Use clinical tests to diagnose asthma and to avoid overdiagnosis, says NICEBMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h522 (Published 29 January 2015) Cite this as: BMJ 2015;350:h522
Doctors should use clinical tests to accurately diagnose asthma rather than simply taking a medical history, the National Institute for Health and Care Excellence (NICE) has said, because around 1.2 million UK adults may be wrongly receiving treatment for the condition.
No gold standard test is currently available to diagnose asthma, and in current practice doctors mainly check for signs and symptoms. But NICE said that almost a third of people being treated for asthma do not have clear evidence of the condition. Some may have had asthma in the past, NICE added, but it is likely that many have been given an incorrect diagnosis.
New draft guidelines from NICE1 show in simple flowcharts the clinical tests that doctors should use to diagnose asthma more accurately. They state that doctors should take a structured clinical history but should not use symptoms alone, or a history of atopic disorders alone, to diagnose asthma. Asthma should also not be diagnosed on the basis of any single diagnostic test alone, the guidelines advise.
Spirometry should be used as the first line investigation for asthma in adults and in children over 5, the draft guidance says. A forced expiratory volume in one second to forced vital capacity (FEV1/FVC) ratio of less than 70% should be considered a positive test for obstructive airway disease. These patients should then be offered a bronchodilator reversibility test, which measures the ability to reverse obstruction in the airways by using bronchodilators. An improvement in FEV1 of 12% or more, together with an increase in volume of 200 mL or more, should be considered a positive test.
A fractional exhaled nitric oxide test (FeNO) should be offered to over 16s if a diagnosis of asthma is being considered, where a FeNO level of 40 parts per billion or more is considered a positive test. And a direct bronchial challenge test with histamine or methacholine should be offered to adults and over 16s if there is diagnostic uncertainty.
In children under 5, doctors should treat symptoms on the basis of observation and clinical judgment until the child is old enough to have clinical tests, the guidelines say.
They also recommend that doctors should ask people whether their symptoms are better on days away from work, as around a 10th of adults with asthma develop the condition because they are exposed to certain substances such as chemicals or dust in their workplace.
Mark Baker, director of clinical practice at NICE, said, “Accurate diagnosis of asthma has been a significant problem which means that people may be wrongly diagnosed or cases might be missed in others.
“Our aim with this guideline is to give clarity and set out the most clinical and cost effective ways to diagnose and monitor asthma based on the best available evidence.”
Cite this as: BMJ 2015;350:h522