Baig A, Siddiq S, Butt MR, Salik S. Association of Serum Vitamin D Levels in Acute Exacerbation of COPD. IJBR [Internet]. 2025 May 30 [cited 2026 May 31];3(5):1010-4. Available from: https://ijbr.com.pk/IJBR/article/view/2209