Comparison of spirometry results in adult patients with cystic fibrosis using different reference values

Reference values are needed to interpret spirometry results. The ECCS 1993 reference equations are widely used in Russia. A small proportion of medical facilities have implemented the GLI (2012) reference equations. In 2022, ERS/ATS published recommendations for interpreting spirometry results, which recommend assessing the presence of obstructive disorders by a decrease in FEV1/FVC below the 5th percentile (LLN) and the severity of lung function impairment using a z-score.

The aim. To compare spirometry results in adult patients with cystic fibrosis (CF) in Russia using ECCS and GLI reference values.

Methods. Spirometry in 161 CF adults (70 male/91 female, mean age – 26.3 ± 7.6 years) was used for the comparison. The predicted values, % of predicted values (%pred.) and z-score were calculated. The t-tests were used to compare the ECCS and GLI equations.

Results. Obstructive disorders were detected in 127 (79%) CF patients according to ERS/ATS criteria. Predicted GLI and LLN values were higher for FVC and FEV1, but lower for FEF25–75 and FEF75 in both genders. The %pred and z-score for GLI were significantly lower for FVC and FEV1 compared with the %pred and z-score for ECCS: 79.3%pred and –1.75 vs 83.6%pred and –1.31 (p < 0.001), and 58.7%pred and –3.30 vs 61.2%pred and –3.11 (p < 0.001), respectively. A decrease in FVC and FEV1 was detected using the GLI and ECCS equations in 78 (48.4%) and 130 (80.7%) patients and vs 62 (38.5%) and 124 (77.0%) patients, respectively. In addition, the number of patients with severe impairments in both FVC increased when assessed by GLI versus ECCS (mild: 15% vs 11%, moderate: 22% vs 20%, severe: 12% vs 7%, respectively) and FEV1 (mild: 15% vs 14%, moderate: 23% vs 21%, severe: 43% vs 42%, respectively).

Conclusion. In adult patients with cystic fibrosis, the use of GLI equations is associated with increased detection of both lung function impairment and more severe changes in the spirometric parameters FVC and FEV1. The frequency of lowered FVC and FEV1 statistically significantly increases with the use of GLI. Forced spirometry and detection of a decrease in FEV1/FVC are sufficient to diagnose obstructive disorders.

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