Blood urea nitrogen: A measure of the urea level in blood. Abbreviated BUN. Diseases that compromise the function of the kidney frequently lead to increased BUN levels. From Healthy Resources 10 Rheumatoid Arthritis SymptomsWhat Is Exocrine Pancreatic Insufficiency?Understanding COVID-19 Testing and Treatment Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors