Predicted Values for Spirometry may Underestimate Long-Standing Asthma Severity

Abstract

Background: Asthma may show an accelerated lung function decline. Asthmatics, although having FEV1 and FEV1/VC (and z-scores) higher than the lower limit of normality, may show a significant FEV1 decline when compared to previous measurements. We assessed how many asymptomatic long-standing asthmatics (LSA) with normal lung function showed a significant FEV1 decline when an older FEV1 was taken as reference point. Methods: 46 well-controlled LSA (age: 48.8±12.1; 23 females) with normal FEV1 and FEV1/VC according to GLI2012 references (FEV1: 94.8±10.1%, z-score:-0.38±0.79; FEV1/VC: 79.3±5.2, z-score:-0.15±0.77) were selected. We considered FEV1 decline, calculated by comparing the latest value to one at least five years older or to the highest predicted value measured at 21 years for females and 23 for males. A FEV1 decline >15% or 30 ml/years was regarded as pathological. Results: When comparing the latest FEV1 to an at least 5-year-older one (mean 8.1±1.4 years between 2 measurements), 14 subjects (30.4%) showed a FEV1 decline <5% (mean: -2.2±2.6%), 19 (41.3%) had a FEV1 5-15% change (mean: -9.2±2.5%) and 13 (28.3%) a FEV1 decrease>15% (mean: -18.3±2.4). Subjects with a FEV1 decline>30 ml/year were 28 (60.8%). When using the highest predicted FEV1 as reference point and declines were corrected by subtracting the physiological decrease, 6 (13%) patients showed a FEV1 decline higher than 15%, whereas asthmatics with a FEV1 loss>30 ml/year were 17 (37%). Conclusion: FEV1 decline calculation may show how severe asthma actually is, avoiding a bronchial obstruction underestimation and a possible under-treatment in lots of apparent “well-controlled” LSA with GLI2012-normal-range lung function values.