Late Breaking Abstract - Assessing the diagnostic accuracy of home spirometry system for asthma diagnosis

Home spirometry systems that measure daily lung function variability can enhance asthma diagnosis. The objective was to evaluate the diagnostic accuracy of spirometry with reversibility test; daily peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) variability tests; and trial treatment for uncertain cases. Subjects with asthma-like symptoms from seven primary healthcare centers in Sweden, underwent spirometry with reversibility testing, 2-4 weeks of diurnal PEF and FEV1 testing using home spirometry system (AsthmaTuner), and trial treatment. Sensitivity and specificity were calculated to evaluate diagnostic test performance for doctor’s documented asthma diagnosis. Of 146 subject, 123 (84%) had complete information about diagnosis, and 4% had used controller treatment. Of 123 subjects, 71 (58%) were diagnosed with asthma, 6 were diagnosed after trial treatment, and 52 (42%) did not have asthma. Reversibility tests (FEV1 >12% and 200 ml) were positive in 6/123 (5%) subjects. Diurnal FEV1 and PEF variability (>10%) were more common in diagnosed asthma cases compared with no asthma, FEV1: 75% vs. 56%, PEF: 91% vs. 64%, p-values <0.018, <bold>Figure 1</bold>. Reversibility testing had low sensitivity for asthma 28% (95% CI: 18%-40%), but high specificity 81% (67%-90%). At least two days of positive diurnal variability tests showed highest sensitivity and specificity, respectively, for asthma diagnosis: FEV1: 61% (95% CI: 48%-72%) and 58% (43%-71%); PEF: 76% (64%-85%) and 69% (55%-81%). In conclusions, most subjects with asthma-like symptoms were diagnosed with reversibility and diurnal variability testing. Variability testing demonstrated the highest levels of sensitivity and specificity.