Neutrophil to Lymphocyte Ratio in Acute Exacerbation of Chronic Obstructive Pulmonary Disease: A Marker of Severity and Prognosis

Chronic obstructive pulmonary disease (COPD) stands as one of the leading causes of mortality worldwide, posing an increasing economic burden. Acute exacerbations of COPD (AECOPD) are defined as acute deterioration of respiratory symptoms requiring additional treatment, leading to rapid respiratory function decline, diminished quality of life, and worsened disease status. Neutrophils are the most common type of white blood cells (WBC) and participate in multiple inflammatory and immune processes through phagocytosis and cytokine release. Lymphocytes play a crucial role as coordinators of the inflammatory and immune processes in various physiological mechanisms. The neutrophil-to-lymphocyte ratio (NLR) is calculated by dividing the number of neutrophils by the number of lymphocytes in the peripheral blood test, reflecting an increase in neutrophils and a secondary decrease in lymphocyte count during the inflammatory response. The NLR is considered a biological marker reflecting the inflammatory condition and is increasingly recognized in various disorders such as pneumonia, malignant, coronary artery disease, or hematological disorders.