Davis's Lab & Diagnostic Tests
Urea Nitrogen, Blood and Urea Nitrogen, Urine
General
Core Lab Study
Synonym/Acronym:
BUN.
A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.
Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.
BUN, often collected with and compared to creatinine levels, is included in the Basic Metabolic panel, Comprehensive Metabolic panel (CMP), General Health panel, Hypertension panel, and Renal panel. Panels are used as general health and targeted screens to identify or monitor conditions such as bone disease, diabetes, hypertension, kidney disease, liver disease,or malnutrition.
Rationale
Blood and Urine: To assist in screening for kidney function toward diagnosing disorders such as kidney disease and dehydration. Also used in monitoring the effectiveness of therapeutic interventions such as dialysis. Urine: Used as an indicator of nitrogen balance for assessing malnutrition and optimizing hyperalimentation treatment.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction. For urine studies, usually a 24-hr urine collection is ordered. As appropriate, provide the required urine collection container and specimen collection instructions.
Normal Findings
Method: Spectrophotometry.
| Blood | ||
|---|---|---|
| Age | Conventional Units | SI Units (Conventional Units × 0.357) |
| Blood Urea Nitrogen (BUN) | ||
| Newborn–3 yr | 5–17 mg/dL | 1.8–6.1 mmol/L |
| 4–13 yr | 7–17 mg/dL | 2.5–6.1 mmol/L |
| 14 yr–adult | 8–21 mg/dL | 2.9–7.5 mmol/L |
| Pregnancy (second to third trimester) | 5–12 mg/dL | 1.5–4.5 mmol/L |
| Adult older than 90 yr | 10–31 mg/dL | 3.6–11.1 mmol/L |
| BUN/Cr Ratio | ||
| 10:1 to 20:1 | ||
| Urine | |
|---|---|
| Conventional Units | SI Units (Conventional Units × 35.7) |
| 12–20 g/24 hr | 428–714 mmol/24 hr |
Critical Findings and Potential Interventions
Blood: Adults
- Greater than 100 mg/dL (SI: Greater than 35.7 mmol/L) (nondialysis patients)
Blood: Children
- 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, dialysis, and caution with respect to prescribing and continuing nephrotoxic medications.
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