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Test Name:
Urea Clearance
- SBMF No:
23224 - Performance Lab Name:
Automated Lab - Test Mnemonic:
U UR CLEAR - CPT Code:
84545 - LOINC Code:
11064-3; 11065-0; 30211-7; 3167-4; 12967-6; 51735-9 - Also Known As:
Residual Clearance - Spec Type:
Serum + Urine, 44-hour collection - Spec Container:
Gold top (SST) or red top (serum) tube –plus– plastic container with tightly fitting lid - Alt Spec Type:
Plasma + Urine, 44-hour collection - Alt Spec Container:
Lavender top (EDTA) or green top (lithium heparin) tubes + plastic container with tightly fitting lid (no preservative) - Pref Vol:
1.0 mL serum or plasma (each of 2 specimens) + 10.0 mL aliquot of well-mixed 44-hour urine collection - Min Vol:
0.3 mL serum or plasma (each of 2 specimens) + 1.0 mL aliquot of well-mixed 44-hour urine collection - Spec Collect:
Serum or plasma:
– Routine venipuncture
– Collect first , "0-hour", specimen following a dialysis
– Collect second, "44-hour", specimen prior to next dialysis, two days later
– Label specimens appropriately: "0-hour" and 44-hour"
Urine, 44-Hour Collection:
– To begin collection of timed specimen, have patient urinate, noting date and exact time
– Discard this first portion of urine, but document date and time of voiding on container label and test requisition as "start" of timed specimen
– Save all urine voided during designated time period, including portion voided at exact end of time period (44 hours)
– IMPORTANT: Refrigerate entire specimen (2-8°C) during and after collection to prevent bacterial growth
– Document date and time of final voiding on label and requisition as "end" of timed specimen - Spec Process:
Serum or plasma:
– Serum sample tubes, clot 30 minutes
– All tubes, centrifuge 15 min
– Immediately transfer serum from red top tube or plasma from lavender top or green top tube to separate plastic tube
– Properly centrifuged gel barrier tube sample does not require transfer of serum to separate tube
Urine, 44-Hour Collection:
– Upon completion of collection, mix entire specimen very well, and measure 44-hour volume
– Pour off 10.0 mL of urine into separate plastic tube(s)
– Refrigerate urine aliquot and transport refrigerated
– Send urine aliquot with notation of entire 44-hour urine volume on aliquot label and on requisition - Spec Store Transport:
Refrigerated - Spec Stability:
Serum or plasma:
– 1 week room temperature (20-30°C)
– 1 week refrigerated (2-8°C)
– 1 year frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles
Urine, 44-Hour Collection aliquot:
– 48 hours room temperature (20-30°C)
– 1 week refrigerated (2-8°C)
– 1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Methodology:
Enzymatic - Use:
Renal function test - Clinical Significance:
Urea is synthesized in the liver from ammonia produced as a result of deamination of amino acids. This biosynthetic pathway is the chief means of excretion of surplus nitrogen by the body.
The determination of serum urea nitrogen is presently the most widely used screening test for the evaluation of kidney function. Increased levels of serum urea nitrogen may be due to pre-renal causes (cardiac decompensation, water depletion due to decreased intake or excessive loss, increased protein catabolism). Among the renal causes are acute glomerulonephritis, chronic nephritis, polycystic kidney, nephrosclerosis, and tubular necrosis. Post-renal causes include all types of obstruction of the urinary tract (stone, enlarged prostate gland, tumors. - Reference Range:
Serum or plasma urea nitrogen (non-renal patient): 8–23 mg/dL
Non-renal patient residual clearance: 7–13 mL/min - Day Run:
Sun-Sat (daily) - Time Run:
As received - Time Reported:
4 hours - Test Type:
CHEMISTRY
