Two laboratory blood tests that measure kidney function are creatinine and blood urea nitrogen, or BUN. Both tests are related and are associated with the complete metabolic profile, or CMP. Either test can be run on a blood sample or urine sample. Abnormal levels indicate a kidney- or liver-related disease or condition.
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Abnormal Blood Creatinine
Abnormal levels of creatinine are found in conditions and diseases affecting the kidneys. The creatinine level measures kidney function and is often elevated when damage to the kidneys or blood vessels of the kidneys occurs. Autoimmune diseases can cause the blood vessels to swell. Urinary infections, especially in the kidney, will cause abnormal creatinine levels.
Elevated levels are also found in kidney destruction or necrosis. Patients with little or no kidney function will have very high blood levels of creatinine. Artificial kidneys are used in a process called dialysis to filter out toxic levels.
Low levels of creatinine are found in conditions that cause decreased muscle mass. Decreased levels are temporarily found in pregnancy as well.
Abnormal BUN Levels
Many diseases that affect the kidney or liver can cause the BUN level to be elevated or decreased. Simple dehydration can cause an elevated BUN level. The BUN level is primarily used to monitor kidney function or to obtain a baseline before certain drug therapies are started.
Diseases and conditions that result in an elevated abnormal blood urea nitrogen level can include high-protein diets, high blood pressure, chronic diseases, diabetes, heart failure and heart attack. The kidneys filter the body’s entire blood supply, so everything that affects the blood also affects the kidneys which, in turn, affects the BUN level.
Decreased levels of BUN can indicate liver failure and malnutrition. Vegetarians may have a low BUN, but a low level is considered normal in vegans.
The BUN/Creatinine Ratio
Doctors will look at the ratio between a person’s BUN and blood creatinine to help them determine what is causing the concentrations to be higher than normal. The reference ranges for each test as well as the ratio between the two tests are posted along with the test results. The reference ranges tell the doctor whether or not the result is normal or abnormal.
An increased ratio of BUN to creatinine may be due to conditions that cause a decrease in the flow of blood to the kidneys, such as congestive heart failure or dehydration. It may also be seen with high protein blood levels or from gastrointestinal bleeding.
A decreased ratio may be observed with liver disease and poor diet. Temporary levels that are high or low may not be a cause for concern and should be retested to confirm.
Dialysis is used to filter the blood when the kidneys are not functioning properly. Kidney failure can be acute and sudden. According to the Mayo Clinic, acute kidney failure is often seen in hospitalized patients, especially those requiring intensive medical care. Failure typically occurs following serious injury, when blood flow to the kidneys is impeded, and after complex surgical procedures. It is possible to correct the underlying cause of kidney failure and reverse it with temporary dialysis.
Chronic Abnormal BUN and Creatinine Levels
The loss of kidney function is a chronic condition that must be treated with dialysis on an ongoing basis. The BUN and creatinine measurements are good ways to monitor renal failure. A successful kidney transplant is the only way to recover and get off of dialysis.