The typical adult range for the BUN-to-creatinine ratio is 1 unit of creatinine for every 10 to 20 units of blood-urea nitrogen, states Lab Tests Online. However, WebMD claims the levels are normal if the ratio falls between 6 and 25 units of blood-urea nitrogen per unit of creatinine.
A high BUN-to-creatinine ratio sometimes indicates kidney problems or bleeding in the respiratory or digestive tract, reports WebMD. A low ratio potentially indicates rhabdomyolysis, liver disease or a condition called syndrome of inappropriate antidiuretic hormone secretion. In addition to illness, factors such as medications used, pregnancy and diet potentially affect this test result, notes Lab Tests Online.