Predicted Values for Spirometry may Underestimate Long-Standing Asthma Severity

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.

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.

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%).

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.