Hypertension Blog

Serum creatinine and blood urea nitrogen (BUN) tests can help detect kidney damage resulting from hypertension. The increased systemic vascular resistance caused by hypertension promotes renal vascular changes and decreases renal blood flow. Diminished blood flow through the glomeruli triggers the release of renin, further increasing vasoconstriction and systemic vascular resistance. The glomeruli atrophy, and the kidneys shrink, inhibiting the excretion of creatinine and BUN.

Normally, the kidneys excrete creatinine-a waste product of muscle metabolism. Usually, serum creatinine levels range from 0.8 to 1.2 mg/dl in men and from 0.6 to 0.9 mg/dl in women. But when reduced blood flow through the glomeruli hinders renal excretion, serum creatinine levels are elevated.

The kidneys also filter and excrete the nitrogen fraction of urea-a waste product of protein metabolism. Normal BUN levels range from 8 to 26 mg/dl.

Test Implications

Elevated BUN levels alone don’t indicate renal dysfunction because infection, trauma, GI bleeding, diet, and dehydration can also increase BUN levels. But when a patient has elevated BUN and serum creatinine levels, he probably has reduced glomerular blood flow and kidney dysfunction.

If a patient is taking a diuretic or an ACE inhibitor to treat his hypertension, closely monitor his BUN and creatinine test results. Diuretics generally increase water and sodium excretion, which lowers circulating intravascular volume. As circulating volume decreases, so does renal blood flow, causing a rise in BUN and creatinine levels.

Other drugs can also influence a patient’s test results. For example, aminoglycosides can increase creatinine levels. Drugs such as allopurinol, furosemide, and indomethacin can increase BUN levels. And chloramphenicol can decrease BUN levels.

Changes in the patient’s protein intake and overhydration and underhydration can also affect the test results