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2.4.1 FURTHER INvESTIGATION OF PATIENTS WITH AN INTERMEDIATE PROBABILITy OF
ASTHMA
Patients with airways obstruction
Tests of peak expiratory flow variability, lung volumes, gas transfer, airway hyper-responsiveness
and airway inflammation are of limited value in discriminating patients with established airflow
obstruction due to asthma from those whose airflow obstruction is due to other conditions. 73-
76 Patients may have more than one cause of airflow obstruction, which complicates the
interpretation of any test. In particular, asthma and chronic obstructive pulmonary disease
(COPD) commonly coexist.
; Offer patients with airways obstruction and intermediate probability of asthma a
reversibility test and/or a trial of treatment for a specified period:
if there is significant reversibility, or if a treatment trial is clearly beneficial treat as
asthma
if there is insignificant reversibility and a treatment trial is not beneficial, consider
tests for alternative conditions.*
Patients without airways obstruction
In patients with a normal or near-normal spirogram it is more useful to look for evidence of
airway hyper-responsiveness and/or airway inflammation 71,77-79 These tests are sensitive so
normal results provide the strongest evidence against a diagnosis of asthma.
; In patients without evidence of airways obstruction and with an intermediate probability
of asthma, arrange further investigations* before commencing treatment.
* see section 2.5 for more detailed information on further tests
2 diAGnosis
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