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Test Code BUN Urea Nitrogen, Plasma

Specimen Type

Preferred: Plasma

Acceptable: Serum


Preferred: Lithium Heparin (Mint Green or Dark Green)

Acceptable: Serum (Red Top tube or Gold SST)

Preferred Volume

5 mL

Offsite Collection Instructions

1. Serum and plasma tubes should be centrifuged and aliquoted within 2 hours of collection.

2. Aliquoted samples could either be room temperature at 15-25°C or refrigerated at 2-8°C prior and during transportation.

3. If above criteria are not met, specimen will be rejected.

UCMC Collection Instructions

1. Samples need to be received in the lab within 2 hours of collection at room temperature.

2. Greater than 2 hours must be refrigerated at 2-8°C.

3. If the specimen cannot be sent to the lab within 6 hours of collection, it must be spun, aliquoted and refrigerated at 2-8°C.

4. All unspun specimens greater that 6 hours will be rejected.  

5. If above criteria are not met, specimen will be rejected.



Turnaround Time

4 hours

STAT Availability


Test Usage

The determination of urea is the most widely used test for the evaluation of kidney function. The test is frequently used in conjunction with the determination of creatinine for the differential diagnosis of prerenal hyperuremia (cardiac decompensation, water depletion, increased protein catabolism), renal hyperuremia (glomerulonephritis, chronic nephritis, polycystic kidney, nephrosclerosis, tubular necrosis) and postrenal hyperuremia (obstructions of the urinary tract).

Test Methodology

Spectrophotometric, kinetic

CPT Code


STAT Turnaround Time

1 hour

Reference Range

7 – 20 mg/dL

Critical Results


Minimum Volume

2 mL

Fee Code




Test Includes

Quantitative determination of urea/urea nitrogen in plasma