Assessing Intestinal Inflammation: A Comparison of Immunochromatographic Tests and ELISA for Fecal Calprotectin Detection

Background: Fecal calprotectin (FC) is a well-established, non-invasive biomarker of intestinal inflammation and is widely used to differentiate inflammatory bowel disease (IBD) from functional gastrointestinal disorders. Although enzyme-linked immunosorbent assays (ELISA) remain the reference method, rapid immunochromatographic tests (ICTs) offer important operational advantages for point-of-care (POC) diagnostics. However, variability in analytical performance among available ICTs remains a concern. Objective: This study aimed to evaluate the diagnostic accuracy of the CerTest Calprotectin one-step card (CerTest Biotec S.L., Zaragoza, Spain) in comparison with the Actim® Calprotectin lateral flow assay and the reference Calprest® ELISA (Eurospital Diagnostics, Italy). Methods: A total of 128 fresh stool samples from patients clinically suspected of IBD were analyzed in parallel using all three assays. For the reference ELISA (Calprest®), a cutoff value of >40 µg/g was applied according to the manufacturer’s instructions. For discrepant results between assays, a cutoff of 200 ng/mL (equivalent to 200 µg hCp/g stool) was employed for ELISA Calprest® to resolve inconsistencies. The results of the lateral flow assays (CerTest® Calprotectin ICT and Actim® Calprotectin) were interpreted using their respective manufacturer-recommended thresholds. Diagnostic sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using ELISA as the reference standard. Agreement between methods was assessed using Cohen’s κ coefficient. Results: Using ELISA, 47 of 128 samples (36.7%) exceeded the 40 µg/g cutoff. Compared with the Actim® assay, the CerTest card demonstrated a sensitivity of 88.0% (95% CI: 75.7–95.5), a specificity of 100.0% (95% CI: 95.4–100), and a strong agreement (κ = 0.90). When compared with ELISA, the CerTest assay showed a sensitivity of 87.2% (95% CI: 74.3–95.2), a specificity of 96.3% (95% CI: 89.6–99.2), a PPV of 93.2%, an NPV of 93.2%, and a strong agreement (κ = 0.85). Conclusions: The CerTest Calprotectin one-step card provides a rapid and reliable detection of fecal calprotectin, demonstrating a high sensitivity and specificity that are comparable to both other lateral flow assays and the ELISA reference method. These findings support the use of rapid immunochromatographic testing as a valuable tool for preliminary screening and clinical decision-making in patients suspected of IBD, while acknowledging that histology remains the gold standard for definitive diagnosis.