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Kidney Diseases

BUN:creatinine ratio

10/23/2007

Question:

Do I have to worry about a creatinine level of 0.6 and bun:creatinine ratio of 35? As far as I know I am in good health. This result was after a 12 hr fast with other tests which were normal. I ate pasta and beans the night before and a small porkchop, some cheese and cooked greens. Urea level was 21. Urinalysis was unremarkable.

Answer:

I do not see any cause for worry here.

BUN (blood urea nitrogen) and creatinine are waste products that are produced by normal metabolic processes in the body and by the breakdown of foods, especially those high in protein.  The normal value for BUN is approximately 10-20, and for creatinine, 0.5-1.2.  BUN and creatinine are normally excreted by the kidneys, so they accumulate in the bloodstream when a person has kidney failure.  Therefore, with renal disease, the BUN and creatinine usually both rise together.  However, there are some conditions in which one rises more than the other, and some (as in yours) where the BUN is at the high end of normal while the creatinine is at the low end of normal.  Here are some possible explanations:

1) Are you a small person, or are you pregnant?  This could make the creatinine level be low. 

2) Mild dehydration: after a 12-hour fast, your body may have been a little water-depleted, which could cause the BUN to be on the high side but would not affect the creatinine much, if at all (resulting in a high ratio).

3) Heart failure or liver cirrhosis: both of these conditions can cause a high BUN/creat ratio in the absence of kidney problems.

4) Very high protein diet: a high protein diet (in general, not just on the night before the test) may increase the BUN without affecting creatinine, so that the ratio may become elevated. 

5) GI bleeding: if there is a bleeding ulcer or bleeding of any type anywhere in the stomach or intestines, the BUN will rise disproportionately from the creatinine. 

6) Steroids: in people taking high doses of steroid medications such as prednisone, the BUN can be elevated, causing a high calculated BUN/creatinine ratio.

In any case, it does not sound like you have kidney disease of any kind.  Perhaps one of the other explanations above fits; but if not, I would not worry any more about this.

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Response by:

Mildred   Lam, MD Mildred Lam, MD
Associate Professor of Medicine
School of Medicine
Case Western Reserve University