Ilyas, M., Agussalim, A., Megawati, M., Massi, N., Djaharuddin, I., Bakri, S., As’ad, S., Arief, M., Bahar, B., Seweng, A. and Prihantono, P. (2019) “Relationship between Vitamin D Level and Serum TNF-α Concentration on the Severity of Chronic Obstructive Pulmonary Disease: Vitamin D Level and Serum TNF-α related to the Severity of Chronic Obstructive Pulmonary Disease”, Open Access Macedonian Journal of Medical Sciences, 7(14), pp. 2298–2304. doi: 10.3889/oamjms.2019.663.