Clinical Chemistry- Creatinine, Uric Acid, BUN, and Ammonia

Question 1

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

2. Creatinine is considered the substance 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

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

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

Answer 4

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

Question 5

5. Which of the following conditions is most likely to
   cause a falsely high creatinine clearance result?
   A. The patient uses the midstream void 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

6. The modification of diet in renal disease (MDRD)
   formula for calculating 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

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

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

Answer 8

C. Sarcosine oxidase

Question 9

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

Answer 9

B. Saturated picric acid and NaOH

Question 10

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

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 than plasma creatinine
    D. Enzymatic and rate Jaffe reactions for creatinine
    give comparable results

Answer 11

A. Cystatin C is measured immunochemically

Question 12

12. In which case would eGFR derived from the
    plasma creatinine likely give a more accurate
    measure of GFR than measurement of plasma
    cystatin C?
    A. Diabetic patient
    B. Chronic renal failure
    C. Post–renal transplant
    D. Chronic hepatitis

Answer 12

C. Post–renal transplant

Question 13

13. A sample of amniotic fluid collected for fetal lung
    maturity studies from a woman with a pregnancy
    compromised by hemolytic disease of the newborn
    (HDN) has a creatinine of 88 mg/dL. What is the
    most likely cause of this result?
    A. The specimen is contaminated with 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

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

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

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

Question 17

17. Which of the statements below about serum urea
    is true?
    A. 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

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

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

20. BUN is determined electrochemically by coupling
    the urease reaction to measurement of:
    A. Potential with a urea-selective electrode
    B. The timed rate of increase in conductivity
    C. The oxidation of ammonia
    D. Carbon dioxide

Answer 20

B. The timed rate of increase in conductivity

Question 21

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

Answer 21

B. Glutamate dehydrogenase

Question 22

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

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

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

Answer 24

A. Fanconi syndrome

Question 25

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

Answer 25

D. Maple syrup urine disease

Question 26

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

Answer 26

C. Citrullinemia

Question 27

27. Of the methods used to measure amino acids,
    which is capable of measuring fatty acids
    simultaneously?
    A. Tandem-mass spectroscopy
    B. High-performance liquid chromatography
    C. Capillary electrophoresis
    D. Two-dimensional thin-layer chromatography

Answer 27

A. Tandem-mass spectroscopy

Question 28

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

Answer 28

C. Hepatic coma

Question 29

29. Enzymatic measurement of ammonia requires
    which of the following substrates and coenzymes?

Answer 29

A.

Question 30

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’s syndrome
    D. High plasma ammonia is usually caused by
    respiratory alkalosis

Answer 30

C. Hepatic coma can result from Reye’s syndrome

Question 31

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 having systemic, hepatic, and
    gastrointestinal 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

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

Answer 32

B. Catabolism of purines

Question 33

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

Answer 33

A. Renal failure

Question 34

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

35. Which uric acid method is associated with
    negative bias caused by reducing agents?
    A. Uricase coupled to the Trinder reaction
    B. Ultraviolet uricase reaction coupled to catalase
    and alcohol dehydrogenase reactions
    C. Measurement of the rate of absorbance decrease
    at 290 nm after addition of uricase
    D. Phosphotungstic acid using a protein-free filtrate

Answer 35

A. Uricase coupled to the Trinder reaction