Limitations of PICADAR as a diagnostic predictive tool for primary ciliary dyskinesia

Background: The Primary Ciliary Dyskinesia Rule (PICADAR) is a diagnostic predictive tool currently recommended by the European Respiratory Society (ERS) to assess the likelihood of a primary ciliary dyskinesia (PCD) diagnosis. Despite its recommendation according to the current ERS PCD diagnostic guideline, the performance of the PICADAR remains insufficiently studied. Methods: We evaluated the sensitivity of PICADAR in 269 individuals with genetically confirmed PCD. Using an initial question, PICADAR rates all individuals without daily wet cough negative for PCD. PICADAR evaluates seven questions in the daily wet cough group. We here calculated test sensitivity based on the proportion of individuals scoring ≥5 points as recommended. Subgroup analyses examined the impact of laterality defects and predicted hallmark ultrastructural defects. Results: 18 individuals (7%) reported no daily wet cough ruling out PCD according to PICADAR. The median PICADAR score was 7 (IQR: 5–9), with an overall sensitivity of 75% (202/269). Sensitivity was higher in individuals with laterality defects (95%; median score: 10; IQR 8–11) compared to those with situs solitus (61%, median score: 6; IQR 4–8; p*<0.0001). Further stratification by associated ciliary ultrastructure showed higher sensitivity in individuals with hallmark defects (83%) versus those without (59%, p*<0.0001). Conclusion: The PICADAR has limited sensitivity, particularly in individuals without laterality defects (61%) or absent hallmark ultrastructural defects (59%). Therefore, PICADAR should not be the only factor to initiate diagnostic work-up for PCD. Alternative predictive tools are needed, particularly for PCD individuals with normal body composition and normal ultrastructure.