Clinical Chemistry (Enzymes and Cardiac Assessment)

Question 1

What does an increase in the serum enzyme levels indicate?

A. Decreased enzyme catabolism
B. Accelerated enzyme production
C. Tissue damage and necrosis
D. Increased glomerular filtration rate

Question 2

In the assay of an enzyme, zero-order kinetics are best described by which of the following statements?

A. Enzyme is present in excess; rate of reaction is variable with time and dependent only on the concentration of the enzyme in the system.
B. Substrate is present in excess; rate of reaction is constant with time and dependent only on the concentration of enzyme in the system.
C. Substrate is present in excess; rate of reaction is constant with enzyme concentration and dependent only on the time in which the reaction is run.
D. Enzyme is present in excess; rate of reaction is independent of both time and concentration of the enzyme in the system.

Question 3

Based on the following graph of velocity of an enzyme reaction versus substrate concentration, you are designing a new method to measure the activity of an enzyme of clinical interest. To formulate the new methodology so that enzyme activity is assessed using zero-order kinetics, which concentration of substrate should you initially determine experimentally?

Michaelis-Menten Curve
|
vmax| _____________________
| /
1/2 vmax|–/
|/_______________________

A. Substrate concentration a
B. Substrate concentration b
C. Substrate concentration c
D. Substrate concentration d

Question 4

When measuring enzyme activity, if the
instrument is operating 5°C lower than the
temperature prescribed for the method,
how will the results be affected?

A. Lower than expected
B. Higher than expected
C. Varied, showing no particular pattern
D. All will be clinically abnormal.

Question 5

Given the following information for a rate
reaction, calculate the activity of a serum
specimen for alanine aminotransferase in
international units per liter (IU/L).

Time Absorbance
1 min 1.104
2 min 1.025
3 min 0.950
4 min 0.873

Specimen volume = 20 uL
Reagent volume = 3.0 mL
Molar absorptivity for NADH at 340 nm = 6.22 x 10^3 L/mol*cm
Light path = 1 cm

A. 186
B. 198
C. 1857
D. 1869

Question 6

The properties of enzymes are correctly described by which of the following statements?

A. Enzymes are stable proteins.
B. Enzymes are protein catalysts of biological origin.
C. Enzymes affect the rate of a chemical reaction by raising the activation energy needed for the reaction to take place.
D. Enzyme activity is not altered by heat denaturation.

Question 7

Which of the following is a true statement concerning serum enzymes?

A. The presence of hemolyzed red cells is of no significance for an accurate assay of most serum enzymes.
B. Serum asparate transaminase (AST), but not serum lactate dehydrogenase (LD), is usually elevated in acute myocardial infarction.
C. Increased serum alkaline phosphatase may be found in bone disease.
D. Aspartate transaminase was formerly known as glutamate pyruvate transaminase

Question 8

Enzymes that catalyze the transfer of groups between compounds are classified as belonging to which enzyme class?

A. Hydrolases
B. Eyases
C. Oxidoreductases
D. Transferases

Question 9

Which of the following enzymes does not belong to the class of enzymes known as the hydrolases?

A. Alkaline phosphatase
B. Aldolase
C. Amylase
D. Lipase

Question 10

To what class of enzymes does lactate dehydrogenase belong?

A. Isomerases
B. Ligases
C. Oxidoreductases
D. Transferases

Question 11

Which of the following enzymes catalyzes the transfer of amino groups causing the interconversion of amino acids and a- oxoacids?

A. Amylase
B. Aspartate transaminase
C. Alkaline phosphatase
D. Lactate dehydrogenase

Question 12

What abbreviation has been used in the past to designate alanine aminotransferase?

A. AST
B. AAT
C. GOT
D. GPT

Question 13

When measuring CK-MB, which of the following would provide the most sensitive method?

A. Electrophoretic
B. Colorimetric
C. Kinetic
D. Mass immunoassay

Question 14

Which of the following does not accurately describe properties associated with lactate dehydrogenase?

A. Optimum pH for the catalysis of lactate to pyruvate is 7.4-7.8.
B. LD is increased in a hemolyzed serum specimen.
C. LD catalyzes the oxidation of lactate to pyruvate with mediation of nicotinamide-adenine dinucleotide.
D. LD-4 and LD-5 are labile in the cold

Question 15

Which test, if elevated, would provide information about risk for developing coronary artery disease?

A. Troponin
B. CK-MB
C. hs-CRP
D. Myoglobin

Question 16

Lactate dehydrogenase (LD) catalyzes the following reaction:

Lactate + NAD+ ⇌ (LD) ⇌ pyruvate + NADH

As the reaction is written, which of the following techniques can be used to assess LD activity?

A. Measure the colorimetric product pyruvate.
B. Measure the colorimetric product NADH.
C. Measure the increase in absorbance at 340 nm as NADH is produced.
D. Measure the decrease in absorbance at 340 nm as NADH is produced.

Question 17

Which of the following is false about myoglobin as it relates to acute myocardial infarction (AMI)?

A. Measure serially
B. Cardiac specific
C. Initial increase occurs in 1-3 hours
D. Doubling of initial value within
1-2 hours suggestive of AMI

Question 18

Which of the following disorders is not associated with an elevation of serum creatine kinase?

A. Cerebrovascular accidents
B. Hypothyroidism
C. Bone disease
D. Intramuscular injection

Question 19

Which of the following statements concerning creatine kinase is false?

A. Rises within 4-6 hours after acute myocardial infarction
B. Catalyzes the phosphorylation of creatine by ATP
C. Requires Ca2+ for activity
D. Found mainly in skeletal and cardiac
muscles and in brain tissue

Question 20

Which enzyme is measured by methodologies that use small oligosaccharides and 4-nitrophenyl-glycoside for substrates?
A. Lipase
B. Amylase
C. Creatine kinase
D. Cholinesterase

Question 21

Which statement concerning gammaglutamyltransferase is false?

A. Present in almost all cells of the body
B. Elevated in liver and some pancreatic
diseases
C. Elevated in chronic alcoholism
D. Elevated in bone disease

Question 22

Which of the following statements correctly describes alkaline phosphatase?

A. Decreased in Paget disease
B. Decreased in third trimester of a normal pregnancy
C. Increased in obstructive jaundice
D. Primarily found in cardiac muscle

Question 23

Which of the following enzymes would not be useful to quantify in the assessment of liver function?

A. Alanine aminotransferase
B. Creatine kinase
C. Alkaline phosphatase
D. Gamma-glutamyltransferase

Question 24

In acute pancreatitis, a significant increase in which serum enzyme would be expected diagnostically?

A. Creatine kinase
B. Amylase
C. Alkaline phosphatase
D. Aspartate aminotransferase

Question 25

For assessing carcinoma of the prostate, quantification of PSA has virtually replaced the measurement of which of the following enzymes?

A. Alkaline phosphatase
B. Acid phosphatase
C. Alanine aminotransferase
D. Trypsin

Question 26

Which of the following statements is not associated with serum cholinesterase?

A. Inhibited by organic insecticides
B. Referred to as “true” cholinesterase
C. Decreased level causes prolonged apnea after administration of succinyldicholine
D. Acts on the substrate propionylthiocholine

Question 27

Which of the following disorders is not characterized by an elevated serum myoglobin?

A. Renal failure
B. Vigorous exercise
C. Acute myocardial infarction
D. Hepatitis

Question 28

Which of the following is false about cardiac troponin I (cTnl) as it relates to AMI?

A. Increase above reference interval seen in 3 to 6 hours
B. Measure initially and serially in 3- to 6-hour intervals
C. Remains elevated 5 to 10 days
D. Expressed in regenerating and diseased skeletal muscle and cardiac muscle disorders

Question 29

Which of the following sets of tests would be the most useful in diagnosing an AMI?

A. AST, LD, CK-MB
B. LD, CK-MB, troponin
C. CK-MB, troponin, myoglobin
D. LD, troponin, myoglobin

Question 30

A physician orders several laboratory tests on a 55-year-old male patient who is complaining of pain, stiffness, fatigue, and headaches. Based on the following serum test results, what is the most likely diagnosis?
Alkaline phosphatase—significantly increased
Gamma-glutamyltransferase—normal

A. Biliary obstruction
B. Cirrhosis
C. Hepatitis
D. Osteitis deformans

Question 31

A 53-year-old female presents with fatigue, pruritus, and an enlarged, nontender liver. The physician orders a series of blood tests. Based on the following serum test results, what is the most likely diagnosis?

Alkaline phosphatase—markedly elevated
Alanine aminotransferase—slightly elevated
Lactate dehydrogenase—slightly elevated
Gamma-glutamyltransferase— markedly elevated
Total bilirubin—slightly elevated

A. Alcoholic cirrhosis
B. Infectious mononucleosis
C. Intrahepatic cholestasis
D. Viral hepatitis

Question 32

A 42-year-old male presents with anorexia, nausea, fever, and icterus of the skin and mucous membranes. He noticed that his urine had appeared dark for the past several days. The physician orders a series of biochemical tests. Based on the following test results, what is the most likely diagnosis?

Serum alkaline phosphatase—slightly elevated
Serum alanine aminotransferase— markedly elevated
Serum aspartate aminotransferase—markedly elevated
Serum gamma-glutamyltransferase— slightly elevated
Serum total bilirubin—moderately elevated
Urine bilirubin—positive
Fecal urobilinogen—decreased

A. Acute hepatitis
B. Alcoholic cirrhosis
C. Metastatic carcinoma of the pancreas
D. Obstructive jaundice

Question 33

To aid in the diagnosis of skeletal muscle disease, which of the following serum enzyme measurements would be of most use?

A. Creatine kinase
B. Alkaline phosphatase
C. Aspartate aminotransferase
D. Alanine aminotransferase

Question 34

When an AMI occurs, in what order (list first to last) will the enzymes aspartate aminotransferase (AST), creatine kinase (CK), and lactate dehydrogenase (LD) become elevated in the serum?

A. AST, LD, CK
B. CK,LD,AST
C. CK,AST, LD
D. LD, CK,AST

Question 35

Which of the following is not associated with assessment of an AMI?

A. Elevated serum cTnl level
B. Elevated serum CK-MB level
C. Abnormal serum alkaline phosphatase isoenzyme pattern
D. Blood collected upon presentation and serially in 3- to 6-hour intervals

Question 36

If elevated, which laboratory test would support a diagnosis of congestive heart failure?

A. Homocysteine
B. Troponin
C. Albumin cobalt binding
D. B-type natriuretic peptide

Question 37

A 4-year-old male child is brought to the pediatrician because the parents are concerned about the child’s frequent falling, which results in bruising. The parents indicate that the child has difficulty running, walking, standing up, climbing stairs, and even sitting up straight. The child also appears somewhat weak. Which of the following results is not consistent with the most likely diagnosis?

A. Moderately elevated AST
B. Moderately elevated ALP
C. Moderately elevated LD
D. Markedly elevated CK

Question 38

A 68-year-old male in an unconscious state is transported to the emergency department after being involved in a one-car crash, where he drove off the road and hit a tree. Because he was alone at the time and there was no apparent cause for the accident, it is assumed that he blacked out, which caused him to lose control of the car. He was not wearing a seat belt and has a broken leg, multiple contusions, and cuts. Blood samples were drawn upon arrival to the ED and in 3-hour intervals for 12 hours; all control values were within acceptable range. Selected test results follow:

Test Initial Values 3 Hours 9 Hours
Myoglobin 57 ng/mL 140 ng/mL 281 ng/mL
Total CK 112 U/L 170 U/L 390 U/L
CK-MB 3 ng/mL 6 ng/mL 8 ng/mL
Troponin I 0.10 ng/mL 0.12 ng/mL 0.11ng/mL

Reference range:
Myoglobin : 30-90 ng/mL
Total CK : 15-160 U/L
CK-MB : 0-5 ng/mL
Troponin I : <0.40 ng/mL

What do these test results suggest?

A. The man had a myocardial infarction, which caused the accident.
B. The elevated results are from the skeletal muscle injuries sustained in the car crash.
C. The elevated results are a combination of the car crash injuries and a myocardial infarction.
D. The elevated total CK and CK-MB results indicate that the man had a stroke

Question 39

If elevated, which of the following is associated with increased risk for coronary heart disease?

A. Homocysteine
B. Vitamin B6
C. Myoglobin
D. pro-BNP

Question 40

Which statement best describes the clinical use of measuring NT-proBNP?

A. Used to assess risk of coronary heart disease
B. Used to assess risk of angina
C. Used to assess individuals treated with nesiritide
D. Used to assess individuals treated with vitamin B

Question 41

A 10-year-old female presents with varicella. The child has been experiencing fever, nausea, vomiting, lethargy, and disorientation. A diagnosis of Reye syndrome is determined. Which of the following laboratory results is not consistent with the diagnosis?

A. Elevated serum AST
B. Elevated serum ALT
C. Elevated plasma ammonia
D. Elevated serum bilirubin

Question 42

Which of the following enzyme activities can be determined by using a dilute olive oil emulsion substrate, whose hydrolyzed product is monitored as a decrease in turbidity or light scatter?

A. Alkaline phosphatase
B. Amylase
C. Lipase
D. Trypsin

Question 43

Which of the following is not characteristic of cystic fibrosis?

A. Decreased bicarbonate concentration in duodenal fluid
B. Decreased lipase activity in duodenal fluid
C. Decreased amylase activity in duodenal fluid
D. Increased trypsin in feces