EmpeiriaUrea nitrogen
Also known as
BUN, blood urea nitrogen, urea
CH₄N₂O small molecule
What this substance is
- formula
- CH₄N₂O
- mass
- 60.056 g/mol
- monoisotopic
- 60.03236
- charge
- 0
- InChIKey
- XSQUKJJJFZCRTK-UHFFFAOYSA-N
- ChEBI
- CHEBI:16199
Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.
3D model · Urea nitrogen
Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.
Reference ranges
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This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.
How it is measured
In practice
A health worker takes a small blood sample from a vein in your arm with a needle. It usually takes less than five minutes. Usually you don't need to do anything to get ready. If other tests are done on the same blood, you may need to skip food and drink for several hours.
Serum, lithium heparin plasma or K2-EDTA plasma from venipuncture (urine is also acceptable for urea measurement); ammonium heparin must not be used. Separated serum or plasma should be removed from cells within one hour. No special preparation is usually needed unless other tests on the same sample require fasting. If kidney disease is suspected, creatinine and GFR may also be assessed.
Before the test
- Fast (no food or drink) for several hours only if your provider has ordered other tests that need it.
Where: laboratory
Sources: BUN (Blood Urea Nitrogen), MedlinePlus (U.S. National Library of Medicine); NHANES 2017-2018 Laboratory Procedure Manual, Blood Urea Nitrogen (BUN) (CDC National Center for Health Statistics) cited · not yet checked by a person
In the lab
Urease / glutamate dehydrogenase (kinetic UV)
Urea is a waste product your liver makes and your kidneys remove. The machine uses two helper proteins to break urea down, and that uses up a chemical that soaks up ultraviolet light. How much of it gets used up tells the machine how much urea there is.
A coupled enzyme reaction (urease, then glutamate dehydrogenase) converts urea while NADH is oxidised to NAD+; the change in NADH absorbance at 340 nm reflects the urea concentration.
- Read by: NADH absorbance decrease at 340 nm
Sources: Koerbin G et al. Bias Assessment of General Chemistry Analytes using Commutable Samples. Clin Biochem Rev 2014;35:203-211 (PMC4310060); NHANES 2017-2018 Laboratory Procedure Manual, Blood Urea Nitrogen (BUN), CDC/NCHS cited · not yet checked by a person
What it reports on
-
kidney
cleared by
The kidneys remove urea nitrogen from the blood, so high BUN can mean the kidneys are not working well.
-
liver
synthesized by
The liver turns ammonia into urea, so a failing liver can make BUN low.
Associated symptoms
Conditions this marker features in
-
high
High blood sodium
· supportive
Part of the standard work-up. A high urea nitrogen, especially with a high urea-to-creatinine ratio, points to dehydration as the cause.
-
high
Long-term reduced kidney function
· supportive
One of the tests used to check how well the kidneys are working.
-
high
Sudden loss of kidney function
· supportive
Urea (BUN) rises along with creatinine and has long been used to detect AKI. Trends in BUN and creatinine help decide when dialysis is needed.