Diagnostics

Asthma can be diagnosed in patients ≥ 5 years of age, based on a combination of: [13]

• Typical clinical features of asthma

• Demonstration of reversible bronchial obstruction

  • First-line: PFTs

  • Second-line (if initial PFTs are inconclusive): bronchial provocation tests

Consider adjunctive studies as needed:

• To identify common comorbidities

• To exclude differential diagnoses of asthma

Diagnostics for acute asthma are covered separately.

Characteristic findings (observable using any of the PFT modalities described below)

• An obstructive pattern of airflow limitation (see “Obstructive lung diseases”)

• Reversibility of airflow obstruction on bronchodilator administration

• Excessive variability of lung function parameters (FEV1, PEFR) on repeat testing

Allergy workup: Consider if allergens are suspected to play a significant role in exacerbations.

• Skin allergy tests: skin prick testing (SPT) or intradermal skin testing

• CBC: possible eosinophilia

• Antibody testing, total IgE (increased), allergen-specific IgE (increased)

Evaluation for additional asthma triggers: e.g., see “Rhinitis”, “Sinusitis”, “GERD” [3]

Additional diagnostic studies (not routinely recommended)

• Sputum analysis revealing one or more of the following:

  • Curschmann spirals: whorled mucous plug in sputum that is formed by shed bronchial epithelium

  • Charcot-Leyden crystals: histopathologic finding in patients with eosinophilic inflammation and/or proliferation

  • Creola bodies: aggregate of desquamated epithelial cells [14]

• Single-breath diffusion capacity: normal or ↑ DLCO

• Fractional exhaled nitric oxide (FeNO)

  • The concentration of nitric oxide in exhaled air.

  • Usually elevated in response to airway inflammation (e.g., allergic/eosinophilic asthma, atopy, eosinophilic bronchitis)

  • Although not routinely recommended, FeNO measurement may be useful for distinguishing between inflammatory and noninflammatory asthma and guiding allergic asthma treatment; higher FeNO levels indicate more inflammation and the potential need to escalate therapy.

  • May be elevated in allergic asthma