Chemistry 6.4 Creatinine, Uric Acid, BUN, and Ammonia

Question 1

Creatinine is formed from the:
A. Oxidation of creatine
B. Oxidation of protein
C. Deamination of dibasic amino acids
D. Metabolism of purines

Answer 1

A. Oxidation of creatine

Question 2

Creatinine is considered one of the substances of choice to measure endogenous renal clearance because:
A. The rate of formation per day is independent of body size
B. It is completely filtered by the glomeruli
C. Plasma levels are highly dependent upon diet
D. Clearance is the same for both men and women

Answer 2

B. It is completely filtered by the glomeruli

Question 3

Which statement regarding creatinine is true?
A. Serum levels are elevated in early renal disease
B. High serum levels result from reduced glomerular filtration
C. Serum creatine has the same diagnostic utility as serum creatinine
D. Serum creatinine is a more sensitive measure of renal function than creatinine clearance

Answer 3

B. High serum levels result from reduced glomerular filtration

Question 4

Which of the following formulas is the correct expression for creatinine clearance?
A. Creatinine clearance = U/P × V × 1.73/A
B. Creatinine clearance = P/V × U × A/1.73
C. Creatinine clearance = P/V × U × 1.73/A
D. Creatinine clearance = U/V × P × 1.73/A

Answer 4

A. Creatinine clearance = U/P × V × 1.73/A

Question 5

Which of the following conditions is most likely to cause a falsely high creatinine clearance result?
A. The patient uses the midstream voiding procedure when collecting his or her urine
B. The patient adds tap water to the urine container because he or she forgets to save one of the urine samples
C. The patient does not empty his or her bladder at the conclusion of the test
D. The patient empties his or her bladder at the start of the test and adds the urine to the collection

Answer 5

D. The patient empties his or her bladder at the start of the test and adds the urine to the collection

Question 6

The modification of diet in renal disease (MDRD) formula for calculating estimated glomerular filtration rate (eGFR) requires which four parameters?
A. Urine creatinine, serum creatinine, height, weight
B. Serum creatinine, age, gender, race
C. Serum creatinine, height, weight, age
D. Urine creatinine, gender, weight, age

Answer 6

B. Serum creatinine, age, gender, race

Question 7

What substance may be measured as an alternative to creatinine for evaluating GFR?
A. Plasma urea
B. Cystatin C
C. Uric acid
D. Potassium

Answer 7

B. Cystatin C

Question 8

Which of the following enzymes allows creatinine to be measured by coupling to a peroxidase reaction?
A. Glucose-6-phosphate dehydrogenase
B. Creatinine deaminase
C. Sarcosine oxidase
D. Creatine kinase (CK)

Answer 8

C. Sarcosine oxidase

Question 9

Select the primary reagent used in the Jaffe method for creatinine.
A. Alkaline copper II sulfate
B. Saturated picric acid and sodium hydroxide (NaOH)
C. Sodium nitroprusside and phenol
D. Phosphotungstic acid

Answer 9

B. Saturated picric acid and sodium hydroxide (NaOH)

Question 10

Interference from other reducing substances can be partially eliminated in the Jaffe reaction by:
A. Measuring the product at 340 nm
B. Measuring the product with an electrode
C. Measuring the timed rate of product formation
D. Performing a sample blank

Answer 10

C. Measuring the timed rate of product formation

Question 11

Which of the following statements is true?
A. Cystatin C is measured immunochemically
B. The calibrator used for cystatin C is traceable to the National Bureau of Standards calibrator
C. Cystatin C assays have a lower coefficient of variation compared with plasma creatinine
D. Enzymatic and rate Jaffe reactions for creatinine give comparable results

Answer 11

A. Cystatin C is measured immunochemically

Question 12

In which case would eGFR derived from the plasma creatinine likely give a more accurate measurement of GFR compared with measurement of plasma cystatin C?
A. Diabetes
B. Chronic renal failure
C. After renal transplantation
D. Chronic hepatitis

Answer 12

C. After renal transplantation

Question 13

A sample of amniotic fluid collected for fetal lung maturity studies from a woman whose pregnancy was compromised by hemolytic disease of the fetus and newborn (HDFN) has a creatinine level of 88 mg/dL. What is the most likely cause of this result?
A. The specimen is contaminated by blood
B. Bilirubin has interfered with the measurement of creatinine
C. A random error occurred when the absorbance signal was being processed by the analyzer
D. The fluid is urine from accidental puncture of the urinary bladder

Answer 13

D. The fluid is urine from accidental puncture of the urinary bladder

Question 14

Which analyte should be reported as a ratio using creatinine concentration as a reference?
A. Urinary microalbumin
B. Urinary estriol
C. Urinary sodium
D. Urinary urea

Answer 14

A. Urinary microalbumin

Question 15

Urea is produced from:
A. The catabolism of proteins and amino acids
B. Oxidation of purines
C. Oxidation of pyrimidines
D. The breakdown of complex carbohydrates

Answer 15

A. The catabolism of proteins and amino acids

Question 16

Urea concentration is calculated from the BUN by multiplying by a factor of:
A. 0.5
B. 2.14
C. 6.45
D. 14

Answer 16

B. 2.14

BUN is multiplied by 2.14 to give the urea concentration in mg/dL.

BUN (mg/dL) = urea × (%N in urea ÷ 100)
Urea = BUN × 1/(%N in urea ÷ 100)
Urea = BUN × (1/0.467) = 2.14

Question 17

Which of the statements below about serum urea is true?
A. The levels are independent of diet
B. Urea is not reabsorbed by the renal tubules
C. High BUN levels can result from necrotic liver disease
D. BUN is elevated in prerenal as well as renal failure

Answer 17

D. BUN is elevated in prerenal as well as renal failure

Question 18

A patient’s BUN is 60 mg/dL and serum creatinine is 3.0 mg/dL. These results suggest:
A. Laboratory error measuring BUN
B. Renal failure
C. Prerenal failure
D. Patient was not fasting

Answer 18

C. Prerenal failure

Question 19

Urinary urea measurements may be used for calculation of:
A. Glomerular filtration
B. Renal blood flow
C. Nitrogen balance
D. All of these options

Answer 19

C. Nitrogen balance

Question 20

BUN is determined electrochemically by coupling the urease reaction to the measurement of:
A. H2O2
B. The timed rate of increase in conductivity
C. The oxidation of ammonia
D. CO2

Answer 20

B. The timed rate of increase in conductivity

Question 21

In the ultraviolet enzymatic method for BUN, the urease reaction is coupled to a second enzymatic reaction using:
A. Aspartate aminotransferase (AST)
B. Glutamate dehydrogenase (GLD)
C. Glutamine synthetase
D. Alanine aminotransferase (ALT)

Answer 21

B. Glutamate dehydrogenase (GLD)

Question 22

Which product is measured in the coupling step of the urease-UV method for BUN?
A. CO2
B. Dinitrophenylhydrazine
C. Diphenylcarbazone
D. NAD+

Answer 22

D. NAD+

Question 23

Which enzyme deficiency is responsible for phenylketonuria (PKU)?
A. Phenylalanine hydroxylase
B. Tyrosine transaminase
C. p-Hydroxyphenylpyruvic acid oxidase
D. Homogentisic acid oxidase

Answer 23

A. Phenylalanine hydroxylase

Question 24

Which of the following conditions is classified as a renal-type aminoaciduria?
A. Fanconi syndrome
B. Wilson disease
C. Hepatitis
D. Homocystinuria

Answer 24

A. Fanconi syndrome

Question 25

Which aminoaciduria results in the overflow of branched chain amino acids?
A. Hartnup disease
B. Alkaptonuria
C. Homocystinuria
D. Maple syrup urine disease

Answer 25

D. Maple syrup urine disease

Question 26

In addition to phenylketonuria, maple syrup urine disease, and homocystinuria, what other aminoaciduria can be detected by MS/MS?
A. Alkaptonuria
B. Hartnup disease
C. Citrullinemia
D. Cystinuria

Answer 26

C. Citrullinemia

Question 27

Of the methods used to measure amino acids, which is capable of measuring fatty acids simultaneously?
A. MS/MS
B. HPLC
C. Capillary electrophoresis
D. Two-dimensional TLC

Answer 27

A. MS/MS

Question 28

Blood ammonia levels are usually measured to evaluate:
A. Renal failure
B. Acid–base status
C. Hepatic coma
D. GI malabsorption

Answer 28

C. Hepatic coma

Question 29

Enzymatic measurement of ammonia requires which of the following substrates and coenzymes?
A. 2-oxogluterate/NADH
B. Glutamate/NADH
C. Glutamine/ATP
D. Glutamine/NAD+

Answer 29

A. 2-oxogluterate/NADH

Question 30

Which statement about ammonia is true?
A. Normally, most of the plasma ammonia is derived from peripheral blood deamination of amino acids
B. Ammonia-induced coma can result from salicylate poisoning
C. Hepatic coma can result from Reye syndrome
D. High plasma ammonia is usually caused by respiratory alkalosis

Answer 30

C. Hepatic coma can result from Reye syndrome

Question 31

SITUATION: A sample for ammonia assay is taken from an IV line that had been capped and injected with lithium heparin (called a heparin lock). The sample is drawn in a syringe containing lithium heparin and immediately capped and iced. The plasma is separated and analyzed within 20 minutes of collection, and the result is 50 µg/dL higher than one measured 4 hours before. What is the most likely explanation of these results?

A. Significantly greater physiological variation is seen with patients with systemic, hepatic, and GI diseases
B. The syringe was contaminated with ammonia
C. One of the two samples was collected from the wrong patient
D. Stasis of blood in the line caused increased ammonia

Answer 31

D. Stasis of blood in the line caused increased ammonia

Question 32

Uric acid is derived from:
A. Oxidation of proteins
B. Catabolism of purines
C. Oxidation of pyrimidines
D. Reduction of catecholamines

Answer 32

B. Catabolism of purines

Question 33

Which of the following conditions is associated with hyperuricemia?
A. Renal failure
B. Chronic liver disease
C. Xanthine oxidase deficiency
D. Paget disease of the bone

Answer 33

A. Renal failure

Question 34

Orders for uric acid are legitimate stat requests because:
A. Levels above 10 mg/dL cause urinary tract calculi
B. Uric acid is hepatotoxic
C. High levels induce aplastic anemia
D. High levels cause joint pain

Answer 34

A. Levels above 10 mg/dL cause urinary tract calculi

Question 35

Which uric acid method is associated with negative bias caused by reducing agents?
A. Uricase coupled to the Trinder reaction
B. UV uricase reaction coupled to catalase and alcohol dehydrogenase (ADH) reactions
C. Measurement of the rate of absorbance decrease at 290 nm after addition of uricase
D. Amperometry

Answer 35

A. Uricase coupled to the Trinder reaction