In medical terminology, a BUN-to-creatinine ratio refers to the high or low ratio of blood urea nitrogen to creatinine, states Lab Tests Online. BUN-to-creatinine ratios are helpful for gauging the health of the kidneys and uncovering underlying, related health issues.
The kidneys filter BUN and creatinine from the blood and excrete them as urine, explains MedicineNet. When the kidneys function optimally, a person's BUN-to-creatinine levels typically hover within a specific range, 10:1 and 20:1, according to Lab Tests Online. Men tend to have higher BUN-to-creatinine ratios than women, states the Mayo Clinic.
While a high BUN-to-creatinine ratio may indicate impaired kidney function, BUN-to-creatinine ratios differ from person to person based upon age, race and body size, explains the National Kidney Foundation.
When the body metabolizes protein in the diet, the waste product is BUN. When the body breaks down protein that is already present in the body, such as muscle, the waste product is creatinine, states DaVita Kidney Care. Consequently, consuming large amounts of protein, not enough protein or inadequate amounts of water can upset the BUN-to-creatinine ratio, and so does strenuous exercise and muscle injuries.
Doctors order BUN tests and creatinine blood tests as part of a basic or metabolic panel, according to Lab Tests Online. A doctor may also order such tests if a patient complains of symptoms consistent with kidney failure, such as fatigue, midback pain, high blood pressure, coffee-colored urine or a burning sensation during urination.