BUN/Creatinine Ratio: This test compares two waste products in your blood — BUN (Blood Urea Nitrogen) and creatinine — to help check how well your kidneys are working. BUN comes from protein breakdown. Creatinine comes from muscle activity. The BUN/Creatinine ratio can help find out the cause of kidney problems or dehydration: A high ratio may suggest dehydration, heart problems, or high protein intake. A low ratio might be seen in liver disease or malnutrition.