Serum Urea By 54 Fifth Stage Student Dr. Sakar Karem Abdulla M.Sc. Clinical Biochemistry

Urea Urea is the end product of protein metabolism produced mainly in the liver by urea cycle. Urea is the major nitrogenous excretory product and harmless compound serves as the disposal form of ammonia which is toxic.

Structure of urea Urea composed of two amino (NH2) groups and a linked carbamyl (C-O) group.

Steps of urea cycle Formation of carbamoyl phosphate Formation of citrulline Formation argininosuccinate Cleavage of argininosuccinate Cleavage of arginine

Steps of urea cycle

Fate of urea Urea formed in the liver is transported through circulation to kidneys for excretion through urine It is also transported to intestine where it is decomposed by urease, ammonia liberated by this activity is transported to liver where detoxified back to urea also a fraction of ammonia goes to systemic circulation.

Fate of urea

Role of alanine in transporting amino acid nitrogen to the liver In muscle glucose metabolise by glycolysis to produce pyruvate Pyruvate is transaminated by glutamate to form alanine which travel to liver In the liver alanine converted back to pyruvate and nitrogen

Role of alanine in transporting amino acid nitrogen to the liver

Role of glutamine in transporting amino acid nitrogen to the liver Glutamine is synthesized from glutamate by glutamin synthetase which found in all cells. The glutamine travels to the liver where by glutaminase convert to glutamate plus ammonia. The ammonia is used for urea biosynthesis

Role of glutamine in transporting amino acid nitrogen to the liver

Causes for elevated plasma urea Prerenal can be caused by: decreased blood flow through the kidneys (e.g. low blood pressure, congestive heart failure, shock, bleeding, dehydration). increased production of urea in the liver via a high protein diet or increased protein catabolism (e.g. starvation, tissue damage, sepsis, steroid treatment).

Causes for elevated plasma urea 2) Renal causes can be attributed to decreased kidney function which include: acute and chronic kidney failure acute and chronic glomerular nephritis tubular necrosis

Causes for elevated plasma urea 3) Post renal causes can be due to urinary outflow obstruction such as by: calculi or tumours of the bladder Prostate severe infection

Causes for reduced plasma urea low-protein diet pregnancy due to the combined effect of reduced urea production and increased urea excretion Overhydration induces increased GFR and consequent increased excretion of urea. Inherited deficiency of urea cycle enzyme liver disease Reduced plasma urea is less common and usually of less clinical significance than increased plasma urea.

S.Urea test S.Urea one of the renal function test which indicated the level of urea in circulation. Also can be expressed as blood urea nitrogen(BUN). Normal range Serum urea 15-40 mg/dL Serum BUN 7-20 mg/dL

Principle of the test urea + H2O urease -------> 2 NH4+ + CO2 ( by urease) NH4 + + salicylate+ NaCIO----->indophenol ( by nitroprusside)

procedure Reagents Standard Assay Reagent (A) 1000 µl standard 10µl serum 10 µl Mix and incubate for 10 minutes at room temperature Reagent (B) Read the absorbance at 600 nm, the colour is stable for 2 hours.

Calculation S.Urea=Abs.Assay/Abs.standard x conc.standard (50 mg/dl) BUN= S.Urea/2