Waseem, Hafiz Muhammad, et al. “PLASMA SURFACTANT PROTEIN-A LEVELS IN HEALTHY SUBJECTS AND CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS”. Journal of Ayub Medical College Abbottabad, vol. 32, no. 1, Jan. 2020, pp. 3-8, https://jamc.ayubmed.edu.pk/index.php/jamc/article/view/6183.