Blood WorkBUN (blood urea nitrogen) measures urea, a waste product your liver makes from protein and your kidneys clear. It's part of a comprehensive metabolic panel (CMP), and the typical range is about 6 to 20 mg/dL. High BUN most often means dehydration, a high-protein diet or reduced kidney function; low BUN is usually harmless and can reflect low protein intake. BUN is read with creatinine and eGFR.
What does BUN measure?
When your body breaks down protein, your liver turns the leftover nitrogen into urea, and your kidneys filter it into urine. BUN shows how much urea is in your blood. It's a rough kidney check, but it also changes with how much protein you eat and how much fluid you drink, so clinicians rely more on creatinine and eGFR for kidney function.
What is a normal BUN?
| Result | What it usually means |
|---|---|
| Below about 6 mg/dL | Low: usually low protein intake, a lot of fluid, pregnancy, or less often liver disease. |
| About 6 to 20 mg/dL | Typical adult range. It runs a little higher in older adults. |
| Above about 20 mg/dL | High: dehydration, high protein intake, reduced kidney function, or other causes below. |
Your lab's printed range applies.
What causes high BUN?
- Dehydration, the most common cause of a mild rise.
- Reduced kidney function. See the kidney function test guide.
- A high-protein diet or protein supplements.
- Bleeding in the stomach or upper gut, since digested blood is protein.
- A blocked urinary tract, such as from an enlarged prostate.
- Heart failure, and medicines such as steroids.
The BUN to creatinine ratio helps: a ratio above about 20 suggests dehydration or another cause outside the kidneys, while a high BUN with a high creatinine and low eGFR points to the kidneys.
Call 911 or go to the ER if a high BUN comes with confusion or vomiting blood. Get care the same day for very little urine or black stools.
What causes low BUN?
Low BUN is usually not a concern. It's common with a low-protein or plant-based diet, drinking a lot of fluid, and pregnancy. Less often it reflects severe liver disease or malnutrition.
If your BUN is off at Passion Health
A Texas-licensed clinician reviews every result and calls you the same day about anything critical. One result outside the range is common and often harmless; we read it with the rest of your panel, your history and your medicines, and recheck when that's the sensible next step.
We read BUN with creatinine, eGFR and your hydration, and recheck after you've been drinking normally. If kidney function is the question, we add a urine albumin test; the Diabetes & Kidney Panel ($69) includes both.
BUN test cost in Texas
Self-pay. BUN comes with every comprehensive metabolic panel. In Essential Blood Work ($59) it's part of 33 results with the draw and a clinician's review included; on its own, the metabolic panel is $20 plus the $29 draw and review fee ($49).
With insurance. If we're in network with your plan, we bill it when the test is covered. You pay cash for a test only after we tell you the price in writing, and Medicare patients sign an Advance Beneficiary Notice first.
BUN blood test questions
What is BUN in a blood test?
BUN, blood urea nitrogen, measures urea, a waste product from protein that your kidneys clear. It's part of a comprehensive metabolic panel, and the typical range is about 6 to 20 mg/dL.
What does a high BUN mean?
Most often dehydration or a high-protein diet. It can also mean reduced kidney function, bleeding in the upper gut or heart failure. Your clinician reads it with creatinine and eGFR.
What does a low BUN mean?
Usually nothing serious: a low-protein diet, drinking a lot of fluid or pregnancy. Rarely it reflects severe liver disease or malnutrition.
What is a normal BUN to creatinine ratio?
Roughly 10 to 20. A higher ratio suggests dehydration or another cause outside the kidneys; when both BUN and creatinine are high with a ratio in that range, the kidneys are the more likely source.
Can drinking water lower BUN?
If BUN is high from dehydration, yes: drinking normally usually brings it back down. Water won't fix a BUN that's high because of kidney disease.