Blood Urea Nitrogen (BUN | F)

Question 1

What are the functions of kidney (including its corresponding mechanisms)?

Answer 1

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

Question 2

Excess H2O and toxic waste are excreted in the form of what?

Answer 2

Urine

Question 3

What are the roles of the kidney?

Answer 3

1) Excretion
2) Homeostasis
3) Osmoregulation
4) Regulation of salts in the body
5) Regulation of pH
6) Production of a hormone (EPO)

Question 4

What is the meaning of NPN?

Answer 4

Non-protein nitrogen

Question 5

What is an NPN?

Answer 5

It is the major substance excreted by the kidneys

Question 6

What is azotemia?

Answer 6

Elevated NPNs in the blood

Question 7

What is elevated if the pt has azotemia?

Answer 7

Urea

Question 8

What is uremia?

Answer 8

Azotemia + acidosis + electrolyte imbalance (hyperkalemia)

Question 9

What are the clinically significant NPNs and its corresponding percentages?

Answer 9

1) Urea: 45%
2) Uric acid: 20%
3) Creatinine: 20%
4) Ammonia: 0.2%
5) Amino acid: 20%
6) Creatine: 1 - 2%

Question 10

What is urea?

Answer 10

It is the major end-product of protein and AA metabolism (from ammonia and amino acid)

Question 11

What are the characteristics of urea?

Answer 11

1) 45% most abundant of NPN; 80% total nitrogen excreted

2) Sensitive but not sp method for renal disorder

Question 12

Where does the conversion from ammonia to urea happen?

Answer 12

It takes place in the liver

Question 13

What are the sx considerations for BUN testing?

Answer 13

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

Question 14

What are the 2 methods for BUN testing?

Answer 14

1) Chemical method

2) Enzymatic method

Question 15

What is chemical method?

Answer 15

It is the direct method

Question 16

What enzyme is used for chemical method?

Answer 16

Diacetyl monoxime (DAM)

Question 17

What is the principle of chemical method for BUN testing?

Answer 17

Urea + DAM = Yellow diazine derivative

Question 18

What are the enzymes used for enzymatic method?

Answer 18

1) Urease

2) Glutamic dehydrogenase (GLDH)

Question 19

What is the principle of rxn of enzymatic method?

Answer 19

Urea + H2O (via the action of urease) -> 2NH3^+ + CO2

2-Oxoglutarate + NH3^+ + NADH + H^+ (via the action of GLDH) -> L-Glutamate + NAD^+ + H2O

Question 20

What should be done to BUN working rgnt?

Answer 20

Reconstitute using 12 mL distilled H2O

Question 21

What is the amt of distilled H2O to be used for reconstitution of BUN working rgnt?

Answer 21

12 mL distilled H2O

Question 22

True or False

Urea nitrogen std is ready to use

Answer 22

True, because the urea nitrogen std is in liquid form

Question 23

What are the mats needed for BUN testing?

Answer 23

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

Question 24

What is the procedure (or steps) for spectrophotometry (for BUN testing)?

Answer 24

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

Question 25

What is the procedure (or steps) if chemistry machine is used (for BUN testing)?

Answer 25

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 2 mins, feed onto the machine
5) Analyze and record your results

Question 26

What is the normal reference range (for BUN testing)?

Answer 26

8 - 23 mg/dL

Question 27

What are the causes of increased BUN?

Answer 27

1) Chronic renal disease
2) Stress
3) Burns
4) High protein diet
5) Dehydration

Question 28

What are the causes of decreased BUN?

Answer 28

1) Poor nutrition
2) Hepatic disease
3) Impaired absorption
4) Pregnancy