Blood Urea Nitrogen (BUN | F)
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What are the functions of kidney (including its corresponding mechanisms)?
1) Blood, waste, and H2O enter through the renal artery 2) Filtered blood or excess H2O leave through the renal vein 3) Excess H2O and toxic waste in the form of urine leave via the ureter
Excess H2O and toxic waste are excreted in the form of what?
Urine
What are the roles of the kidney?
1) Excretion 2) Homeostasis 3) Osmoregulation 4) Regulation of salts in the body 5) Regulation of pH 6) Production of a hormone (EPO)
What is the meaning of NPN?
Non-protein nitrogen
What is an NPN?
It is the major substance excreted by the kidneys
What is azotemia?
Elevated NPNs in the blood
What is elevated if the pt has azotemia?
Urea
What is uremia?
Azotemia + acidosis + electrolyte imbalance (hyperkalemia)
What are the clinically significant NPNs and its corresponding percentages?
1) Urea: 45% 2) Uric acid: 20% 3) Creatinine: 20% 4) Ammonia: 0.2% 5) Amino acid: 20% 6) Creatine: 1 - 2%
What is urea?
It is the major end-product of protein and AA metabolism (from ammonia and amino acid)
What are the characteristics of urea?
1) 45% most abundant of NPN; 80% total nitrogen excreted 2) Sensitive but not sp method for renal disorder
Where does the conversion from ammonia to urea happen?
It takes place in the liver
What are the sx considerations for BUN testing?
1) Non-fasting 2) Serum, plasma, whole blood, urine 3) Fluoride and citrate will inhibit urease 4) Avoid bacterial contamination in urine 5) Should be refrigerated when not analyzed immediately
What are the 2 methods for BUN testing?
1) Chemical method 2) Enzymatic method
What is chemical method?
It is the direct method
What enzyme is used for chemical method?
Diacetyl monoxime (DAM)
What is the principle of chemical method for BUN testing?
Urea + DAM = Yellow diazine derivative
What are the enzymes used for enzymatic method?
1) Urease 2) Glutamic dehydrogenase (GLDH)
What is the principle of rxn of enzymatic method?
Urea + H2O (via the action of urease) -> 2NH3^+ + CO2 2-Oxoglutarate + NH3^+ + NADH + H^+ (via the action of GLDH) -> L-Glutamate + NAD^+ + H2O
What should be done to BUN working rgnt?
Reconstitute using 12 mL distilled H2O
What is the amt of distilled H2O to be used for reconstitution of BUN working rgnt?
12 mL distilled H2O
True or False Urea nitrogen std is ready to use
True, because the urea nitrogen std is in liquid form
What are the mats needed for BUN testing?
1) Spectrophotometer 2) Distilled H2O 3) Semi-automated machine 4) Constant temp block or bath (H2O bath) 37 DC, or temp controlled cuvette 5) Accurate pipetting devices 6) Test tubes and rack 7) Timer
What is the procedure (or steps) for spectrophotometry (for BUN testing)?
1) Prepare BUN working rgnt accdg to instructions 2) Pipette 1,000 uL working rgnt into tubes labeled “standard”, “control”, “patient” 3) Add 10 uL of sx and mix 4) After exactly 30 secs, read and record absorbance (A1). At exactly 60 secs after reading (A1), read and record absorbance (A2) 5) Calculate change in absorbance (ΔA= A2 − A1) per min