Urea Nitrogen

Additional Information:

Serum free from hemolysis is the recommended specimen.

UFHPL Epic order code: LAB140

CPT Code(s):


Specimen Requirements:

Type: Serum or plasma

Container/Tube: Serum gel or heparinized plasma

Sample Volume: Submit the full tube.

Minimum Volume: 0.5 mL serum or plasma


  1. Send specimens in their original tubes.
  2. Centrifuge the tube if there is a delay in transport of more than 1 hour.

  • Samples are stable for up to 1 day at 15 – 25°C.
  • Samples are stable for up to 3 days at 2 – 8ºC.

Unacceptable Conditions: Samples with moderate or marked hemolysis will be rejected.

Specimen Retention Time: 5 days


Measurements of urea nitrogen are used in the diagnosis and treatment of certain renal and metabolic disorders. Blood urea nitrogen (BUN) levels are a measure of kidney function and also of pre- and post-renal conditions.


Urea is hydrolyzed enzymatically by urease to yield ammonia and carbon dioxide. The ammonia and a–oxoglutarate are converted to glutamate in a reaction catalyzed by L-glutamate dehydrogenase (GLDH). Simultaneously, a molar equivalent of reduced NADH is oxidized. The rate of change in absorbance at 340 nm, due to the disappearance of NADH, is directly proportional to the BUN concentration in the sample.


Within 24 hours

Reference Values:

6-21 mg/dL