According to the National Kidney Foundation, kidney disease is the ninth leading cause of death in the United States. It affects 15% of the U.S. population, or around 37 million people, making it a serious public health concern. What’s even more concerning is that most people living with kidney disease don’t even know they have it. In many cases, chronic kidney disease doesn’t cause any symptoms until it’s considered moderate or advanced. As a result, people with chronic kidney disease have an increased risk of diabetes, high blood pressure, and other complications.
This guide explains what the BUN test is, why it’s used, and what it involves. It also provides an overview of CKD symptoms, risk factors, and treatment options.
The purpose of the BUN test is to determine if an individual has a higher-than-normal amount of urea nitrogen in their blood. In healthy people, the kidneys filter waste products out of the bloodstream, play a role in maintaining normal fluid volume, and help control blood pressure and other functions. When the kidneys are damaged, they can’t carry out these important functions as well as usual. As a result, urea nitrogen and other waste products build up in the blood, causing symptoms such as fatigue and nausea.
The BUN test is typically performed as part of a basic or comprehensive metabolic panel. In adults, both tests are often ordered once per year. The BUN test should also be done when an individual is experiencing symptoms of late-stage kidney disease. These symptoms include fatigue, muscle cramps, and frequent urination. People who have high blood pressure or diabetes should have this test, along with other kidney-function tests, at least once per year, as recommended by the American Academy of Family Physicians.
All that’s required for the BUN test is a blood sample.
No special preparation is required for the BUN test, but it may be necessary to fast for 10 to 12 hours if the test is to be performed as part of a basic or comprehensive metabolic panel. Both panels check the amount of glucose in the blood, which is affected by eating and drinking.
In people with chronic kidney disease (CKD), the kidneys have lost some of their ability to filter the blood. This allows minerals, fluid, and waste products to build up in the bloodstream. Sodium, potassium, calcium, and phosphorus are some of the most important minerals in the human body. Although they’re necessary for survival, allowing them to build up in the bloodstream can cause life-threatening complications.
In addition to filtering blood, the kidneys are also responsible for producing certain hormones, maintaining normal blood pressure, and inducing the manufacturing of blood cells. When kidney function is impaired, the kidneys can’t carry out these functions, increasing the risk for high blood pressure and medical problems caused by hormone imbalances or a lack of red blood cells. For example, some people with chronic kidney disease develop anemia, which can cause fatigue, dizziness, pale skin, chest pain, difficulty breathing, weakness, and headaches. People with CKD may also develop bone disorders caused by an imbalance of phosphorus and calcium in the blood. These disorders don’t cause symptoms right away, but as they worsen, can cause pain in the bones and joints.
CKD may not cause any symptoms at first. As the disease worsens, swelling is usually one of the first symptoms to appear. Swelling occurs because the kidneys can’t filter excess fluid from the bloodstream. People with CKD may also experience itching, dry skin, chest pain, fatigue, changes in urination, sleep problems, vomiting, muscle cramps, loss of appetite, or headaches. Some people are more likely to develop CKD than others. High blood pressure and diabetes both increase the risk for CKD by damaging the blood vessels that supply the kidneys. People with heart disease or a family history of CKD are also more likely to develop the disease.
When a health care provider orders a BUN test, the patient must provide a blood sample. The sample is obtained via a procedure known as venipuncture, which involves puncturing a vein with a needle. Before performing this procedure, a phlebotomist examines the patient’s arms to identify a suitable vein. Once the vein has been located, the phlebotomist uses a tourniquet to stop some of the patient’s blood from returning to the heart. This causes the blood to collect in the vein, making it easier to draw a blood sample. After puncturing the vein with a needle, the phlebotomist uses a tube to collect enough blood for analysis.
When the sample arrives at the laboratory, a laboratory scientist uses a procedure known as LX20 modular chemistry to quantify the amount of urea nitrogen in the blood. A normal BUN level usually ranges from 6 to 20 mg/dL (milligrams per deciliter).
Chronic kidney disease is usually irreversible, but it’s possible to slow the progression of CKD with lifestyle changes and medications. Since CKD causes minerals to build up in the bloodstream, diet is extremely important for managing kidney disease. The National Institute of Diabetes and Digestive and Kidney Diseases recommends avoiding high-sodium foods and consuming no more than 2,300 mg of sodium per day. High levels of sodium are typically found in canned soups, frozen meals, snack foods, and other prepared foods. Consuming less sodium can help a person with CKD avoid high blood pressure or control hypertension once it has developed. In the advanced stages of kidney disease, it may be necessary to consume less protein, as protein is broken down into several waste products that build up in the bloodstream when the kidneys aren’t working well.
People with advanced kidney disease may also need to limit their intake of foods containing high levels of potassium and phosphorus. The human body needs both minerals for survival, but too much potassium or too much phosphorus in the bloodstream can be dangerous. High levels of phosphorus are found in dairy products, poultry, fish, red meat, oatmeal, nuts, and beans. Bananas, oranges, potatoes, dairy products, whole-wheat bread, beans, brown rice, and nuts are considered high in potassium.
Several types of medications are used to prevent CKD complications and protect the kidneys from further damage. Some people with CKD take medication to reduce their blood pressure, which can prevent damage to the blood vessels in the kidneys. Statins may be used to lower cholesterol, reducing the risk of cardiovascular complications of CKD. In people with CKD who also have a high risk of heart attack, aspirin and other blood thinners may be used to prevent heart attacks. Finally, some people with CKD take medicine to reduce the amount of uric acid in their blood. If too much uric acid builds up in the bloodstream, it can cause a painful condition known as gout.
When the kidneys stop working, it may be necessary to start hemodialysis or receive a kidney transplant. Hemodialysis, commonly shortened to dialysis, is a process in which blood is removed from the body, filtered by a machine, and then returned to the individual’s bloodstream. The filtering process removes excess fluid and waste products from the blood, which can relieve some of the symptoms of CKD. Hemodialysis also helps control the individual’s blood pressure and prevent the complications that can occur when too much sodium, calcium, and potassium build up in the bloodstream.
Kidney transplantation involves taking a kidney from a donor and implanting it in a person with chronic kidney disease. Not everyone with kidney disease qualifies for a kidney transplant, so it’s important to work closely with a nephrologist (kidney specialist) to determine if transplantation is a viable option. The donor kidney can come from a living or deceased donor. If the organ comes from a deceased donor, the recipient must go to the hospital immediately after being notified that a kidney is available, as there’s a limit on how much time can pass between when the donor dies and when the kidney is transplanted into the recipient.
Not necessarily. A high BUN level can be caused by several conditions other than CKD. These conditions include heart attack, dehydration, urinary tract infections, gastrointestinal bleeding, and congestive heart failure. If a single test shows an elevated BUN level, more tests are usually needed to determine the underlying cause.
Not necessarily. It’s possible to have kidney disease and still have a normal BUN level. In addition to the BUN test, a health care provider may order a creatinine test, a urine protein test, a microalbuminuria test, or a GFR test to determine if the kidneys are functioning normally. Like urea nitrogen, creatinine is a waste product that forms during protein metabolism. It’s possible to have a normal BUN level and a high creatinine level, indicating that the kidneys aren’t working at their full capacity. The urine protein test is used to determine how much protein is in an individual’s urine. A high urine protein level is an indicator of kidney damage.
The microalbuminuria test is more sensitive than the protein test, as it detects small quantities of protein in an individual’s urine. The results of this test can be used to gauge the amount of damage that has been sustained by the kidneys. GFR stands for glomerular filtration rate and is a measure of how well the kidneys are working. In healthy adults, a normal GFR is 90 or above. A GFR of 60 to 89 may be normal in some people, but a GFR below 60 is abnormal. Anyone with a GFR below 30 should see a kidney specialist regularly. A GFR below 15 indicates that an individual is in kidney failure and may need hemodialysis or a kidney transplant.
It depends on how much urea nitrogen is in the blood and whether other test results are abnormal. Not everyone with an elevated BUN level needs treatment right away. A healthcare provider may decide to order the test again in a few months to see if the individual’s BUN level is still high.
A high BUN level is usually anything over 20 mg/dL, however, some laboratories have different reference ranges. It’s important to discuss the results with a medical professional to determine what’s normal for a particular lab.
Yes. People who follow a high-protein diet may have higher levels of urea nitrogen in their blood. Certain medications may also cause elevated BUN levels. These medications include high-dose aspirin, diuretics, some antibiotics, and some drugs used to treat high blood pressure. People with severe burns may also have higher-than-normal amounts of urea nitrogen in their blood.
With venipuncture, there is a slight risk of infection once the skin has been pierced with a needle. A phlebotomist will reduce the risk of infection by cleansing the skin thoroughly before inserting a needle. After a blood draw, some people experience bruising or mild tenderness at the insertion site. Dizziness and fainting may also occur during a blood draw. Anyone with a history of fainting during this procedure should alert the phlebotomist before having blood drawn for a BUN test.
|The Cleveland Clinic||my.clevelandclinic.org/health/articles/15641-renal-diet-basics||The Cleveland Clinic offers tips for following a renal diet, which is the diet recommended for people with chronic kidney disease.|
|MedlinePlus||www.medlineplus.gov/chronickidneydisease.html||MedlinePlus provides a detailed overview of chronic kidney disease and its symptoms.|
|NIDDK||www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/managing||The National Institute of Diabetes and Digestive and Kidney Disease explains how to keep kidney disease under control.|
|National Kidney Foundation||www.kidney.org/atoz/content/kidneytests||The National Kidney Foundation provides details on several blood tests and imaging tests used to diagnose kidney disease and monitor kidney function in people with CKD.|
|National Kidney Foundation||www.kidney.org/atoz/atozTopic_Transplantation||The National Kidney Foundation offers a list of resources aimed at preparing people with CKD to receive a kidney transplant and take care of their new kidneys once transplantation has occurred.|