Renal
Urea
Urea is the main nitrogen-containing waste product of protein metabolism, formed in the liver and cleared from the blood by the kidneys. It is a core renal marker, usually reported alongside creatinine and electrolytes to give a quick picture of kidney function, hydration and protein balance.
Why it is measured
Urea is measured to support assessment of kidney function, hydration status and protein turnover, with a raised urea relative to creatinine often prompting consideration of dehydration or an upper gastrointestinal bleed. Near-patient testing allows rapid renal assessment in acute, critical care, dialysis and community settings.
| Typical range | Indicative adult serum or plasma urea: approximately 2.5 to 7.8 mmol/L. Many US point-of-care devices report blood urea nitrogen (BUN) instead: approximately 7 to 22 mg/dL, equivalent to roughly 2.5 to 7.8 mmol/L of urea, since urea in mmol/L is about BUN in mg/dL divided by 2.8. Ranges vary by method, population, age and individual laboratory, so always read against the issuing service's quoted interval. |
|---|---|
| Sample | Whole blood (arterial, venous or capillary), plasma or serum, depending on the platform. Lithium heparin is the usual anticoagulant for whole-blood cartridge and sensor-card systems. |
| Turnaround | Around 2 to 3 minutes on handheld cartridge analysers such as the i-STAT, roughly 1 to 2 minutes on whole-blood critical care analysers, and around 12 minutes on disc-based benchtop chemistry systems such as the Piccolo Xpress. Exact times vary by platform and the panel selected. |
Point of care devices that report it
- Abbott i-STAT 1 and i-STAT Alinity (BUN/urea cartridges)
- Abaxis Piccolo Xpress (Renal Function, Kidney Check, Basic and Comprehensive Metabolic panels)
- Nova Biomedical Stat Profile Prime Plus (whole-blood critical care analyser, BUN/urea)
- Siemens Healthineers epoc Blood Analysis System (BUN/urea)
Questions, answered
Is urea the same as BUN?
They measure the same molecule but report it differently. Blood urea nitrogen (BUN), common on US point-of-care devices, quantifies only the nitrogen portion, whereas urea, common in UK and European reporting, reflects the whole molecule. To convert, multiply BUN in mg/dL by about 0.357 to get urea in mmol/L, or multiply urea in mmol/L by about 2.8 to get BUN in mg/dL.
Why is urea reported together with creatinine?
Both are nitrogenous wastes cleared by the kidneys, but they behave differently. Urea is strongly influenced by hydration, protein intake and gastrointestinal bleeding, while creatinine tracks more closely with filtration. Reviewing them together, including the urea-to-creatinine ratio, can help distinguish patterns such as dehydration from intrinsic kidney problems, though clinical interpretation rests with the treating clinician.
Can a point-of-care urea result replace a laboratory result?
Near-patient urea is designed for rapid assessment and triage, and well-maintained devices generally correlate closely with laboratory analysers. Local policy usually defines when a point-of-care result needs laboratory confirmation, particularly near clinical decision limits or when quality control is out of range. Method and calibration differences mean results should not be interchanged across platforms without local validation.