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Basic variables at different positivity thresholds of a quantitative immunochemical test for faecal occult blood
G Castiglione1, G Grazzini, G Miccinesi
1Centro per lo Studio e la Prevenzione Oncologica, Istituto Scientifico della Regione Toscana, Viale A Volta 171, I-50131 Firenze, Italy. g.castiglione@cspo.it
Journal of Medical Screening
|October 9, 2002
Summary
Adjusting the positivity threshold for fecal occult blood tests (FOBT) impacts colorectal cancer (CRC) screening. Higher thresholds reduce false positives but miss more cancers, while lower thresholds increase detection but also recall rates.
Area of Science:
- Gastroenterology
- Oncology
- Medical Diagnostics
Background:
- Faecal occult blood testing (FOBT) is a proven method for reducing colorectal cancer (CRC) mortality and incidence.
- Immunochemical FOBTs offer better cost-effectiveness than guaiac-based tests.
- The latex agglutination test (LAT) is a fully automated, quantitative FOBT method.
Purpose of the Study:
- To evaluate the performance of the latex agglutination test (LAT) for colorectal cancer (CRC) screening across various positivity thresholds.
- To determine the impact of different LAT positivity thresholds on positivity rates, detection rates, and positive predictive values.
Main Methods:
- A population-based screening program utilized LAT as the standard FOBT for individuals aged 50-70.
- The standard positivity threshold for LAT was 100 ng hemoglobin/ml.
- Positivity rates, detection rates for CRC and high-risk adenomas, and positive predictive values were calculated for multiple thresholds.
Main Results:
- Increasing the LAT positivity threshold from 100 to 200 ng/ml decreased positivity rates.
- Higher thresholds led to decreased detection rates for CRC and high-risk adenomas.
- Positive predictive values for cancer and high-risk adenomas increased with higher thresholds.
Conclusions:
- Raising the LAT positivity threshold reduces recall rates and improves positive predictive value but significantly lowers cancer detection rates.
- Decreasing the threshold increases recall rates and screening sensitivity.
- Optimal LAT positivity threshold requires further evaluation, especially regarding sensitivity for interval cancers.