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

2. 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.

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

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

5. Steps of urea cycle

6. 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.

7. Fate of urea

8. 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

9. Role of alanine in transporting amino acid nitrogen to the liver

10. 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

11. Role of glutamine in transporting amino acid nitrogen to the liver

12. 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).

13. 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

14. 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

15. 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.

16. 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 mg/dL Serum BUN 7-20 mg/dL

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

18. 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.

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