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Joana Belo1, Pedro Martins1,2, Isabel Peralta1, Sara Serranho1, Nuno Neuparth1,2, Paula Leiria Pinto1,2

1- Serviço de Imunoalergologia, Hospital de Dona Estefânia, Centro Hospitalar de Lisboa Central, EPE
2- CEDOC, NOVA Medical School / Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Portugal

- European Academy of Allergy and Clinical Immunology Congress 2015, 6-10 June, Barcelona, Spain
- Apresentação sob a forma de poster discussion session; publicação de resumo
- Reunião Internacional

Background: In the last decade several studies have questioned the use of fixed criteria in the interpretation of lung function tests (LFT). The Global Lung Function Initiative (GLI) proposed the use of unifying reference equations, based on the lower limit of normal (LLN) to define airway obstruction.
Aim: To compare the theoretical values obtained through the reference equations routinely used in our hospital’s lung function laboratory (Equation 1) and those obtained with GLI’s equations (Equation 2). The association of bronchial obstruction and the lack of asthma control was also studied.
Methods: 367 individuals with physician diagnosed asthma were evaluated through spirometry and performance of Asthma Control Tests (ACT). A comparison of the theoretical values of the equations using Bland-Altman’s agreement test was also performed. The association of each of these criteria with the absence of asthma control (ACT < 20) was studied.
Results: Half of the individuals in our sample were males (50.1%), with a median age of 18 years old (p25-p75: 14-30 years old). Regarding Equation 1, 9% (n = 33) presented a FEV1< 80%.  In Equation 2, 16.7% (n = 61) had a FEV1< 80%, 15.8% (n = 58) had a FEV1 < LLN, 20.8% (n = 76) had a FEV1/FVC < LLN and 12% (n = 44) presented a FEV1/FVC < 0.70. Regarding the ACT, 22.6% (n = 83) patients lacked asthma control. The average of the differences between Equation 1 and equation 2 was 8.5% (± 1.96 SD: -5.4% to 22.4%). The absence of asthma control had significant associations with FEV1< LLN (p = 0.003), FEV1<80% (p=0.015) and FEV1/FVC < LLN (p = 0.003) of the equation 2. An association was found between a FEV1/FVC < 0.70 and an ACT score < 20 (p = 0.008).
Conclusions: The mean differences found between the two reference equations should be considered in the interpretation of the LFT. Although there is no available information regarding the suitability of the GLI equations to the Portuguese population, our results suggest that the use of the FEV1 LLN is a useful criterion in the assessment of the degree of asthma control.

Palavras Chave: lung function tests, airway obstruction, reference equations