at preset manufacturers′ thresholds, at a uniform threshold, and at adjusted thresholds yielding defined levels of specificity.
Of the 1667 participants who fulfilled the inclusion criteria, the team reported that all cases with advanced neoplasms and 300 randomly selected individuals without advanced neoplasms were included in the analysis.
The researchers noted that sensitivities and specificities for advanced neoplasms varied widely when they used the preset thresholds or the uniform threshold.
Adjusting thresholds to yield a specificity of 99%, 97%, or 93% resulted in almost equal sensitivities for detection of advanced neoplasms, and almost equal positivity rates.
Dr Gies' team comments, "Apparent heterogeneity in diagnostic performance of quantitative FITs can be overcome to a large extent by adjusting thresholds to yield defined levels of specificity or positivity rates."
"Rather than simply using thresholds recommended by the manufacturer, screening programs should choose thresholds based on intended levels of specificity and manageable positivity rates."