From the Guidelines
Nasal nitric oxide measurement alone is not sufficient for diagnosing primary ciliary dyskinesia (PCD). While it is a valuable screening tool with high sensitivity, a definitive diagnosis of PCD requires a combination of tests, as recommended by the American Thoracic Society clinical practice guideline 1. Nasal nitric oxide measurement should be used in conjunction with other diagnostic methods such as genetic testing, transmission electron microscopy of ciliary ultrastructure, and high-speed video microscopy of ciliary beat pattern and frequency.
The European Respiratory Society guidelines also support the use of a combination of tests for diagnosing PCD, including nasal nitric oxide measurement, high-speed video microscopy analysis, and transmission electron microscopy 1. A low nasal nitric oxide level (typically below 77 nL/min) may suggest PCD, but it can also occur in other conditions like cystic fibrosis or acute sinusitis. To confirm a PCD diagnosis, patients with low nasal nitric oxide levels should undergo further testing, including genetic analysis for known PCD-causing mutations and direct examination of ciliary structure and function.
Some key points to consider when diagnosing PCD include:
- The use of a panel of diagnostic tests to increase diagnostic certainty and differentiate PCD from other conditions with similar symptoms 1
- The importance of considering the clinical phenotype and medical history of the patient when interpreting diagnostic test results
- The need for referral to a PCD specialty center for comprehensive evaluation and testing, if necessary
- The potential for international differences in diagnostic test availability and the need for providers to consider diagnostic options based on availability 1.
Overall, a multi-test approach is necessary for accurate diagnosis of PCD, and nasal nitric oxide measurement alone is not sufficient for diagnosing this complex and heterogeneous disorder.
From the Research
Diagnostic Accuracy of Nasal Nitric Oxide Measurement
- The diagnostic accuracy of nasal nitric oxide (nNO) measurement for primary ciliary dyskinesia (PCD) has been evaluated in several studies 2, 3, 4, 5.
- A meta-analysis found that nNO measurement has high sensitivity (97.6%) and specificity (96.0%) for diagnosing PCD, with a positive likelihood ratio of 24.3 and a negative likelihood ratio of 0.03 4.
- Another study found that nNO measurement has a sensitivity of 95% and specificity of 94% for diagnosing PCD, with a positive likelihood ratio of 15.8 and a negative likelihood ratio of 0.06 2.
Practical Issues in Children
- Nasal nitric oxide measurement can be used for early diagnosis of PCD in children, but practical issues such as cooperation and age need to be considered 5.
- Healthy children have higher nNO levels than PCD patients, but low nNO levels can be found in uncooperative healthy children, which may increase with repeated evaluations 5.
Limitations and Potential Dangers
- While nNO measurement is a useful test for PCD, it is not perfect and can produce false positives, particularly in more general populations 6.
- The predictive values of nNO testing can be good in referral populations, but may be poor in more general populations, potentially overwhelming diagnostic services 6.
- A normal nNO result with a classical clinical history should still be considered for further testing 6.