What Causes a High Bun?

Are you concerned because you had an elevated BUN level on a routine lab test? Find out what this means and whether it’s cause for concern.

Have you had blood work checked recently and been told you have an elevated BUN? You may be wondering what this test means and whether you should be concerned about an elevated level. BUN or blood urea nitrogen is a component found in the blood that’s routinely measured when your doctor checks a chemistry panel as part of your physical exam.

A High Bun Level: What Does It Mean?

The liver produces urea as a waste product when protein is metabolized. Normally, most of this urea is removed from the bloodstream by the kidneys. When the kidneys aren’t functioning as well as they should urea can build up in the blood causing an elevated BUN level. Checking BUN and another component called creatinine gives some indication as to how well the kidneys are functioning. When BUN and creatinine are both elevated on a blood test it can be the first indication of a kidney problem.

Is It Always Due to Kidney Problems?

Fortunately, a high BUN level doesn’t always indicate kidney disease. There are other reasons why blood urea nitrogen can be elevated on a lab test. One of the most common is simple dehydration, or not drinking enough fluid. If the BUN is elevated from dehydration, usually the creatinine, the other measure of kidney function, will be normal or even low on the same test. Many doctors look at something called the BUN to creatinine ratio to see if dehydration is the cause of an elevated BUN. If the BUN to creatinine ratio is high, it usually indicates dehydration. Other conditions that can cause a high BUN to creatinine ratio are kidney stones or bleeding from the digestive tract such as from a bleeding ulcer.

If lab studies show that you have a high BUN level and an elevated creatinine level, your doctor will probably do further testing since this indicate that the kidneys aren’t functioning as well as they should. This can be due to kidney disease related to diabetes or hypertension or can be caused by another condition such as an autoimmune disease that’s affecting the kidneys. If both of these values are high, it’s important to find out why.

Other Reasons for a High BUN

Other causes of a high BUN level? Some medications can cause an elevated BUN level including some antibiotics, anti-inflammatory medications, and gout medications. There are too many to list here, so it’s important to check with your doctor to find out if your prescrioption could be causing an elevation in BUN level. In rare cases, a high BUN can be caused by a heart attack or heart failure, although you’ll usually have other heart related symptoms if this is the cause. In some cases, eating a high protein diet can cause a high BUN level since urea comes from the breakdown of protein.

The Bottom Line?

Since the most likely cause of an elevated BUN when the BUN to creatinine ratio is normal is dehydration, your doctor may want to repeat your labs after you’re better hydrated, particularly if the BUN was only mildly elevated. If you’re otherwise healthy with a normal creatinine, a high BUN may be nothing to worry about, but always follow up with your doctor to find out why.

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  1. Nice info.

  2. Hi Kristie,
    Recently I have noticed that my daughter’s urine smells more like BM than urine. I have her scheduled to see her doc on Monday. I wonder if her BUN level is too high.
    Thanks again for the helpful information. I hope you enjoy your Thanksgiving Day.

  3. Very informative. Thanks for sharing.

  4. very informative..loads of unknown info..thanks

  5. very good information, i’m sure it will be useful for many of us

  6. Excellent article, I have been researching this information lately, and your article came up.

  7. informative again..

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