A BUN (blood urea nitrogen) test is utilized to determine the functioning of your kidneys. It measures the levels of blood urea nitrogen. Urea nitrogen is a byproduct (waste product) of protein breakdown in the liver. Under normal conditions, urea nitrogen is filtered by the kidneys, which is then removed from the body in urine. BUN levels are raised when any damage is caused to liver or kidneys. Hence, normal blood urea nitrogen levels are of essential importance.
What Are Normal BUN Levels?
The range of normal levels of blood urea nitrogen is between 7 and 22 mg/dL. A result greater than 50 mg/dL indicates an underlying medical problem.
BUN levels also change with gender and age and during pregnancy. Generally, blood urea nitrogen levels increase with increasing age. BUN levels in toddlers are around 66% of the levels found in an average healthy adult. Levels in adults over age 60 are greater than levels in young adults.
BUN levels according to gender and age:
- Children: 5-18 mg/dL
- Adult male: 8-20 mg/dL
- Adult female: 6-20 mg/dL
What Causes Abnormal BUN Levels?
After discussing the normal BUN levels, let’s discuss the factors which raise and decrease the BUN levels.
Factors That Raise BUN Levels
- A diet high in protein
- Infection or fever, which increases the breakdown of proteins – a common feature of any illness
- Interval training or inflammation, which leads to breakdown of proteins from muscles
- Low consumption of water or dehydration. BUN levels are increased as blood volume is decreased.
- Stress. BUN is elevated when activation of sympathetic arginine-vasopressin and angiotensin-aldosterone systems is inappropriately increased. This is often seen in heart failure. Protein breakdown is also increased by cortisol hormone, thereby elevating BUN levels.
- Bleeding from the gut. When bleeding from upper GI tract occurs, that blood is digested to form protein. This protein is then metabolized to BUN by the liver.
- Poor circulation, which leads to decreased blood flow to the kidneys, thereby decreasing their ability to filter urea nitrogen
- Abnormalities of the thyroid gland, which leads to abnormal functioning of the kidneys
- Glucocorticoids, tetracyclines and other antianabolic drugs
- Kidney failure or disease and urinary tract blockage by a kidney stone
Factors That Decrease BUN Levels
- A diet low in protein, starvation or malnutrition
- Impaired activity of the liver due to disease of the liver
- Genetic deficiency of the enzymes of the urea cycle
- High levels of growth hormone. It inhibits the synthesis of urea. Growth hormone deficient children who receive human growth hormone have decreased levels of BUN.
- Anabolic steroids as they decrease the breakdown of proteins
- Drinking a lot of water or overhydration
- Pregnancy (the reason is increased plasma volume.)
How to Manage BUN levels
It is quite possible to get normal BUN levels after episodes of decreased or increased BUN levels. Keeping your BUN levels in the normal range depends on the underlying cause of the abnormal BUN levels and may require following appropriate lifestyle changes, taking prescribed medicines and eating a healthy and well-balanced diet.
- If the cause of your abnormal BUN levels is eating excessive protein, then you should avoid eating foods rich in protein such as fish, meat, dairy and beans and increase your intake of fruits and vegetables. You should stay hydrated by drinking plenty of water to keep your BUN levels in normal range.
- If the cause of your abnormal BUN levels is kidney disease, you may be prescribed certain medications to slow down the progression of your disease during early stages. If you have developed kidney failure, then you may require intensive treatment including dialysis.
- Levels of BUN have also been linked to the presence of high blood pressure and diseases that restrict the flow of blood such as diabetes. As blood pressure can be greatly impacted by stress, exercising regularly, seeking counseling and decreasing stress may help you maintain normal BUN levels. Keeping your blood sugar levels normal also helps in promoting healthy BUN levels.
BUN: Creatinine Ratio
The test to check BUN level is often done in association with creatinine test, especially if an underlying kidney disease is suspected. The normal range of BUN: creatinine ratio is in between 10:1 and 20:1. This ratio should not be more than 30:1 in infants younger than 1 year. Elderly individuals have a slightly higher ratio of BUN: creatinine in comparison to young, healthy adults. The value is slightly greater in males in comparison to females.
An increased BUN: creatinine ratio indicates acute kidney failure, dehydration, mental shock, congestive heart failure or decreased flow of blood to the kidneys. On the contrary, a decreased ratio indicates malnutrition, SIADH (syndrome of inappropriate antidiuretic hormone secretion), central nervous system diseases, cancer, muscle injuries such as rhabdomyolysis, liver diseases and bleeding in the respiratory or digestive tract.
Patients undergoing dialysis of the kidney have to regularly check creatinine and BUN levels. Kidney function can be reliably evaluated by this method.