Time-resolved fluorimetric immunoassay of calprotectin: technical and clinical aspects in diagnosis of inflammatory bowel diseases

Background: Growing evidence in the literature shows the clinical importance of the calprotectin assay in faeces, especially for the differential diagnosis and monitoring of patients with inflammatory bowel diseases. Methods: We developed a time-resolved fluorimetric immunoassay for calprotectin to extend the limited measuring range of the commercially available ELISA method currently used in our laboratory. Together with the introduction of a non-enzymatic label, this new method offers the advantages of better precision and higher sensitivity. Results: The new assay shows a dynamic measuring range extended by a factor four, which reduces the number of samples with concentrations outside the measuring range from 30% to only 4%. The value of the assay was confirmed in various patient groups suffering from active and inactive gastrointestinal diseases. We suggest that the frequent coincidence of a high calprotectin concentration with intestinal blood loss is not the consequence of mere blood loss, but can be ascribed to neutrophil infiltration and subsequent shedding into the intestinal lumen as a result of intestinal inflammation or malignancy. Conclusion: We expect that in the near future faecal calprotectin will be used as a non-invasive routine diagnostic marker and an effective laboratory parameter to monitor patients with inflammatory bowel disease.