Chapter 16 Laboratory Assessment ● ● ● ● ●

cholinergic agents anticoagulants digitalis

erythromycin isoniazid

● methyldopa Blood Urea Nitrogen

Normal Values ●

● ●

Adults: 10 to 20 mg/dL; 3.6 to 7.1 mmol/L (SI) (5)

Older adults: slightly higher than for adults (5) Nutritional Significance

The BUN level is directly related to the metabolic function of the liver and excretory function of the kidney. BUN increases as the kidney’s function declines. Slightly higher values of BUN seen in older adults are often the result of an inability to concen- trate urine or dehydration. If the BUN continues to increase, it may indicate that the kidney function is declining. The BUN is interpreted in conjunction with the creatinine test to assess kidney excretory function. A BUN greater than 100 mg/dL usually indicates serious kidney problems (1,2,5).

The BUN also increases in individuals on a high-protein diet or who have gastrointestinal (GI) bleeding. Both result in excess amounts of protein in the hepatic circulation, which lead to elevated BUN levels. Dehydration also creates a temporary elevation of BUN, so BUN is often used as a measure of hydra- tion status after surgery (1,2,5).

In clients with both kidney disease and liver disease, the BUN may be elevated and may then return to normal. This is not a reflection of improved renal excretory function but rather an indication that the liver is unable to form urea. As the liver continues to decline, the blood ammonia levels will rise, while the BUN may remain normal or slightly elevated (1,2,5).

●

BUN levels increase with (1,2,5): increased protein catabolism hemorrhage into GI tract acute MI stress

➤ ➤ ➤ ➤ ➤ ➤ ➤ ●

starvation diabetes fever burns

impaired renal function ● ● ● ● ●

congestive heart failure (CHF) urinary obstruction dehydration

very-high-protein diet BUN levels decrease with:

● severe liver damage drugs

➤ ➤ ➤

poisoning hepatitis

impaired absorption celiac disease

➤ ● ●

low-protein, high-carbohydrate diet overhydration

● ● ● ● ● ● ●

The following drugs may increase BUN levels: allopurinol

aminoglycosides cephalosporins furosemide guanethidine indomethacin methotrexate

● methyldopa aspirin

● ● ● bacitracin carbamazepine

● neomycin ●

● ● ● ●

penicillamine propranolol

spironolactone tetracyclines rifampin

The following drugs may decrease BUN levels (1,2,5): ●

●

chloramphenicol streptomycin

Creatinine

Normal Values ●

● Men: 0.6 to 1.2 mg/dL; 53 to 106 μmol/L (SI) (5)

Women: 0.5 to 1.1 mg/dL; 44 to 97 μmol/L (SI) (5)

Older adults: slightly decreased (5)

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