Is spirometry essential in diagnosing asthma? No.

Asthma is a chronic respiratory disease characterised by fluctuating respiratory symptoms and reversible airflow obstruction.1,2 Confirmation of the diagnosis hinges on demonstrating airflow obstruction varying over time. Patients with undiagnosed asthma who consult repeatedly with symptoms ranging in severity3 may demonstrate perfectly normal spirometry. As there is no single ‘gold standard’ test, clinical asthma diagnosis is based on evidence of recurrent respiratory symptoms; reversibility with anti-asthma treatment; and variable airflow obstruction. Demonstrating any, or all three, of these features in a clinical setting is challenging: the disease fluctuates. The diagnosis is clear cut if spirometry in a patient with a history suggestive of asthma demonstrates airflow obstruction with reversibility. However, if the test is normal, asthma cannot be excluded. Is spirometry the most practical test? It would be, if patients could guarantee to exhibit airflow obstruction at the time spirometry is performed; clearly they can not, and this practical and logistic issue limits the feasibility and usefulness of this investigation in every case. Peak expiratory flow (PEF) and spirometry are both widely accepted as investigations for determining the presence of airflow obstruction.1,2 Because variability and reversibility are features of asthma, a normal spirogram or PEF measurement obtained in an asymptomatic patient does not exclude asthma. The challenge, then, is to obtain evidence of intermittent airflow obstruction; serial PEF diary entries offer a practical alternative to a single clinic lung function test. Although FEV1 is more reliable1 than and preferable2 to measurement of PEF (because it allows clearer identification of airflow obstruction), it is not essential for diagnosing asthma. Quality-assured, reliable spirometry requires a well-trained, competent operator; properly maintained and calibrated equipment; and a cooperative patient able to closely reproduce results.4 In contrast, PEF is measured using a simple cheap meter requiring less cooperation by the patient. Reliability of PEF readings can be increased by training and ensuring that patients have their own meter, as the readings between meters may vary.