Forced expiratory volume at 1 second (FEV1)/forced vital capacity (FVC) ratio is the primary diagnostic test.

If normal results and signs and symptoms are consistent with diagnosis, then should undergo pulmonary function tests (PFTs) before and after a methacholine challenge.

FEV1 after bronchodilator should show at least 200 mL and 12% improvement.

FEV1/FVC ratio should be repeated at least once a year.

Moderate sensitivity and high specificity.

A 20% drop in the FEV1 is diagnostic.

If normal results and signs and symptoms are consistent with diagnosis, should undergo PFTs before and after a methacholine challenge.

FEV1 used for subsequent follow-up at least once a year.

If peak flow monitoring is performed, the written asthma action plan should use the patient's personal best peak flow as the reference value.

Long-term daily PEFR monitoring should be considered for: patients who have moderate or severe persistent asthma; patients who have a history of severe exacerbations; patients who poorly perceive airflow obstruction and worsening asthma; or patients who prefer this monitoring method.

Long-term daily PEFR monitoring can be helpful to: detect early changes in disease states that require treatment; evaluate responses to changes in therapy; and afford a quantitative measure of impairment.

PEFR flow monitoring during exacerbations will help determine the severity of the exacerbations and guide therapeutic decisions in the home, school, clinicians' surgery, or emergency department. [1]

Indicated in first presentation to exclude other pathologies, and in acute exacerbations when complicating factors are suspected from history and examination.

May also show signs of infection in acute exacerbation or pneumothorax.

May be considered if spirometry and PEFR do not show reversibility and variability.

Challenge tests to diagnose asthma are divided into: direct (using agents that directly constrict airway smooth muscle (i.e., histamine or methacholine) and indirect (methods or agents that activate mast cells to release mediators such as histamine and leukotrienes to constrict airway smooth muscle, e.g., exercise, eucapnic hyperventilation, inhaled hypertonic saline, mannitol or adenosine monophosphate) challenges. These direct and indirect challenges reflect the baseline fixed (airway remodelling) and episodic variable (inflammatory) components of airway hyper-responsiveness, respectively. [40]

Useful in allergic asthma for identifying allergen and directing immunotherapy.

Results are variable between machines and people.

Most useful in following patient over time.

In combination with sputum eosinophilia, has a high sensitivity and specificity. [41] [42] [43]

Not a standard test in the UK or US at present.