Urea Nitrogen, Blood

Urea Nitrogen, Blood is a topic covered in the Davis's Lab & Diagnostic Tests.

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To assist in assessing for kidney function toward diagnosing disorders such as kidney disease and dehydration. Also used in monitoring the effectiveness of therapeutic interventions such as hemodialysis.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Spectrophotometry.

AgeConventional UnitsSI Units (Conventional Units × 0.357)
Newborn–3 yr5–17 mg/dL1.8–6.1 mmol/L
4–13 yr7–17 mg/dL2.5–6.1 mmol/L
14 yr–adult8–21 mg/dL2.9–7.5 mmol/L
Adult older than 90 yr10–31 mg/dL3.6–11.1 mmol/L

Critical Findings and Potential Interventions


  • Greater than 100 mg/dL (SI: Greater than 35.7 mmol/L) (nondialysis patients)


  • Greater than 55 mg/dL (SI: Greater than 19.6 mmol/L) (nondialysis patients)

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

A patient with a grossly elevated BUN may have signs and symptoms including acidemia, agitation, confusion, fatigue, nausea, vomiting, and coma. Possible interventions include treatment of the cause, administration of IV bicarbonate, a low-protein diet, hemodialysis, and caution with respect to prescribing and continuing nephrotoxic medications.

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