BUN (Blood Urea Nitrogen) Test

This test measures urea nitrogen (BUN) in serum. Urea is the principal waste product of protein breakdown, made in the liver and cleared by the kidneys. On its own it does not report eGFR; for an estimate of kidney filtering, pair it with the creatinine test, which includes eGFR. Clinicians also compare BUN with creatinine (the BUN-to-creatinine ratio) to help find the cause of a kidney problem, which needs both values.

People checking or monitoring kidney function, especially with diabetes, high blood pressure, heart disease, obesity, a family history of kidney problems, age over 60 or smoking; people who want to re-check a BUN that came back high or low on a previous panel; and people whose clinician follows hydration or kidney effects of medicines.

Any time of day; no fasting is needed. Because hydration and recent protein intake both move BUN, testing under your usual conditions (normal fluids, normal diet) gives the most representative result and makes repeat tests comparable.

Quest's adult reference range for this code (age 20 and over) is 7-25 mg/dL; your report shows the range that applies to you. A high BUN can reflect reduced kidney function, dehydration, reduced blood flow to the kidneys (for example heart failure), a high-protein diet, burns, fever or severe infection, a recent heart attack, some medicines, or a blockage in the urinary tract. A low BUN is less common and can reflect a low-protein diet, malnutrition, advanced liver disease or overhydration. An abnormal BUN does not by itself mean you have a condition needing treatment; clinicians interpret it with creatinine and eGFR and often repeat it. JustLabs results are informational; review them with a clinician.