A patient seated in the chair before a blood draw
In person

BUN (Urea Nitrogen)

A kidney and hydration marker, measured from one blood draw.

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  • 2,000+ lab locations. Find one near you
  • Nothing due at the lab. FSA / HSA accepted
  • Ordered by a licensed clinician

At a glance

Collection
Blood draw
A standard blood draw at the lab.
Preparation
None
Nothing to do ahead of time. Water is fine.
Results
1 to 2 days
Typical turnaround after your visit.
Where
2,000+ lab locations
Nationwide, with nothing due at the lab.

About this test

BUN, or blood urea nitrogen, measures urea, a waste product made when your body breaks down protein. Healthy kidneys clear it into urine, so BUN is read as a kidney marker, but hydration, diet, and illness can also move it. It is usually read with creatinine. No fasting is needed.

For adults 18 and older. Test availability varies by lab location.

Who should take this test?

This test is for adults who want to check a kidney marker, or whose healthcare provider follows BUN with creatinine during medication check-ins or after a past result.

Ask about this test

Not sure this is the right test?

AI-generated. For information only, not medical advice. Call 911 for an emergency.

What does this test measure?

Your result shows how much urea nitrogen is in your blood, which can help you and a healthcare provider read kidney function and hydration alongside creatinine.

Blood urea nitrogen (BUN)
Urea is a waste product your liver makes when it breaks down protein, and your kidneys clear it into urine. BUN measures the urea nitrogen in your blood. It can shift with hydration, the protein in your diet, and how well the kidneys are filtering, so it is read with creatinine.
Why it’s measured: To help gauge kidney filtering and hydration, read alongside creatinine.

How it works

  1. Step 1

    Order online

    Check out here. A licensed clinician in your state reviews your order and sends it to the lab.

  2. Step 2

    Visit a lab

    Bring a photo ID to any of 2,000+ lab locations. No fasting needed, and nothing is due at the lab.

  3. Step 3

    Get your results

    Results post to your account, usually in 1 to 2 days, each number next to the lab’s reference range.

Find a lab near you

Choose from 2,000+ lab locations nationwide. Your order works at any of them.

What your results tell you

BUN is reported in milligrams per deciliter (mg/dL) and compared with the lab’s reference range, which is shown on your report.

  • Your number next to the lab’s reference range
  • Explained in plain language
  • A licensed clinician reviews your order and, if appropriate, orders the test.
  • A lab report you can download and share

BUN can shift for reasons outside the kidneys, so talk with a healthcare provider about your result together with creatinine and eGFR.

Clinical-grade testing, from the comfort of home.

From the lab to your report, every step of our process meets the gold standard in medical testing.

  • CLIA-certified labs

    Every lab we partner with is certified under the Clinical Laboratory Improvement Amendments, meeting both state and federal standards with regular independent inspections.

  • We protect your health data

    We protect your health data with encryption and do not sell it. Some results must be reported to public health authorities by law. See our Privacy Notice.

  • Rigorous quality assurance

    All partner labs run regular internal quality checks, participate in proficiency testing, and comply with federal and state lab regulations.

  • Clinician-reviewed reports

    Results are reviewed by an independent, licensed clinician.

Questions

Common questions.

Anything else, our care team answers by phone, text, or email.

BUN can rise with a high-⁠protein diet, extra protein breakdown during a serious infection or fever, dehydration or reduced blood flow to the kidneys, kidney disease, or something blocking the flow of urine.

A low BUN is less common and can be seen with advanced liver disease or taking in a large amount of fluid.

Creatinine comes mostly from muscle and is a steadier kidney marker, while BUN also moves with diet, hydration, and illness. Looking at both, and at the ratio between them, can help a healthcare provider tell a hydration change from a kidney change.

Not on its own. BUN is one marker, and it can sit within the range even when other kidney measures are not. That is why it is usually read with creatinine, eGFR, and sometimes a urine albumin test. A healthcare provider can explain what your results mean together.

Lab tests are informational and don’t diagnose conditions on their own. Available to adults 18 and older; test availability varies by lab location. A licensed clinician reviews your order and, if appropriate, orders the test. All testing is performed at CLIA-certified laboratories. Not for emergencies: if you think you may be having a medical emergency, call 911.