Urea PDF

: also known as carbamide ( is the major nitrogenous end product of protein and amino acid catabolism ,Urea is a white crystalline substance containing two amino (NH2) groups and a linked carbamyl (C-O) group: the chemical formula NH2-CO-NH2; it is highly water soluble and contains 46% n...

: also known as carbamide ( is the major nitrogenous end product of protein and amino acid catabolism ,Urea is a white crystalline substance containing two amino (NH2) groups and a linked carbamyl (C-O) group: the chemical formula NH2-CO-NH2; it is highly water soluble and contains 46% nitrogen Urea synthesis : Protein metabolism produces amino acids in the liver which are in turn degraded (deaminated), to produce ammonia (NH3), which is toxic , Ammonia is then converted to urea via (urea cycle) urea is carried out in the blood which is readily filtered from the plasma by the kidney ,most of the urea produced in the liver is transported in blood to the kidneys where it is eliminated from the body in urine. The urea cycle is a series of biochemical reactions that results in toxic ammonia resulting from protein breakdown is converted to non-toxic urea. which is excreted as a waste product ,This is the most important catabolic pathway for eliminating excess nitrogen in the human body Urea levels tend to be slightly higher in males than in females Clinical Significance :Measurement of urea used in : -Evaluation renal function (as an index of renal function) -To assess hydration status -To aid in the diagnosis of renal diseases the high level of urea occur due to reduced urinary elimination and associated marked reduction in glomerular filtration rate (GFR). Normal range of serum urea: 20-40 mg/dL 3.3- 6.6 mmol/L States associated with elevated levels of urea in blood are referred to as Uremia is a disorder of kidney function associated with accumulation of toxic substances where urea accumulates in the blood due to the inability of the kidneys to remove it from the blood , It is characterized by fluid, electrolyte, hormonal, and metabolic abnormalities. the main cause of uremia is chronic and acute renal disease Causes of urea plasma elevations: 1- high-protein diet 2- excessive protein catabolism 3- renal failure 4- Urinary tract obstruction 5- Hemorrhage ,severe burns, severe infections, tissue damage 6- dehydration, heart failure 7- treatment with medicines like cortisol, 8- ageing Decreased BUN levels are associated with the following conditions : 1. Liver failure ,advanced liver disease The liver plays a vital role in urea production via the urea cycle so any genetic defects of any urea cycle enzymes can lead to reduced urea synthesis. and consequent reduced serum urea concentration. 2. Impaired absorption 3. Malnutrition , low-protein diets 4-pregnancy:the reduced serum urea that commonly occurs during pregnancy is due to the combined effect of reduced urea production and increased urea excretion Measurement of Blood urea alone is less useful in diagnosing kidney diseases 1-because it is influenced by factors such as High protein diet , variables in protein synthesis , patient hydration status. 2- Any condition of increased proteins catabolism will increase urea formation : (Cushing syndrome, diabetes mellitus, starvation) 2- urea is partially reabsorbed by the renal tubules Urea is expressed as the whole molecule (not just the nitrogen part of the molecule) Since BUN reflects only the nitrogen content of urea (MW 28) and urea measurement reflects the whole of the molecule (MW 60), urea is approximately twice (60/28 = 2.14) that of BUN. Thus BUN mg/dL is equivalent to urea 2.14 mg/dL. Determination of urea in the blood using Urease/Salycilate Enzymatic colorimetric method is hydrolyzed by urease into ammonia and carbon dioxide The ammonia generated reacts with alkaline hypochlorite and sodium salicylate in presence of sodium nitroprusside as coupling agent to yield a green cromophore. The intensity of the color formed is proportional to the concentration of urea in the sample  Nitroprusside NH4+ Sakicylate + NaClO +OHˉ ---------------- Indophenol + NaCl : Reagent A= (R1:Urease + R2: Sodium Salicylate and Sodium Nitroprusside) Reagent B = (R3: Sodium hypochlorite) blank Standard Test Distilled water 10 µL ------- Reagent A 1 mL 1 mL 1 mL Standard solution --------- 10 µL -------- Serum --------- 10 µL Mix well and incubate for 5 minutes at 37°C 1 mL 1 mL 1 mL Mix well and incubate for 5 minutes at 37°C Read the absorbance (A) of the samples and the standard at 600 nm against the reagent blank. Calculation: A Sample/ A Standard (Standard Concentration of Urea) 1- A Sample/ A Standard X 50 mg/dL 2- A Sample/ A Standard X 8.3 mmol\L 3- A Sample/ A Standard X 23.3 mg/dl