Blood urea nitrogen (BUN) test – procedure and uses

What is the BUN test?

A blood urea nitrogen test, called a BUN test, is nothing but a measure of the quantity of urea nitrogen in your blood. It is a part of the blood test in which the urea nitrogen levels will only be specifically checked.  

This blood urea test is carried out to check the functioning of your kidney. Based on the blood urea nitrogen or BUN levels in your blood, doctors can identify if you have any kidney disease or not.  

Blood urea nitrogen is a waste material removed from your blood by the kidneys. For this, your kidneys need to function properly.  

What is blood urea nitrogen?

Your liver produces ammonia (NH3) as a by-product. Here ‘N’ stands for nitrogen, meaning ammonia contains nitrogen. This nitrogen combines with other elements such as oxygen, hydrogen and carbon to produce urea.

Urea is a waste product in your body that mixes with your bloodstream and travels to your kidneys. A pair of healthy kidneys filter out the waste materials from your blood and release them through urine.  So, your blood, at any time, contains some amount of blood urea nitrogen, which is normal because the production of urea and its filtration is a continuous process.  

But, if the level of blood urea nitrogen is high, it could indicate that your kidney is not performing the normal function.  

Why do you need a BUN test?

The blood urea test is done to check if your kidney functions well. Your doctor prescribes the test if you develop any kidney-related problems. Under the following circumstances, your doctor may prescribe the BUN test:

• If you have chronic kidney disease or related problems
• If you have other health conditions, including Hypertension and Diabetes, that may affect your kidneys
• To check the efficacy of dialysis when you have kidney malfunction
• To diagnose other conditions such as congestive heart failure, gastrointestinal bleeding, liver damage, etc.  

It is important to note that a high blood urea nitrogen level doesn’t solely conclude any of the above health conditions.  If your doctor’s main concern is the kidney, the creatinine levels will be checked. Creatinine is another waste product that gets filtered out by your kidneys.  

A high level of creatinine in your blood may indicate the ineffective functioning of your kidneys.

However, the swifter the medical attention, the easier it is to address the health problem in its early stage. If any of the below symptoms listed are felt, consult your doctor and convey the symptoms.

• Urine becomes foamy, bloody, brown or discoloured
• Pain when you urinate
• Swelling of arms, ankles, legs, abdomen, face or eyes
• Experiencing pain in the mid-back
• Legs become restless during sleep
• Feeling weary all the time

How do you prepare for a BUN test?

A blood urea test is almost like any other normal blood test. If your doctor’s intention is only to check the blood urea nitrogen levels in your blood, you can go for the test even after having a meal.  

However, if your doctor prescribes to test your blood for other purposes, you may need to fast before the test. In such scenarios, adhere to what your doctor says.  

In addition, if you are on any medication, make your doctor aware of it. Certain medications may alter the test results. Your doctor may ask you to pause on it for the time being.  

How is a BUN test performed?

The procedure of a blood urea nitrogen test is not a complicated one. Your doctor collects a sample of blood from you. The blood urea nitrogen test method involves the following steps:

• Mostly, the blood is drawn from your arm.
• A lab technician will clean the area to be punctured with an antiseptic.
• Then, they will put pressure on your arm to make your veins swell by tying an elastic band around.
• They will insert a sterilised needle and draw a tiny portion of blood from your vein.
• They collect the blood in a small vial or tube and send it for the test.
• You may feel a slight twinge in the punctured area, but it will go away in no time.
• After all, these are over, you can walk out.  
• You will get the test results in a day or two.  

Things to do after bun test

Eat fresh fruits and vegetables every day 

People should intake fruits and vegetables if they have abnormal BUN levels. Drinking plenty of water also prevents BUN accumulation.

Eat foods low in salt 

Lower blood pressure and a lower risk of heart attack were observed in those who consumed less than 10 grams of salt per day. This also halts the production of urea nitrogen in the blood.

Do not smoke or use tobacco 

Smoking tobacco affects the arteries in the heart, resulting in plaque buildup and the formation of blood clots. Therefore, abstain from harmful substances like tobacco and alcohol.

Talk to your doctor about medicines 

BUN levels enable your doctor to assess how effectively your kidneys are functioning. The test may be done in conjunction with other measurements to aid in diagnosing a kidney condition or determine how well your kidney disease medication works.

Things that affect the test results 

A high-protein diet 

Higher quantities of urea and other nitrogen waste products may result from a high protein diet. Indeed, multiple research studies have shown a link between higher dietary protein intake and higher BUN concentrations.

Steroid use 

People who are about to take the BUN test must refrain from using steroid and anabolic drugs. This alters the original BUN levels and may show wrong BUN levels.

Dehydration 

BUN levels typically increase higher creatinine levels as a result of dehydration. BUN and creatinine levels increase when you have renal disease or an obstruction in the urine flow from your kidney. Before getting a blood urea nitrogen (BUN) test, avoid eating any high protein foods.

Ageing 

Regardless of age, male BUN levels are consistently and considerably more significant than female BUN levels. BUN value is seen as high in people, especially the elderly between the ages of 70-85.

What does the result mean?

The test results are mentioned in numbers. They indicate the blood urea nitrogen level in your blood that is measured in milligrams per deciliter (mg/dL). A normal range of blood urea nitrogen is as follows:

• For adult men: 8 to 24 mg/dL
• For adult women: 6 to 21 mg/dL
• For children (up to 17 years old): 7 to 20 mg/dL

The numbers for the normal range of blood urea nitrogen may vary slightly. In addition, several factors influence the test results.

For instance, having a high-protein diet can cause high blood urea nitrogen levels. Similarly, consuming a low-protein diet can cause low blood urea nitrogen levels.

Apart from these, the intake of some medications, especially steroids, highly influences the test results. Ageing and pregnancy also play a significant role in determining your BUN levels.  

What do the BUN levels mean?

As the fundamental motive of a BUN test is to check whether your kidneys are working properly, a high BUN level indicates that you may have developed some kidney problems.  

But it is not a conclusive test, as the high levels do not always mean that you have kidney disease. A high blood urea nitrogen level also means:

• Urinary tract obstruction
• Dehydration
• Congestive heart failure
• Stress
• Heart attack
• Gastrointestinal bleeding

Although people rarely develop low blood urea nitrogen levels, it is not uncommon. It may indicate:

• Malnutrition
• Liver disease
• Overhydration

Possible results from BUN Test

BUN test indicates the presence of the following conditions.

Kidney damage 

A specific BUN measurement cannot identify kidney failure. The BUN-to-creatinine ratio (BUN: Creatinine), which is more precise than the BUN test alone, can be determined by combining the BUN and creatinine tests.

Shock 

A specific BUN measurement cannot identify kidney failure. The BUN-to-creatinine ratio is more precise than the BUN test.

Urinary tract obstruction 

A high BUN level typically indicates that your kidneys aren’t functioning properly. However, increased BUN can also be due to urinary tract obstruction and sometimes due to dehydration.

Stress 

BUN is frequently elevated in heart failure due to an improper rise in the sympathetic, renin-angiotensin-aldosterone and vasopressin systems’ activity.

Heart attack 

A higher risk of heart disease is caused due to persistently elevated BUN levels. BUN levels while in the hospital may impact long-term clinical results.

Is the BUN test a conclusive one?

The blood urea test is an effective mechanism to check the conditions of your kidneys, yet it is not a conclusive one. So, doctors also prefer creatinine tests, for that matter.  

The BUN levels are compared with your creatinine levels in the BUN to creatinine ratio for assessing your kidney’s performance. The normal range usually falls between 10-to-1 and 20-to-1.  

Similar to the BUN test, a higher value indicates that you may have some kidney-related problems or other conditions such as congestive heart failure or gastrointestinal bleeding.  

A lower level indicates that you may be undernourished or have liver disease.  

To sum up

A BUN test is a simple procedure that checks the blood urea nitrogen levels. If your BUN level surpasses the normal blood urea nitrogen range, it may be a sign that your kidney is not functioning well.

However, it is not a conclusive test. Your doctor will diagnose your kidney-related problems by combining the BUN test with other tests and diagnoses.

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