The characteristics of different diagnostic tests in adult mild asthmatic patients: Comparison with patients with asthma-like symptoms by gastro-oesophageal reflux

SummaryBackgroundDiagnosing asthma cannot be always easy. It is important to consider the validity of the diagnostic tests, and/or how much more commonly they are positive in patients with asthma compared to healthy subjects and, particularly, to patients with asthma-like symptoms.ObjectiveTo evaluate the validity of diagnostic tests for asthma, in terms of sensitivity, specificity, positive and negative predictive values, in patients with bronchial asthma compared to patients affected by gastro-oesophageal reflux disease (GERD) with asthma-like symptoms, and healthy control subjects without asthma and gastro-oesophageal reflux (GER).DesignSingle-center, cross-sectional, observational study.PatientsWe studied 60 patients with mild asthma, 30 patients with GERD and asthma-like symptoms and 25 healthy control subjects.MeasurementsWe measured provocative concentration of methacholine causing a 20% fall in the forced expiratory volume in 1 s (MCh PC20/FEV1), the amplitude percent mean of peak expiratory flow (A%M of PEF), derived from twice-daily readings for >2 weeks, the FEV1/forced vital capacity (FEV1/FVC) ratio, the eosinophil count in blood and in induced sputum and the serum eosinophil cationic protein (ECP) levels.ResultsFEV1/FVC ratio, A%M of PEF, blood eosinophils counts and serum ECP levels were less sensitive and specific when the reference population was composed of patients with asthma-like symptoms by GER. While, MCh PC20/FEV1 and induced sputum eosinophils count were the most sensitive (both 90%) and specific (89% and 92%, respectively) tests.ConclusionOur findings demonstrate that MCh PC20/FEV1 and the induced sputum eosinophil count are the most useful objective tests in patients with mild asthma. All patients with asthma presented both an MCh PC20/FEV1 <1500 μg and eosinophils count in the induced sputum >1%.