SESSION TITLE: Asthma - Bronchiectasis Posters
SESSION TYPE: Original Investigation Poster
PRESENTED ON: Wednesday, October 28, 2015 at 01:30 PM - 02:30 PM
PURPOSE: In suspected asthmatics, methacholine challenge test (MCT) would frequently be done to aid in diagnosis and management if initial spirometry was normal with lack of bronchodilator reversibility (BDR). Studies have suggested a reduced FEF25-75 may be an early indicator of small airway disease. We wanted to explore the relationship between FEF25-75 values and bronchial hyper-reactivity as determined by MCT to better define role of FEF25-75 in suspected asthmatics in Singapore.
METHODS: This was a retrospective study of patients with suspected asthma who had normal spirometry with no BDR and subsequent MCT performed. Patients were identified from our lung function database at Changi General Hospital for a 1-year period from 1st Jan 2012. 3 spirometric parameters were collected, namely, pre-bronchodilator FEF25-75 in percentage (%) predicted, absolute volume change between pre- & post-bronchodilator FEF 25-75 in liters and change in % predicted between pre- & post- FEF25-75. We also recorded whether MCT was positive based on a PC20 reading of ≤ 16 (mg/ml).
RESULTS: 161 patients were included in this study, of which 30.4% had positive MCT. 59.0% of 161 patients were male. There was statistically significant lower mean pre-FEF25-75 in MCT positive patients compared to MCT negative patients, 66.5% ± 25.5% vs 89.7% ± 26.1% respectively (p<0.001). We used receiver operating characteristic (ROC) curve to assess diagnostic performance of the three FEF25-75 parameters in predicting MCT positivity. Pre-bronchodilator FEF25-75 performed best with area under curve (AUC) of 0.767. Optimal cut-off maximizing sensitivity and specificity for preFEF25-75 was 76.0%. Using pre FEF25-75 of ≤ 76.0% to predict MCT positivity had calculated sensitivity and specificity of 73.5% and 74.1%. It also had best negative predictive value of 86.5% but positive predictive value (PPV) was only 55.4%. AUC for absolute volume change between pre & post FEF25-75 and % predicted change between pre & post FEF25-75 was 0.533 and 0.631 respectively. In this study, pre FEF25-75 of ≤55% predicted had best PPV of 69.2%. Combining various FEF25-75 parameters did not improve accuracy of predicting MCT positivity.
CONCLUSIONS: These findings imply FEF25-75 values cannot reliably predict MCT positivity and a reduced FEF25-75 value alone should not be used to diagnose asthma.
CLINICAL IMPLICATIONS: However, if pre-test probability of asthma is low, pre FEF25-75 more than 76.0% predicted can be used to rule out asthma as MCT is also likely to be negative.
DISCLOSURE: The following authors have nothing to disclose: Xue Ning Choo, Corrine Kang, Tunn Ren Tay, Hang Siang Wong
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