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Lab Manual for Moffitt-Long and Mount Zion

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Urea Clearance

Item Value
Approval req'd? Yes, if testing is requested between midnight and 8:00 AM.
Available Stat? No
Test code URCL
Test group Urea
Performed by Parnassus Chemistry
In House Availability Test available 7 days per week from 8:00 AM to midnight only.
Method Enzymatic conductivity, kinetic (urease)
Collection Instructions Refrigerate the collection container during the collection period.

Submit serum (Gold top) drawn within 24 hours of urine collection-preferably within the interval of collection.

Include the patient's weight in kg and height in cm on the requisition if a corrected clearance is needed.
Container type 24 hour urine container AND Gold top vacutainer

Click here for Urine Preservative Requirements
Amount to Collect Entire 24 hour urine output
2 ml blood
Sample type 24 hour urine AND serum
Preferred volume
Urine Complete collection
Serum 1 mL
Min. Volume
Urine Complete collection
Serum 0.2 mL
UCSF Rejection Criteria Container not refrigerated during collection.
Units mL/min/1.73 m2
Normal range See additional information
Stability Refrigerated 2 days.
Turn around times 4 hours
Additional information In normal individuals, urea clearance ranges between 35% - 65% of the GFR depending on hydration status (Diseases of the Kidney and Urinary Tract, R.W Schrier, 8th edition, 2007).

Note: Clearances are often inaccurate because of incomplete urine collection. A 4- or 6-hour collection is likely to be more complete than the classic 24 hour test, but extrapolation of results from shortened collections may not be accurate.

An order for Urea Clearance includes the following parameters:

a. Urine Urea Nitrogen: (Urine urea nitrogen mg/dL x Total Vol in mL x 24) / (100,000 x hours of collection) = g/d

Note: Only Urine Urea Nitrogen will be reported if no serum sample is received.

b. Urea Clearance Uncorrected: (Urine urea nitrogen mg/dL x Total Volume mL) / (60 x hours of collection x serum urea nitrogen) = mL/min

c. Corrected Urea Clearance: (Total Vol. in mL x urine urea nitrogen mg/dL x 1.73) / (60 x hours of collection x serum urea nitrogen x surface area) = mL/min/1.73 m2
Last Updated 1/30/2013 12:22:44 PM
Entry Number 1169
Lab Procedure Link Click here for Procedure
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