A retrospective investigation of air flow limitation accounted according to Z-score in the relationship to short-TERM mortality in patients with chronic obstructive pulmonary disease

COPD (Chronic Obstructive Pulmonary Disease) can be diagnosed by detecting the presence of chronic airflow limitation as a result of spirometric examination. GOLD guidelines recommend the use of post-bronchodilator FEV1/FVC<0.70 to diagnose patients with chronic respiratory symptoms or at risk. Spirometry; It is used in confirming the diagnosis of COPD, in differential diagnosis with other diseases, in evaluating the course and prognosis of the disease in diagnosed patients and in monitoring the treatment response to the disease. The use of appropriate reference tests is necessary when interpreting pulmonary function test parameters and generally the selected reference values are considered the expected value and the individual's measured pulmonary function parameters are expressed as a percentage of the expected value for that individual. Many reference equations have been defined since 1971. GLI (Global Lung Function Initiative) was established by ERS in 2010 to investigate the variation among existing reference equations and to define new reference equations. In 2012, new age-appropriate LLN (Lower Limits of Normal) and expected reference values that can be used in the 3-95 age range were defined by the GLI. In addition, it was thought that it would be a better approach to express the measurement results as z-scores and include the age-specific normal range in the reports. Accordingly, the presence of GLI airflow limitation suggests that FEV1/FVC below the 5th percentile (z-score<-1.64) should be considered pathological. Many studies involving the diagnosis, epidemiology or treatment of COPD have adopted the simple and practical GOLD spirometric criteria to define airway obstruction. Considering the age factors of patients diagnosed using a fixed ratio in studies on this subject, it has been observed that the disease can be missed in v individuals under 40 years of age, and that about 20% of individuals with advanced age are diagnosed with COPD even though they are not sick. International respiratory societies have called for further investigation of the differences between FEV1/FVC<0.7 and LLN-based definitions in predicting adverse health outcomes. In our study; We aimed to investigate the differences in predicting adverse health outcomes in COPD patients by comparing the exacerbation and mortality status of patients defined using the GOLD and GLI criteria. Our study was carried out by retrospectively examining the file records of 310 patients who were evaluated with the diagnosis and pre-diagnosis of COPD between 01/01/2019 and 30/06/2019 in Uludağ University Faculty of Medicine Hospital Chest Diseases Polyclinic. When the patients were defined according to the GOLD criteria, 71,6% were obstructive, 15,8% restrictive change and 26% were defined as normal, when defined according to the GLI criteria 57,4% obstructive, 20,3% restrictive change and 22,3% were defined as normal. They were divided into 3 groups as FR+/LLN+, FR-/LLN- and FR+/LLN- according to FEV1/FVC and LLN cut-off points. When the frequency of exacerbations was compared between the groups, it was observed that all exacerbations occurred most frequently in FR+/LLN+ patients, and the frequency of exacerbations requiring corticosteroid treatment and hospitalization increased in the FR+/LLN- group. In the analysis performed after the factors affecting exacerbations were corrected, a significant increase in risk was observed in the FR+/LLN+ and FR+/LLN- groups, and the patients with the highest risk increase were those defined as FR+/LLN-. When the groups were compared in terms of mortality, no significant difference was observed between them in terms of mortality frequency and risk. Keywords: COPD, airway obstruction, LLN, mortality, exacerbation