Urea,
an end product of protein metabolism, is excreted by the kidney. BUN is
directly related to protein intake and nitrogen metabolism and inversely
related to the rate of excretion of urea. Urea concentration in glomerular
filtrate is the same as in plasma, but its tubular reabsorption is inversely
related to the rate of urine formation.
Normal
Range: 8-20 mg/dL
increased
in: Renal failure (acute or chronic), urinary tract obstruction, dehydration,
shock, burns, CHF, gastrointestinal bleeding. Drugs with renal toxicity,
eg, gentamicin.
Decreased in: Hepatic
failure, nephrotic syndrome, cachexia (low-protein and high-carbohydrate
diets).
Additional: Urease
assay method commonly used. BUN/Cr ratio (normally 12:1-20:1) decreased
in acute tubular necrosis, advanced liver disease, low protein intake,
following hemodialysis. BUN/Cr ratio increased in dehydration, GI bleeding,
increased catabolism.
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