Predicted Values for Spirometry may Underestimate Long-Standing Asthma Severity

BACKGROUND: Asthma may show an accelerated lung function decline. Asthmatics, although having FEV(1) and FEV(1)/VC (and z-scores) higher than the lower limit of normality, may show a significant FEV(1) decline when compared to previous measurements. We assessed how many asymptomatic long-standing asthmatics (LSA) with normal lung function showed a significant FEV(1) decline when an older FEV(1) was taken as reference point. METHODS: 46 well-controlled LSA (age: 48.8±12.1; 23 females) with normal FEV(1) and FEV(1)/VC according to GLI2012 references (FEV(1): 94.8±10.1%, z-score:-0.38±0.79; FEV(1)/VC: 79.3±5.2, z-score:-0.15±0.77) were selected. We considered FEV(1) 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 FEV(1) decline >15% or 30 ml/years was regarded as pathological. RESULTS: When comparing the latest FEV(1) to an at least 5-year-older one (mean 8.1±1.4 years between 2 measurements), 14 subjects (30.4%) showed a FEV(1) decline <5% (mean: -2.2±2.6%), 19 (41.3%) had a FEV(1) 5-15% change (mean: -9.2±2.5%) and 13 (28.3%) a FEV(1) decrease>15% (mean: -18.3±2.4). Subjects with a FEV(1) decline>30 ml/year were 28 (60.8%). When using the highest predicted FEV(1) as reference point and declines were corrected by subtracting the physiological decrease, 6 (13%) patients showed a FEV(1) decline higher than 15%, whereas asthmatics with a FEV(1) loss>30 ml/year were 17 (37%). CONCLUSION: FEV(1) 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.