Comparison of spirometric reference values in Chilean children

Background: The interpretation of lung function tests must be based on reference normal values obtained in the same population. In Chile an expert panel recommended the use of values obtained by Gutierrez et al locally, that are higher than those obtained by Knudson, for forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1). Aim: To analyze the clinical application of both reference values in a selected population. Material and methods: Retrospective review of 499 spirometries done in our laboratory to 285 males and 214 females, aged 4.5 to 18 years. The reports using either Gutierrez (G) or Knudson (K) reference values were compared. The 5th percentile was considered the inferior limit for normality. Results: The height range of patients was 110-178 cm (median 130, 3rd quartile 143). Referral diagnoses were probable asthma in 349 (70%), asthma in 119 (24%), to rule out restrictive disease in 12 (2%) and others 19 (4%). FEV1/FVC ratio was greater than or equal to84% in 290 patients. Using K values, lung function was interpreted as within normal limits in 321 patients (64.3%), as mild obstructive disease (MOD) in 171 (34.3%), as combined limitation (CL) in 2, mild restrictive disease (MRD), moderate restrictive disease (MR) and severe restrictive disease (SRD) in 1 patient each. Using G values, lung function was interpreted as within normal limits in 133 patients (26.7%), MOD in 343 (68.7%), MRD in 6, CL in 4 and MR in 2. In 193 spirometries (39%) there was lack of concordance between the interpretations using K or G values. Conclusions: There is a wide rante of variability when G or K values are used to interpret lung function in children in Chile. Redefinition of local standards would be necessary.