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BUN The protein waste your kidneys clear

Also called Blood urea nitrogen and Urea nitrogen Often on a standard checkup Fast for 12 hours

The short answer

BUN measures urea, the waste left when your body breaks down protein, which your kidneys clear. Labcorp’s range is 6 to 20 mg/dL for adults under 40, and its upper limit rises with age. On its own, BUN says less about your kidneys than creatinine and eGFR do.1,2,3,4

A good result
At Labcorp: 6 to 20 mg/dL under 40, 6 to 24 from 40 to 59 and 8 to 27 from 60.2,3,4
If yours is high
Dehydration, a high-protein meal, steroids and bleeding in the gut all raise it, as do kidneys that filter less. Your creatinine and eGFR help show whether your kidneys are the cause.1
Should you test?
You don’t need to order it on its own. It comes on the metabolic panel, next to creatinine and eGFR.3

Check your result

Type the number from your report. It stays on this page.

How old are you?

Labcorp’s range for BUN changes with age, so pick your age group. Your own report prints the range that applies to you.2,3,4

6 21
  • Low Under 6
  • In range 6 to 20
  • Above the range 21 or more

Enter your result to see what it means and what to do next.

Got a result from another lab? Ask Picardo about it. The app explains your results, and a physician can follow up.

Labcorp’s ranges are 6 to 20 mg/dL under 40, 6 to 24 from 40 to 59 and 8 to 27 from 60.2,3,4 The bar isn’t to scale.

What is a normal BUN level?

Labcorp’s range for adults under 40 is 6 to 20 mg/dL, and its upper limit rises with age.2,3,4 Read BUN alongside the creatinine and eGFR on the same report:1

Low Under 6 mg/dL; under 8 from age 60

Below the range

Low BUN is usually not a concern. It’s normal in pregnancy, and common with a low-protein diet or after IV fluids. Some liver diseases lower it, and so does holding on to too much water, which also lowers sodium.1

How worried to be

Not a worry on its own.

What to do next
  1. 1 Check the sodium on the same report. If it’s low too, or you have liver disease, show both results to a clinician.1
In range 6 to 20 mg/dL under 40; 6 to 24 at 40 to 59; 8 to 27 from 60

Within the range for your age

Your BUN is within the range Labcorp uses for your age.2,3,4

How worried to be

Nothing to worry about.

What to do next
  1. 1 Check the creatinine and eGFR on the same report. They’re better guides to how well your kidneys filter.1,5
Above the range 21 or more under 40; 25 or more at 40 to 59; 28 or more from 60

Above the range: find out why

Labcorp’s list of causes includes dehydration, even a moderate one, a high-protein meal, steroid medicines, bleeding in the stomach or gut, severe heart failure and kidneys that filter less.1

How worried to be

If it’s a little above the range, follow it up in the next week or two. If it’s far above, rose quickly or you feel unwell, get seen sooner, and the same day for black, tarry stools or vomiting blood.

What to do next
  1. 1 Look at your creatinine and eGFR. If they’re abnormal too, your kidneys may be filtering less.1,5
  2. 2 Check the BUN-to-creatinine ratio on your report. A high ratio fits dehydration or bleeding high in the gut, though it’s a rough guide.1,7
  3. 3 Before a retest, drink normally and skip a high-protein meal.1
Heart Health panel
$150.90 · BUN plus 16 more tests, one visit
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Or order just the comprehensive metabolic panel, $4.00

What is BUN?

Think of urea as the ash left after your body burns protein. Your kidneys sweep it out. Eat more protein or drink less water, and there’s more ash to clear.

When your body breaks down protein, from food or from its own tissues, it makes urea. Your kidneys filter urea into your urine, so it builds up when they filter less. BUN, short for blood urea nitrogen, measures how much is in your blood.1,5

Many things besides your kidneys move BUN, which is why labs report it next to creatinine.1

What raises BUN?

Labcorp lists these causes:1

  • Dehydration, even a moderate one
  • A high-protein meal, or a lot of protein in your diet
  • Bleeding in the stomach or gut
  • Steroid medicines, or tetracycline antibiotics taken with water pills
  • Severe heart failure
  • Kidney disease or a sudden kidney injury

Reading BUN next to creatinine helps tell these apart. The BUN-to-creatinine ratio on your report helps too, though it’s a rough guide.1,7

What does a low BUN mean?

Usually nothing worrying. BUN runs low in a normal pregnancy, on a low-protein diet and after IV fluids. Some liver diseases lower it too.1

How to lower BUN

BUN isn’t a target in itself. It comes down when you deal with what pushed it up:

  • Drinking enough

    Even moderate dehydration raises BUN, so getting enough fluid helps if you were running low.1

    How much it helps
    Some
    How sure we are
    Fairly sure
  • Treating the cause

    Bleeding, severe heart failure, steroid medicines and kidney disease each raise BUN, and each needs its own treatment.1

    How much it helps
    Some
    How sure we are
    Fairly sure
  • Less protein

    BUN rises with the protein you eat.1 If your eGFR is under 60, KDIGO suggests about 0.8 g of protein per kg of body weight a day, and no more than 1.3 g if your kidney disease is at risk of getting worse.5

    How much it helps
    A little
    How sure we are
    Fairly sure

Who should get a BUN test?

You don’t need to order it on its own. BUN comes on the comprehensive metabolic panel, so it’s part of most routine checkups.3 It’s most useful read with creatinine and eGFR, when checking for dehydration, kidney problems or bleeding in the gut.1,5

How to get a BUN test, and what it costs

It comes from the comprehensive metabolic panel, which costs $4.00 through Picardo. The Heart Health panel adds 16 more tests from the same visit for $150.90.

Recommended

Heart Health panel

$150.90
17 tests · fast for 12 hours first

BUN is most useful next to creatinine, eGFR and urine albumin. The panel has all of them, plus heart tests such as ApoB and Lp(a). See what’s in it

Order the Heart Health panel
Just this test

Comprehensive metabolic panel

$4.00
Labcorp 322000 · fast for 12 hours

The test this number comes from.

Order the comprehensive metabolic panel
  • Results in 2 to 3 days, in the app
  • Physician follow-up if you want one
  • Free Labcorp draw, or $75 at home
  • No other fees. HSA and FSA eligible.

It’s also part of the Base Core Annual – Men, Base Core Annual – Women, Brain Health Screening, Pregnancy, Postpartum, Fertility, Thyroid & Autoimmunity and Celiac / GI panels, if you want a wider checkup.

Already have a result? Ask Picardo about it

Questions people ask

What does a high BUN-to-creatinine ratio mean?

Labcorp’s range for the ratio is 9 to 20 for men and 9 to 23 for women aged 18 to 59. It’s higher from 60, such as 10 to 24 on a report for a 62-year-old man.2,3 A high ratio is traditionally read as dehydration or bleeding high in the gut.1 It’s a weak guide, though: in a study of over 3,600 hospital patients with sudden kidney injury, a high ratio didn’t behave like a sign of dehydration.7

Can a BUN test show bleeding in the stomach?

It can hint at it. In people known to be bleeding from the gut, a BUN-to-creatinine ratio over 30 raised the odds that it came from the stomach or upper gut about 7.5-fold.6 It can’t rule bleeding in or out on its own. Black, tarry stools need care the same day.

Why is my BUN high but my creatinine normal?

Dehydration, a high-protein meal, steroids and bleeding in the gut can all raise BUN while creatinine stays normal. Bleeding often raises the BUN-to-creatinine ratio too.1 If both numbers are high, your kidneys are more likely to be involved.1,5

Is BUN a good test of kidney function?

Not on its own. Diet, fluids, bleeding and medicines all move it. Clinicians judge kidney function from creatinine-based eGFR, adding cystatin C when needed, and read BUN alongside them.1,5

Often checked alongside

Creatinine
Muscle waste the kidneys filter out
eGFR
How well your kidneys filter
Urine albumin-to-creatinine ratio
Early kidney damage, from a urine sample
Cystatin C
Kidney filtration marker less affected by muscle mass than creatinine

Test details

Labcorp test
Metabolic Panel (14), Comprehensive, 322000
LOINC
3094-0
Sample
Blood
Fasting
12 hours for the metabolic panel
Typical lab range
6 to 20 mg/dL (ages 18 to 39); 6 to 24 mg/dL (40 to 59); 8 to 27 mg/dL (60 and older)2,3,4
Units
mg/dL of urea nitrogen in the US. For mmol/L of urea, multiply by 0.357.

Sources

  1. 1 Labcorp. Urea nitrogen (BUN), test 001040. Labcorp test menu. Accessed October 28, 2026. www.labcorp.com/tests/001040/urea-nitrogen
  2. 2 Labcorp. Pediatric testing reference ranges. Burlington, NC; 2022. Accessed October 28, 2026. www.labcorp.com/content/dam/labcorp/drupal/178250_DX_TL_PediatricTestRef_Final.pdf
  3. 3 Labcorp. Metabolic panel (14), comprehensive, test 322000. Sample report, collected October 28, 2022. Accessed October 28, 2026. files.labcorp.com/testmenu-d8/sample_reports/322000.pdf
  4. 4 Labcorp. Urea nitrogen clearance, test 002329. Sample report, collected December 19, 2019. Accessed October 28, 2026. files.labcorp.com/testmenu-d8/sample_reports/002329.pdf
  5. 5 Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117–S314. doi.org/10.1016/j.kint.2023.10.018
  6. 6 Srygley FD, Gerardo CJ, Tran T, Fisher DA. Does this patient have a severe upper gastrointestinal bleed? JAMA. 2012;307(10):1072–1079. doi.org/10.1001/jama.2012.253
  7. 7 Uchino S, Bellomo R, Goldsmith D. The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury. Clin Kidney J. 2012;5(2):187–191. doi.org/10.1093/ckj/sfs013

Updated 28 Oct 2026.

This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.