Methodological considerations on ‘an international collaborative initiative to screen primary ciliary dyskinesia with high-speed video microscopy and nasal nitric oxide at a tertiary referral centre in South India’

Dear Editor, We read with interest the article by Benjamin et al.[1] describing an international collaborative initiative to screen patients with suspected primary ciliary dyskinesia (PCD) using high-speed video microscopy analysis (HSVA) and nasal nitric oxide (nNO) testing at a tertiary referral centre in South India. The authors should be commended for addressing an important gap in diagnostic access for PCD in resource-limited settings. Nevertheless, several methodological and reporting aspects of the study warrant further consideration when interpreting the findings. Firstly, the recruitment strategy may introduce selection bias. Participants were enrolled from a tertiary referral centre based on clinical suspicion of PCD. Referral-based sampling commonly includes patients with more complex or persistent respiratory symptoms and may therefore overestimate the proportion of screen-positive cases. In the present study, 60.1% of patients were classified as PCD screen-positive. Observational research guidelines emphasise the importance of clearly defined sampling strategies and representative populations to ensure that findings can be interpreted appropriately and generalised beyond the study setting.[2] Secondly, the classification of patients as “PCD screen-positive” when either HSVA or nNO was abnormal requires careful interpretation. Current international guidelines from the American Thoracic Society and European Respiratory Society recommend that the diagnosis of PCD should rely on a combination of diagnostic tests interpreted within a structured algorithm, rather than a single abnormal screening result.[3] Abnormal ciliary motility or low nNO values may occasionally occur in conditions such as secondary ciliary dysfunction or temporary epithelial injury during respiratory infections. Studies evaluating diagnostic pathways for PCD emphasise that combining multiple complementary tests improves diagnostic accuracy and reduces the risk of misclassification.[4] Further, genetic confirmation was performed in only a subset of screen-positive patients because of financial constraints. While this reflects real-world challenges in low-resource settings, selective application of confirmatory testing may introduce verification bias. Verification bias occurs when the reference standard test is applied only to selected participants and can lead to inaccurate estimation of diagnostic performance.[5] Ensuring more uniform confirmatory testing would provide a clearer assessment of the screening strategy’s effectiveness. Additionally, the statistical analysis presented in the study is largely descriptive. Although summarising patient characteristics using medians and percentages provides an overview of the cohort, further analytical evaluation could strengthen the study’s conclusions. Diagnostic research often benefits from analyses such as sensitivity, specificity, predictive values, or agreement between diagnostic methods, which provide more direct insight into the clinical usefulness of screening tests.[6] Finally, the study reports that a substantial number of HSVA samples were inconclusive due to inadequate specimen quality. Additional details regarding repeat sampling, quality-control procedures, or how these inconclusive cases were managed would improve transparency and reproducibility. Diagnostic studies benefit from detailed reporting of such methodological aspects to allow readers to better evaluate the robustness of the findings. In conclusion, the study by Benjamin et al.[1] contributes valuable preliminary evidence regarding PCD screening in a resource-limited setting. Addressing the methodological considerations outlined above would further strengthen the interpretation of the findings and support future research aimed at improving diagnostic pathways for PCD. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.