IJSR International Journal of Scientific Research 2277 - 8179 Indian Society for Health and Advanced Research ijsr-11-2-40690 Original Research Paper Study on vitamin D3 level and C reactive protein titre among patients with chronic obstructive pulmonary disease and their association with disease severity. Surajit Chatterjee Dr. Dr Rituparna Bose Dr. February 2022 11 2 01 02