Physicians normally recommend a blood urea nitrogen, or BUN, test along with creatinine levels to evaluate and measure how your kidneys are functioning. Laboratories often test BUN and creatinine levels together or in a group of blood tests known as a basic or complete metabolic panel, which also tests electrolyte function. This can often allow physicians to get a better overall picture of how the kidneys are eliminating wastes and at what rate.
Function
Physicians most commonly test BUN and creatinine to diagnose kidney disease or to monitor patients with acute or chronic renal failure. Lab Tests Online explains that your physician will often order these tests if he notes signs and symptoms of kidney dysfunction such as mid-back pain, high blood pressure, fatigue, poor appetite, swelling and puffiness especially in the face or ankles or urine that is foamy, coffee-colored or bloody. It may also help evaluate a person's general well being during a routine physical or during a hospital stay. In some cases, physicians will run a BUN and creatinine level before starting a drug therapy to ensure the kidneys can properly remove wastes.
BUN
Urea nitrogen is a substance that forms when proteins break down. A normal BUN level is between 7.0 and 20 milligrams per deciliter, or mg/dL, though these numbers can vary by laboratory, according to the National Institutes of Health. A normal BUN level indicates that the body is able to properly break down and rid itself of excess proteins. An elevated BUN level alone does not always indicate a kidney disorder.
Creatinine
Creatinine occurs when creatine, a part of your muscles, breaks down. A creatinine test measures how well the kidneys are filtering the small particles of creatinine from your blood. Your kidneys should remove all creatinine from the body. The National Institutes of Health explains that a normal value of creatinine is approximately 0.8 to 1.4 mg/dL, dependent upon the laboratory. Females normally have a lower creatinine level than men due to decreased muscle mass. A normal creatinine level indicates that your kidneys are able to properly remove all creatinine.
Abnormal Results
Elevated BUN levels may indicate acute or chronic kidney disease, damage or failure, according to Lab Tests Online. In some cases, the kidney damage is due to an underlying condition such as congestive heart failure, stress, shock, severe burns, heart attack or dehydration. Low BUN levels are uncommon but can occur due to malnutrition and liver disease.
Elevated creatinine levels can indicate damage to the kidney's blood vessels due to infection or autoimmune dysfunction, a bacterial infection in the kidneys, death to the tubules of the kidneys or prostate problems. It can often indicate reduced blood flow to the kidneys due to dehydration, shock, diabetes, atherosclerosis or congestive heart failure. Lab Tests Online indicates that low creatinine levels are rare and usually not cause for concern.
Considerations
People who have a diet high in protein will often have an elevated BUN and people with a low protein diet will have an abnormally low BUN, though this is not common. Women may also notice fluctuations of BUN and creatinine levels when pregnant, according to Lab Tests Online.
