H–23
Chemistry Description and Guide
Urea/UREA/BUN
The catabolism of proteins results in the production of ammonia which is extremely
toxic. This is converted to urea in the liver and eliminated from the body by glomerular
filtration in the kidneys.
Principal reason for performing the test:
As an indicator of renal disease.
Most common abnormality indicated by the test:
Renal disease
Special precautions in sample collection:
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sodium fluoride or EDTA as anticoagulants. Samples that contain hemoglobin increase
urea nitrogen.
Important: For optimum performance, NH
3
testing should not be performed when
any UREA/BUN slides are in the same run.
Complementary tests:
Urea concentration should usually be determined in conjunction with measurements
of creatinine, inorganic phosphate, total protein, and albumin. Urea concentration is
considered to be more influenced by high protein diet than creatinine. A PCV can be
helpful as an indicator of reduced erythropoietin production. Appropriate urine tests
should also be performed (e.g., specific gravity and protein concentration).
An increase in both serum urea and creatinine provides a more reliable index of renal
disease than an increase in only one of the parameters, especially if changes are small.
It is generally accepted that urea concentration increases before creatinine in renal
disease in humans. However the precise relationship between these tests in different
animal species remains to be determined. Until this is resolved it may be prudent to
perform both urea and creatinine determinations where early renal disease is suspected.
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