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Test ID: Urea
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Urea
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Useful For
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Assessment of renal function and diagnosis of renal disorders.
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Method name and description
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Kinetic test with urease and glutamate dehydrogenase.2,3,4,5
Urea is hydrolyzed by urease to form ammonium and carbonate.
Urease
Urea + 2 H2O  2 NH4+ + CO3 2-
In the second reaction 2‑oxoglutarate reacts with ammonium in the
presence of glutamate dehydrogenase (GLDH) and the coenzyme NADH to
produce L‑glutamate. In this reaction two moles of NADH are oxidized to
NAD+ for each mole of urea hydrolyzed.
GLDH NH4+ + 2‑oxoglutarate + NADH L‑glutamate + NAD+ + H2O
The rate of decrease in the NADH concentration is directly proportional to
the urea concentration in the specimen and is measured photometrically.
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Clinical information
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Urea is the major end product of protein nitrogen metabolism. It is synthesized by the urea cycle in the liver from ammonia which is produced by amino acid deamination. Urea is excreted mostly by the kidneys but minimal amounts are also excreted in sweat and degraded in the intestines by bacterial action.
Determination of blood urea nitrogen is the most widely used screening test for renal function. When used in conjunction with serum creatinine determinations it can aid in the differential diagnosis of the three types of azotemia: prerenal, renal and postrenal.
Elevations in blood urea nitrogen concentration are seen in inadequate renal perfusion, shock, diminished blood volume (prerenal causes), chronic nephritis, nephrosclerosis, tubular necrosis, glomerular nephritis (renal causes) and urinary tract obstruction (postrenal causes). Transient elevations may also be seen during periods of high protein intake. Unpredictable levels occur with liver diseases.
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Specimen type / Specimen volume / Specimen container
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Specimen type: Serum, Plasma
Minimum volume of sample: 1 mL
Serum: Plain tube (red or yellow top)
Plasma: Li‑heparin tube
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Collection instructions / Special Precautions / Timing of collection
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Collect blood by standard venipuncture techniques as per specimen requirements. When processing samples in primary tubes (sample collection systems), follow the instructions of the tube manufacturer.
DO NOT use ammonium heparin.
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Storage and transport instructions
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Storage: 7 days at 15 – 25°C
7 days at 2 – 8°C
1 year at ‑15 to -25°C
Transport: 2-25°C
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Specimen Rejection Criteria
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- Grossly hemolyzed specimen.
- Icteric specimen
- Lipemic specimen.
- Wrong collection container.
- Specimen with insufficient quanitity .
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Biological reference intervals and clinical decision values
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| Gender |
Age |
Reference Interval (mmol/L) |
| Female / Male |
0 Minutes - 28 Days |
0.8 - 5.5 |
| Female / Male |
28 Days - 1 Year |
1.0 - 5.5 |
| Female / Male |
1 Year - 16 Years |
2.5 - 6.5 |
| Female / Male |
16 Years - 150 Years |
2.5 - 7.8 |
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Factors affecting test performance and result interpretation
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Ammonium ions may cause erroneously elevated results.
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Turnaround time / Days and times test performed / Specimen retention time
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Daily (24/7)
Turn-around time:
STAT: 1 hour
Routine: One working day
Specimen Retention: 4 days
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