Page 93 - Clinical Biochemistry

Measurement of non-protein nitrogen containing compounds

Catabolism of proteins and nucleic acids results in formation of non-protein nitrogenous
compounds. Protein, Amino acids, Ammonia, Urea.

1- Urea

Serum Urea: 8-20 mg/dl

Urea is formed in the liver from ammonia.

Over 75% of non-protein nitrogen is excreted as urea mainly by the kidneys.

Blood urea level is sensitive but not specific indicator for renal dysfunction, because:

• Its level is affected by dietary protein
• Other non-renal causes such as heart failure and blood pressure may affect its level.
• Its level is elevated in last stages of renal failure after 50% of renal function is lost.

High serum urea can indicates:

• Renal insufficiency. (due to obstruction or cancer)
• Urinary tract blockage (by a kidney stone or tumor)
• Heart failure (poor renal perfusion: low blood flow to kidney).
• Dehydration (lack of fluid volume to excrete waste products).
• High-protein diet
• Some medicines.

Low serum urea may be due to:

• Very low protein diet as in malnutrition
• Severe liver damage inhibits urea cycle, decrease urea formation and increase free ammonia

leads to hepatic comma.
• Overhydration.

2- Uric acid:

• Is the end product of purine metabolism and excreted in urine.
• Purine in body comes from food and break down of body cells.
• Elevated level of uric acid in blood is one of the markers of kidney dysfunction.