“Blood Urea Nitrogen Level in Patients With Chronic Total Occlusion Predicts Long-Term Mortality Independent of Estimated Glomerular Filtration Rate and Serum Creatine Level: (9-Year Follow-up Results)”. Annals of Medical Research, vol. 28, no. 10, Oct. 2021, pp. 1801-6, http://annalsmedres.org/index.php/aomr/article/view/3930.