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Removal of Blood Urea Nitrogen (BUN) from Critical Values List
In consultation with the Division of Nephrology, the Department of Pathology & Laboratory Medicine will remove blood urea nitrogen from the adult critical values list. Providers will no longer be required to accept verbal notification by the laboratory in cases of very elevated BUN values (>=80 mg/dL). This change is in harmonization with critical values reporting at all academic medical centers within the UC health system. There is no change to the pediatric critical values list. A complete list of critical values can be found here:

Effective date: September 4, 2019

Specimen requirement and testing information:

Specimen: Collect 4.0 mL whole blood in a light green (lithium heparin) tube. Red or gold top serum tube also acceptable. Invert tube 8 – 10 times to properly mix. Do not shake. Spin down and separate plasma from cells as soon as possible within 2 hours of sample collection.

Test methodology: Enzymatic

Test codes: BUN, BCRRT

Ambient: 2 hours
Refrigerated: 2 hours
Frozen: Unacceptable

After separation from cells:
Ambient: 8 hours
Refrigerated: 2 days
Frozen: 1 month

Turnaround time (TAT):
STAT: 60 minutes
Routine: 2 – 4 hours
Set Up Days: Daily

Specimen required: 1.0 mL plasma
Minimum volume: 0.5 mL plasma

Rejection criteria:
Specimens that exceed stated stability, unlabeled/mislabeled/mismatched specimens, specimens submitted in leaking containers and grossly hemolyzed specimens.

A summary of all tests offered by our laboratory services can be found here:


Bridgit O. Crews, PhD, DABCC
Clinical Chemistry & Toxicology

Edwin S. Monuki, MD, PhD
Department of Pathology & Laboratory Medicine
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