Diagnostic accuracy of the combination of fecal calprotectin and occult blood tests in inflammatory bowel disease

INTRODUCTION: This study aimed to assess the diagnostic accuracy of the fecal occult blood test (FOBT), fecal calprotectin (FC), and the combination of these markers in patients with suspected inflammatory bowel disease (IBD). Additionally, FC levels were compared between patients monitored for IBD and those newly diagnosed with IBD.
METHODS: Conducted at Gazi University Application and Research Hospital, this retrospective study reviewed demographic, clinical, colonoscopy reports, and laboratory data (FC and FOBT) of IBD patients. The final analysis included 153 patients with suspected IBD to evaluate the diagnostic accuracy of FOBT, FC, and their combination. FC was analyzed using the Quantum Blue® fCAL extended test. The ROC curve was drawn to determine the diagnostic ability of FC, and the area under the curve (AUC) was calculated. Sensitivity, specificity, and predictive values were determined for FC and FOBT.
RESULTS: The AUC was determined as 0.827 (95% CI: 0.742–0.913) for FC (p<0.001). FC showed a sensitivity of 85.7%, specificity of 62.4%, positive predictive value (PPV) of 30.6%, and negative predictive value (NPV) of 95.8%. FOBT had a sensitivity of 81.3%, specificity of 78.1%, PPV of 30.2%, and NPV of 97.3%. The combination of FOBT and FC, with positivity in at least one of the tests, had a sensitivity of 93.8%, specificity of 63.5%, PPV of 23.1%, and NPV of 98.9%. The combined use of FOBT and FC demonstrated higher diagnostic accuracy than either test alone.
DISCUSSION AND CONCLUSION: The combination of FOBT and FC provides superior diagnostic accuracy for identifying suspected IBD
patients compared to each test alone. This combined approach could serve as a cost-effective strategy to avoid unnecessary invasive procedures.