Non-Protein Nitrogen

Question 1

Non-protein nitrogen sources

Answer 1

• urea
• amino acids
• uric acid
• creatinine
• ammonia

Question 2

Blood Urea Nitrogen (BUN)

Answer 2

• ammonia from the breakdown of protein
• urea formed in liver from ammonia (high NH4 levels cause brain damage)
• urea is main NPN compound
• filtered by renal tubules and partially reabsorped
• excreted by kidneys in urine

Question 3

BUN concentration

Answer 3

• depends on renal function, perfusion of kidney, protein content of diet and rate of protein catabolism
• increases with kidney damage because it can’t leave kidney
• decreases in people who don’t eat protein

Question 4

Azotemia

Answer 4

• increased BUN related to BUN abnormalities

- Pre-renal, Renal or Post-renal conditions

Question 5

Pre-renal conditions

Answer 5

• increased protein degradation (increase AA’s) due to diet, stress, fever, cortisol
• decreased blood flow thru kidney due to CHF, shock, hemmorrhage, dehydration, etc.

Question 6

Renal conditions

Answer 6

• kidney diseases, inflammation

- ineffective filtering by kidney

Question 7

Post-renal conditions

Answer 7

• blockages, obstructions
• calculi or severe kidney infection
• bladder or prostate tumor that blocks tubules

Question 8

BUN decreases

Answer 8

• not very often/significant
• low protein intake
• severe liver disease
• late in pregnancy, infancy (making more protein)

Question 9

BUN:Creatinine

Answer 9

• normal ratio is 10-20
• pre-renal: increased (elevated BUN, normal creatinine)
• renal: normal (both elevated but ratio is normal)
• post-renal: increased (both elevated, but especially BUN)
• low-protein diet: decreased (BUN low compared to creatinine)

Question 10

Methods for BUN analysis

Answer 10

• Coupled enzymatic method

- Electrochemical method

Question 11

Coupled enzymatic method

Answer 11

• NAD is one product of reaction

- NAD is measured at 340nm to get the BUN concentration

Question 12

Electrochemical method

Answer 12

• urease breaks down urea to ammonia
• ammonia ions change conductivity of electrode
• meter reads change in potential between standard and patient sample

Question 13

BUN specimens

Answer 13

• no ammonia, Na-citrate, Na-fluoride in samples
• don’t need fasting specimen
• avoid contamination
• plasma or serum, urine needs to be diluted

Question 14

Uric acid

Answer 14

• product of purine (A,G) breakdown
• secreted through kidney tubule, but 98% reabsorbed
• 70% excreted by kidneys, 30% by GI (of the 2%)

Question 15

Hyperuricemia

Answer 15

• Gout (inflammation of joints by uric acid crystals)
• increased in leukemia, G-6-PD deficiency, F-1-PA, Lactic acidosis
• Lesch-Nyhan syndrome (defect in HGPRT - enzyme that breaks down amino acids for recycling)
• chronic renal disease

Question 16

Hypouricemia

Answer 16

• Fanconi’s syndrome (tubule defect, don’t reabsorb uric acid)
• severe liver disease
• drugs (interfere with degradation)

Question 17

Methods for Uric Acid

Answer 17

• Enzymatic method
• uses uricase, produces peroxide
• use peroxidase + dye to make a color rxn

Question 18

Uric acid specimens

Answer 18

• heparinized plasma or serum

- NO EDTA

Question 19

High uric acid values can result from method susceptibility to

Answer 19

drugs like aspirin and thiazides

Question 20

Low uric acid value can result from method susceptibility to

Answer 20

• gross lipemia, high bilirubin, hemolysis, glutathione release
• interfere with perioxidase
• lipemia interferes with absorbance

Question 21

Creatinine

Answer 21

• produced from creatine degradation (in muscle tissue)
• levels depend on muscle mass
• plasma creatinine is inversely proportional to GFR
• filtered by kidney, some reabsorbed, some excreted in urine
• Creatinine Clearance is a measure of GFR

Question 22

eGFR

Answer 22

measure of GFR that accounts for age, gender and ethnicity

Question 23

High Creatinine Levels associated with

Answer 23

• decreased GFR
• not sensitive enough to predict glomerulus damage until 50% kidney loss
• can be due to high protein diet

Question 24

Creatinine methods

Answer 24

• Kinetic Jaffe rxn
• Colorimetric Jaffe rxn
• enzymatic method (with creatininase)
• Isotope Dilution Mass Spectroscopy (IDMS)

Question 25

Creatinine specimens

Answer 25

• plasma, serum, urine
• no hemolysis, lipemia, or icteric specimens
• fasting not required
• refrigerate urine

Question 26

Creatinine sources of error

Answer 26

• ascorbate, glucose, alpha-keto acids and uric acid
• bilirubin gives negative bias in rxns
• ascorbate and peroxidase rxns
• cephalosporin antibiotics
• dopamine and lidocaine

Question 27

Ammonia

Answer 27

• formed form the deamination of amino acids
• most processed into urea by liver, but some travels through blood and is excreted by the kidneys
• levels increase in liver failure, Reye’s syndrome and enzyme deficiencies in the urea cycle
• neurotoxic: can lead to encephalopathy

Question 28

Ammonia methods

Answer 28

• ion-selective electrode (measures pH change)

- enzymatic method (read absorbance)

Question 29

Ammonia specimens

Answer 29

• heparin or EDTA tube
• no hemolysis
• no smoking before specimen collection
• higher levels in kids