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Urea is a waste product, formed in
the liver and excreted in the urine at a relatively constant rate.
BUN (blood urea nitrogen) is a measurement of the nitrogen part of
urea, and is therefore an indirect measurement of the urea in the
bloodstream.
Elevations caused by:
- Kidney malfunction, as is seen in glomerulonephritis, pyelonephritis,
and shock.
- Increased metabolism of proteins, as is seen with GI bleeding, a
high protein meal, heart attack, diabetes, or infection.
- Dehydration and hemoconcentration
- Crush injuries
Decreases caused by:
- Liver failure
- Normal Pregnancy
- Excessive hydration
Note:
- BUN is a fast way to evaluate kidney function, but has some
limitations.
- Small changes in BUN may occur from medications, dietary changes and
hydration status and have little significance.
- Big changes in BUN occur only in fairly extreme circumstances.
- A more sensitive (but more complex) test of kidney function is the
creatinine clearance.
- With an elevated BUN, one way to distinguish between renal disease
and increased production of urea (such as is seen in GI bleeding) is
the BUN/creatinine ratio. It increases with increased metabolism, and
decreases with renal disease.
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Normal Values:*
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mg/dL |
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Adults |
8-23 |
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Children |
5-15 |
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Pregnancy |
5-12 |
*These are general values taken from a variety of
sources. The actual normal values may vary from lab to lab and from one
type of testing protocol to another.
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Source:
Operational Medicine 2001, Health
Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau
of Medicine and Surgery, Department
of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300
OB-GYN 101:
Introductory Obstetrics & Gynecology
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Brookside Associates, LLC
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