Urea Nitrogen, Urine

Urea Nitrogen, Urine

Synonym/acronym: N/A.

Common use

To assess renal function related to the progression of disorders such as diabetes, liver disease, and renal disease.


Urine (5 mL) from an unpreserved random or timed specimen collected in a clean plastic collection container.

Normal findings

(Method: Spectrophotometry)
Conventional UnitsSI Units (Conventional Units × 35.7)
12–20 g/24 hr428–714 mmol/24 hr


Urea is a nonprotein nitrogen compound formed in the liver from ammonia as an end product of protein metabolism. Urea diffuses freely into extracellular and intracellular fluid and is ultimately excreted by the kidneys. Urine urea nitrogen levels reflect the balance between the production and excretion of urea.

This procedure is contraindicated for



  • Evaluate renal disease
  • Predict the impact that other conditions, such as diabetes and liver disease, will have on the kidneys

Potential diagnosis

Increased in

  • Diabetes (related to increased protein metabolism)
  • Hyperthyroidism
  • Increased dietary protein (related to increased protein metabolism)
  • Postoperative period

Decreased in

    Liver disease (BUN is synthesized in the liver, so liver damage results in decreased levels) Low-protein/high-carbohydrate diet (urea nitrogen is a by-product of protein metabolism; less available protein is reflected in decreased BUN levels) Normal-growing pediatric patients (increased demand for protein; less available protein is reflected in decreased BUN levels) Pregnancy (increased demand for protein; less available protein is reflected in decreased BUN levels) Renal disease (related to decreased renal excretion) Toxemia (related to hypertension and decreased renal excretion)

Critical findings


Interfering factors

  • Drugs that may increase urine urea nitrogen levels include alanine and glycine.
  • Drugs that may decrease urine urea nitrogen levels include furosemide, growth hormone, insulin, and testosterone.
  • All urine voided for the timed collection period must be included in the collection or else falsely decreased values may be obtained. Compare output records with volume collected to verify that all voids were included in the collection.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:   Inform the patient this test can assist in assessing kidney function.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s genitourinary and hepatobiliary systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Provide a nonmetallic urinal, bedpan, or toilet-mounted collection device. Address concerns about pain and explain that there should be no discomfort during the procedure.
  • Usually a 24-hr time frame for urine collection is ordered. Inform the patient that all urine must be saved during that 24-hr period. Instruct the patient not to void directly into the laboratory collection container. Instruct the patient to avoid defecating in the collection device and to keep toilet tissue out of the collection device to prevent contamination of the specimen. Place a sign in the bathroom to remind the patient to save all urine.
  • Instruct the patient to void all urine into the collection device and then to pour the urine into the laboratory collection container. Alternatively, the specimen can be left in the collection device for a health-care staff member to add to the laboratory collection container.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection.
  • Random Specimen (Collect in Early Morning)

  • Clean-Catch Specimen
  • Instruct the male patient to (1) thoroughly wash his hands, (2) cleanse the meatus, (3) void a small amount into the toilet, and (4) void directly into the specimen container.
  • Instruct the female patient to (1) thoroughly wash her hands; (2) cleanse the labia from front to back; (3) while keeping the labia separated, void a small amount into the toilet; and (4) without interrupting the urine stream, void directly into the specimen container.
  • Indwelling Catheter

  • Put on gloves. Empty drainage tube of urine. It may be necessary to clamp off the catheter for 15 to 30 min before specimen collection. Cleanse specimen port with antiseptic swab, and then aspirate 5 mL of urine with a 21- to 25-gauge needle and syringe. Transfer urine to a sterile container.
  • Timed Specimen

  • Obtain a clean 3-L urine specimen container, toilet-mounted collection device, and plastic bag (for transport of the specimen container). The specimen must be refrigerated or kept on ice throughout the entire collection period. If an indwelling urinary catheter is in place, the drainage bag must be kept on ice.
  • Begin the test between 6 and 8 a.m. if possible. Collect first voiding and discard. Record the time the specimen was discarded as the beginning of the timed collection period. The next morning, ask the patient to void at the same time the collection was started and add this last voiding to the container. Urinary output should be recorded throughout the collection time.
  • If an indwelling catheter is in place, replace the tubing and container system at the start of the collection time. Keep the container system on ice during the collection period, or empty the urine into a larger container periodically during the collection period; monitor to ensure continued drainage, and conclude the test the next morning at the same hour the collection was begun.
  • At the conclusion of the test, comparethe quantity of urine with the urinary output record for the collection; if the specimen contains less than what was recorded as output, some urine may have been discarded, invalidating the test.
  • Include on the collection container’s label the amount of urine, test start and stop times, and ingestion of any medications that can affect test results.
  • General

  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Nutritional Considerations: An elevated BUN can be caused by a high-protein diet or dehydration. Unless medically restricted, a healthy diet consisting of the five food groups of the USDA's MyPlate dietary guide should be consumed daily. Water consumption should include six to eight 8-oz glasses of water per day, or water consumption equivalent to half of the body’s weight in fluid ounces (32 fl oz = 1 qt; 34 fl oz = 1 L).
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include anion gap, antibiotic drugs, biopsy kidney, BUN, calcium, calculus kidney stone panel, CT spleen, creatinine, creatinine clearance, cytology urine, cystoscopy, electrolytes, gallium scan, glucose, glycated hemoglobin, 5–HIAA, IVP, ketones, magnesium, microalbumin, osmolality, oxalate, phosphorus, protein total and fractions, renogram, US kidney, UA, and uric acid.
  • Refer to the Genitourinary and Hepatobiliary systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners