REN and chronic obstructive pulmonary disease: AIDS: Acquired immunodeficiency syndrome; CCI: Charlson Comorbidity Index; COPD: Chronic obstructive pulmonary disease; eGFR: Estimated glomerular filtration rate; HIV: Human immunodeficiency virus; IQR: Interquartile range; K+: Potassium; RAAS: Renin-angiotensin-aldosterone system; SD: Standard deviation