P202 Impact study of 243 indirect bronchial provocation tests with mannitol in the diagnosis and management of asthma

Abstract

Introduction: and Objective Our lung investigation unit introducedindirect bronchial provocation challenge tests with mannitol toreplace direct bronchial provocation tests with Methacholine Mannitol challenge tests have practical and safety profile advantages.The sensitivity and specificity for PC20 Methacholine are 91%(84.2%-97.8%) and 90% (76.9%-100%) respectively.1 The specificityof PD15 Mannitol compares well to Methacholine at 98.4%(96.2%-99.4%), but the sensitivity of PD15 Mannitol is lower at58.8% (50.7%-62.6%).2 The aim of the study was to review theclinical interpretation of mannitol challenge test results in thediagnosis of asthma. Methods: Data were collected on all Mannitol challenge testsperformed between July 2008 and January 2011. A retrospectiveanalysis of case notes was performed to assess the indication for thetest, the interpretation of results and any subsequent changes inmanagement. Results: 243 tests were performed and 240 sets of data analysed, 3 setsof case notes could not be obtained. 147 (61%) patients presentedwith wheeze and dyspnoea with a possible diagnosis of asthma, 48/134 (36%) tests were positive confirming the diagnosis and 13 (8.8%)patients were unable to performthe test. 89 (37%) patients presentedwith cough, 20/86 (23.3%) tests were positive and three patients wereunable to perform the test. 68/69 (99%) of the positive mannitol testswere interpreted as confirmation of the diagnosis of asthma. The 155negative tests were interpreted as false negative in 20 (13%) patients.In 87 (56%) cases additional tests were subsequently performed andan alternative diagnosis was made and in 48 (31%) cases the resultwas interpreted as true negative. Three of these patients (6%) representedand were subsequently diagnosed with asthma.Conclusion Mannitol challenge tests are useful in confirming thediagnosis of asthma in patients with high pre-test probability of thedisease. Physicians need to recognise the risk of false negativemannitol test results and perform additional tests when the diagnosisis uncertain and clinical suspicion remains high. (Graph presented)