Asthma diagnosis is largely clinical, but it is important that diagnosis is backed up with objective testing. Unfortunately about a third of patients who have been given a diagnosis of asthma, don’t actually have a diagnosis when they are evaluated with objective tests.
Spirometry with reversibility is the gold-standard objective test for asthma. In patients with asthma who are currently experiencing bronchoconstriction, you would expect to see an abnormal spirometry and a significant improvement in FEV1 of more than 12% or 200ml when you perform a reversibility assessment. Some patients may experience an even greater improvement in FEV1 following administration of a bronchodilator. If the patient experiences a 400ml improvement in FEV1, the diagnosis is much more secure.