From the Guidelines
Asthma diagnosis typically involves pulmonary function tests (PFTs) such as spirometry, which can show reversible airflow obstruction, and/or challenge tests that demonstrate increased airway sensitivity.
Key Labs for Asthma Diagnosis
- Spirometry: to assess for reversible airflow obstruction, a key characteristic of asthma 1
- Bronchodilator responsiveness test: to evaluate for improvement in lung function after administration of a bronchodilator, indicating asthma 1
- Bronchial challenge test: to assess for airway hyperresponsiveness, a hallmark of asthma 1
- Fractional exhaled nitric oxide (FeNO): can support a diagnosis of asthma, particularly in cases where spirometry is normal or inconclusive 1
- Peak flow diaries: a practical alternative for monitoring asthma symptoms and response to treatment in primary care settings 1
Additional Considerations
- Chest x-ray: may be needed to exclude other diagnoses, such as pulmonary embolism or congestive heart failure 1
- Biomarkers of inflammation: such as total and differential cell count and mediator assays in sputum, blood, urine, and exhaled air, are being evaluated for their usefulness in asthma diagnosis and assessment 1
From the Research
Laboratory Tests for Asthma
The following laboratory tests are used to diagnose and monitor asthma:
- Spirometry with bronchodilator reversibility testing: This is the mainstay of asthma diagnostic testing for children and adults 2
- Repeated peak flow measurement: This is a simple test that can be implemented in a clinical and home setting to monitor asthma symptoms 2
- Bronchial challenge testing: This test is reserved for patients in whom the aforementioned testing has been unrevealing but clinical suspicion remains 2
- Fractional exhaled nitric oxide measurement: This test can help identify eosinophilic inflammation, which is supportive of atopic asthma 2, 3
- Blood eosinophil count: This test can help identify eosinophilic asthma, with a cut-off of 2.7% being a good predictor of eosinophilic asthma 4
- Blood neutrophil count: This test can help identify neutrophilic asthma, but with less accuracy than blood eosinophil count 4
Biomarkers for Asthma
The following biomarkers are used to investigate and stratify asthma:
- Blood eosinophil count: This biomarker can help identify type 2 airway inflammation and guide treatment decisions 3
- Fractional exhaled nitric oxide: This biomarker can help identify eosinophilic inflammation and guide treatment decisions 3
- Eosinophil/lymphocyte ratio (ELR) and eosinophil/neutrophil ratio (ENR): These biomarkers can help predict eosinophilic asthma 4
- Neutrophil/lymphocyte ratio (NLR): This biomarker can help detect neutrophilic asthma, but with less accuracy than blood eosinophil count 4