The bun-to-creatinine ratio is a standard medical test that measures the ratio of two substances in the blood, blood urea nitrogen (BUN) and creatinine. They are waste products that are filtered out by the kidneys, and the ratio can help determine how well the kidneys are working. The test is also known as B/C ratio or urea-to-creatinine ratio. Other synonyms for this test include renal function test and kidney function test. The test is commonly used in diagnosing kidney diseases, dehydration, and other conditions that affect kidney function. It is important to discuss the results of this test with a healthcare provider to determine the best course of treatment.