Duhok Polytechnic University
Shekhan Technical College of Health
Estimation of Serum Urea
زانكـــويا بوليتــــةكنيكى يا دهـــؤك
جامعــــــــة دهــــــــــوك التقـــــنية
Duhok Polytechnic University 1
-Urea:
• Urea is the highest non-protein nitrogen compound in the blood.
• Urea is the major excretory product of protein metabolism.
• It is formed by urea cycle in the liver from free ammonia generated during protein
catabolism.
• Since historic assays for urea were based on measurement of nitrogen, the term blood
urea nitrogen (BUN) has been used to refer to urea determination.
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-Urea synthesis:
• Protein metabolism produces amino acids that can be oxidized.
• This results in the release of ammonia which is converted to urea (via urea cycle) and
excreted as a waste product.
• Following synthesis in the liver, urea is carried out in the blood to the kidney which is
readily filtered from the plasma by glomerulus.
• Most of the urea in the glomerular filtrate excreted in the urine, and some urea is
reabsorbed through the renal tubules.
• The amount reabsorbed depends on urine flow rate and extent of hydration (the
amount of urea reabsorbed increases with dehydration).
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-Urea synthesis:
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- Clinical Application:
• Measurement of urea used in :
• Evaluate renal function.
• To assess hydration status.
• To determine nitrogen balance.
• To aid in the diagnosis of renal diseases.
• Check a person's protein balance.
• verify adequacy of dialysis.
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1-Plasma urea Concentration:
• Measurement of Blood Urea Nitrogen (BUN) alone is less useful in diagnosing kidney
diseases because it’s blood level is influenced by dietary protein and hepatic function.
Type Cause Note
Pre-renal • Cognitive heart failure. Caused by reduced
High urea • Dehydration. renal blood flow, less
(High urea • High protein diet. blood is delivered to
concentration in plasma • Increased protein catabolism. kidney, then less urea is
is called azotemia) filtered.
Renal • Renal failure .
Post-renal • Urinary tract obstruction.
• Low protein intake.
Low urea • Liver disease.
• Pregnancy.
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Specimen collection
- Unhemolysed serum or heparinised plasma.
- Avoid flouride or ammonium as anticoagulant which interfere with the
assay.
urea is stable in serum or plasma for:
-24 hours at room temperature
-several day at 2-8 °C.
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-Objective:
• Estimation of Blood urea nitrogen (BUN).
-Principle (of the kit used):
- Enzymatic and colorimetric method is depends on the specific action of
urease which hydrolysis urea in ammonium ions and carbon dioxide.
Ammonium ions then form with chloride and salicylate a blue-green
complex. This coloration is proportional to urea concentration in the
specimen and measured at 600 nm.
• + H2O urease ------► NH4+ + CO2
• NH4+ + Cl- + Salicylate -------► green solution
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Urea test’s procedure:
Blank Standard Test
(Zeroing) (40 mg/dl) ( ? mg/dl)
WR (R1+R2) 1 ml 1 ml 1 ml
Standard (R4) - 10 µ -
Serum - - 10 µ
DW 10 µ - -
wait 5 minute at RT cº
R3 250 µ 250 µ 250 µ
wait 5 minute at 37 cº then read and calculate
Ab. (test)
Conc.(test) = X Conc.(standard) mg/dl
Ab.(standard)
-Reference Value:
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