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BUN or Urea

The Foundation for IgA Nephropathy

BUN or Urea

BUN stands for blood urea nitrogen. It measures the amount of a waste product called urea in the blood. Urea is formed by the liver in the process of ridding the body of ammonia which is built up as protein you eat is broken down. It is normally excreted in the urine. If kidney function is impaired, the urea builds up in the blood. In general, the higher the urea the worse the kidneys are functioning. However, the BUN can also rise because of other reasons, even if the kidney function is still good. People in Canada, Europe and other parts of the world may not actually find BUN or the term "blood urea nitrogen" printed anywhere on their lab reports. In this case, the test is simply called "urea", and the lab results are given in SI units, as in the table below.

Reference Ranges:
mg/dL (Urea-N)
(used in the U.S.A.)
SI Units (mmol/L) (Urea)
(Canada, Europe, etc.)
<1 yr
1-13 yr
14 yr +

Common causes of Higher Values (other than the renal failure):
Eating unusually-high protein foods
Bleeding in the upper gastro-intestinal system
High stress on the body, such as from a high fever
Dehydration (this is the most common cause)

Signs and Symptoms associated with high levels:
It's important to realize that urea itself is not very toxic. Like creatinine, it's simply a marker of possible reduced kidney function. However, elevated urea levels can have some effects such as:

dry and/or itchy skin
urine-like body odor and/or breath
taste and smell (senses) could be affected

Common causes of Low Values
very low protein intake
other conditions which prevent protein from becoming available to the body (such as celiac disease, losing too much protein in the urine)
Overhydration (such as when drinking too much water, which kidney patients sometimes do mistakenly thinking it will "help their kidneys)

Should I worry if my BUN or Urea is high?
Urea is something that needs to be interpreted in context by your nephrologist. Since you know you have kidney disease, you should not be unduly concerned about it, because it will be elevated if you have chronic renal insufficiency. Of course, large changes from one test to the next need to be evaluated by your doctor. It will get higher as renal failure becomes more advanced, and it may be a factor, among others, in deciding when it's time to start dialysis. However, chances are that you will see it go up and down many times during the years you have IgAN because of diet and hydration.

© 2002-2006 Foundation for IgA Nephropathy

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