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CC HARR > Enzymes and Cardiac Markers > Flashcards

Enzymes and Cardiac Markers Flashcards

1
Q

An international unit (IU) of enzyme activity is the quantity of enzyme that:
A. Converts 1 μmol of substrate to product per liter
B. Forms 1 mg of product per deciliter
C. Converts 1 μmol of substrate to product per minute
D. Forms 1 μmol of product per liter

A

C. Converts 1 μmol of substrate to product per minute

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2
Q

Which of the following statements describes a nonkinetic enzyme assay?
A. Initial absorbance is measured followed by a second reading after 5 minutes
B. Absorbance is measured at 10-second intervals
for 100 seconds
C. Absorbance is monitored continuously for
1 minute using a chart recorder
D. Reflectance is measured from a xenon source
lamp pulsing at 60 Hz

A

A. Initial absorbance is measured followed by a
second reading after 5 minutes

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3
Q

Which of the following statements regarding enzymatic reactions is true?
A. The enzyme shifts the equilibrium of the reaction
to the right
B. The enzyme alters the equilibrium constant of
the reaction
C. The enzyme increases the rate of the reaction
D. The enzyme alters the energy difference between reactants and products

A

C. The enzyme increases the rate of the reaction

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4
Q

Which statement about enzymes is true?
A. An enzyme alters the Gibb’s free energy of the
reaction
B. Enzymes cause a reaction with a positive free
energy to occur spontaneously
C. An enzyme’s natural substrate has the highest Km
D. A competitive inhibitor will alter the apparent Km of the reaction

A

D. A competitive inhibitor will alter the apparent Km of the reaction

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5
Q

Which of the following statements is true?
A. Apoenzyme + prosthetic group = holoenzyme
B. A coenzyme is an inorganic molecule required
for activity
C. Cofactors are as tightly bound to the enzyme as
prosthetic groups
D. All enzymes have optimal activity at pH 7.00

A

A. Apoenzyme + prosthetic group = holoenzyme

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6
Q

Which of the following statements about enzymatic reactions is true?
A. NADH has absorbance maximas at 340
and 366 nm
B. Enzyme concentration must be in excess to
achieve zero-order kinetics
C. Rate is proportional to substrate concentration in
a zero-order reaction
D. Accumulation of the product increases the
reaction rate

A

A. NADH has absorbance maximas at 340
and 366 nm

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7
Q

The increase in the level of serum enzymes used to detect cholestatic liver disease is caused mainly by: A. Enzyme release from dead cells
B. Leakage from cells with altered membrane
permeability
C. Decreased perfusion of the tissue
D. Increased production and secretion by cells

A

D. Increased production and secretion by cells

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8
Q

Which of the following enzymes is considered most tissue specific?
A. Creatine kinase (CK)
B. Amylase
C. Alkaline phosphatase (ALP)
D. Alcohol dehydrogenase (ADH)

A

D. Alcohol dehydrogenase (ADH)

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9
Q

Which of the following enzymes is a transferase?
A. ALP
B. CK
C. Amylase
D. LD

A

B. CK

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10
Q

Which statement about methods for measuring LD is true?
A. The formation of pyruvate from lactate (forward reaction) generates NAD+
B. The pyruvate-to-lactate reaction proceeds at about twice the rate as the forward reaction
C. The lactate-to-pyruvate reaction is optimized at pH 7.4
D. The negative-rate reaction is preferred

A

B. The pyruvate-to-lactate reaction proceeds at about twice the rate as the forward reaction

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11
Q

Which condition produces the highest elevation of serum lactate dehydrogenase?
A. Pernicious anemia
B. Myocardial infarction
C. Acute hepatitis
D. Muscular dystrophy

A

A. Pernicious anemia

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12
Q

In which condition is the LD most likely to be within normal limits?
A. Hepatic carcinoma
B. Pulmonary infarction
C. Acute appendicitis
D. Crush injury

A

C. Acute appendicitis

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13
Q

The LD pleural fluid:serum ratio for a transudative fluid is usually:
A. 3:1 or higher
B. 2:1
C. 1:1
D. 1:2 or less

A

D. 1:2 or less

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14
Q

In which type of liver disease would you expect the greatest elevation of LD?
A. Toxic hepatitis
B. Alcoholic hepatitis
C. Cirrhosis
D. Acute viral hepatitis

A

A. Toxic hepatitis

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15
Q

Which of the following conditions will interfere with the measurement of LD?
A. Slight hemolysis during sample collection
B. Storage at 4°C for 3 days
C. Storage at room temperature for 16 hours
D. Use of plasma collected in heparin

A

A. Slight hemolysis during sample collection

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16
Q

In the Oliver–Rosalki method, the reverse reaction is used to measure CK activity. The enzyme(s) used in the coupling reactions is (are):
A. Hexokinase and G-6-PD
B. Pyruvate kinase and LD
C. Luciferase
D. Adenylate kinase

A

A. Hexokinase and G-6-PD

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17
Q

In the Oliver–Rosalki method for CK, adenosine monophosphate (AMP) is added to the substrate in order to:
A. Inhibit adenylate kinase
B. Block the oxidation of glutathione
C. Increase the amount of ADP that is available
D. Block the action of diadenosine pentaphosphate

A

A. Inhibit adenylate kinase

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18
Q

Which substance is used in the CK assay to activate the enzyme?
A. Flavin adenine dinucleotide (FAD)
B. Imidazole
C. N-acetylcysteine
D. Pyridoxyl-5 ́-phosphate

A

C. N-acetylcysteine

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19
Q

SITUATION: A specimen for CK performed
on an automated analyzer using an optimized Oliver–Rosalki method gives an error flag indicating substrate depletion. The sample is diluted 1:2 and 1:4 by the serial dilution technique and reassayed. After correcting for the dilution, the results are as follows:

1:2 Dilution = 3,000 IU/L 1:4 Dilution = 3,600 IU/L

Dilutions are made a second time and assayed again but give identical results. What is the most likely explanation?

A. The serum became contaminated prior to
making the 1:4 dilution
B. The wrong pipet was used to make one of the
dilutions
C. An endogenous competitive inhibitor is present
in the serum
D. An error has been made in calculating the
enzyme activity of one of the two dilutions

A

C. An endogenous competitive inhibitor is present
in the serum

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20
Q

SITUATION: A physician calls to request a CK on a sample already sent to the laboratory for coagulation studies. The sample is 2-hour-old citrated blood and has been stored at 4°C. The plasma shows very slight hemolysis. What is the best course of action and the reason for it?
A. Perform the CK assay on the sample because no interferent is present
B. Reject the sample because it is slightly hemolyzed
C. Reject the sample because it has been stored
too long
D. Reject the sample because the citrate will
interfere

A

D. Reject the sample because the citrate will
interfere

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21
Q

Which of the following statements regarding total CK is true?
A. Levels are unaffected by strenuous exercise
B. Levels are unaffected by repeated intramuscular
injections
C. Highest levels are seen in Duchenne’s muscular
dystrophy
D. The enzyme is highly specific for heart injury

A

C. Highest levels are seen in Duchenne’s muscular
dystrophy

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22
Q

Which of the following statements regarding the clinical use of CK-MB (CK-2) is true?
A. CK-MB becomes elevated before myoglobin
after an AMI
B. CK-MB levels are usually increased in cases of
cardiac ischemia
C. CK-MB is more specific than myoglobin
D. An elevated CK-MB is always accompanied by an elevated total CK

A

C. CK-MB is more specific than myoglobin

23
Q

A patient’s CK-MB is reported as 18 μg/L and the total CK as 560 IU/L. What is the CK relative index (CKI)?
A. 0.10%
B. 3.2%
C. 10.0%
D. 30.0%

A

B. 3.2%

24
Q

In a nonmyocardial as opposed to a myocardial cause of an increased serum or plasma CK-MB, which would be expected?
A. An increase in CK-MB that is persistent
B. An increase in the percent CK-MB as well as concentration
C. The presence of increased TnI
D. A more modest increase in total CK than
CK-MB

A

A. An increase in CK-MB that is persistent

25
Q

Which statement best describes the clinical utility of plasma or serum myoglobin?
A. Levels greater than 100 μg/L are diagnostic
of AMI
B. Levels below 100 μg/L on admission and
2–4 hours postadmission help to exclude a
diagnosis of AMI
C. Myoglobin peaks after the cardiac troponins
but is more sensitive
D. The persistence of myoglobin > 110 μg/L for
3 days following chest pain favors a diagnosis of AMI

A

B. Levels below 100 μg/L on admission and
2–4 hours postadmission help to exclude a
diagnosis of AMI

26
Q

What is the typical time course for plasma myoglobin following an AMI?
A. Abnormal before 1 hour; peaks within 3 hours;
returns to normal in 8 hours
B. Abnormal within 3 hours; peaks within 6 hours;
returns to normal in 18 hours
C. Abnormal within 2 hours; peaks within
12 hours; returns to normal in 36 hours
D. Abnormal within 6 hours; peaks within
24 hours; returns to normal in 72 hours

A

C. Abnormal within 2 hours; peaks within
12 hours; returns to normal in 36 hours

27
Q

Which substrate concentration is needed to achieve zero-order conditions?
A. Greater than 99 × Km
B. [S] = Km
C. Less than 10 × Km
D. [S] = 0

A

A. Greater than 99 × Km

28
Q

What is the typical time course for plasma myoglobin following an AMI?
A. Abnormal before 1 hour; peaks within 3 hours;
returns to normal in 8 hours
B. Abnormal within 3 hours; peaks within 6 hours;
returns to normal in 18 hours
C. Abnormal within 2 hours; peaks within
12 hours; returns to normal in 36 hours
D. Abnormal within 6 hours; peaks within
24 hours; returns to normal in 72 hours

A

C. Abnormal within 2 hours; peaks within
12 hours; returns to normal in 36 hours

29
Q

What is the typical time course for plasma TnI or TnT following an AMI?
A. Abnormal within 3 hours; peaks within
12 hours; returns to normal in 24 hours
B. Abnormal within 4 hours; peaks within
18 hours; returns to normal in 48 hours
C. Abnormal within 4 hours; peaks within
24 hours; returns to normal in 1 week
D. Abnormal within 6 hours; peaks within
36 hours; returns to normal in 5 days

A

C. Abnormal within 4 hours; peaks within
24 hours; returns to normal in 1 week

30
Q

Which of the following is the most effective serial sampling time for ruling out AMI using both myoglobin and a cardiac specific marker in an emergency department environment?
A. Admission and every hour for the next 3 hours or until positive
B. Admission, 2 hours, 4 hours, and 6 hours or until positive
C. Admission, 3 hours, 6 hours, and a final sample within 12 hours
D. Admission and one sample every 8 hours for 48 hours

A

C. Admission, 3 hours, 6 hours, and a final sample within 12 hours

31
Q

What is the recommended troponin T and I cutoff (upper limit of normal) for detecting myocardial infarction?
A. The cutoff varies with the method of assay but
should be no lower than 0.2 ng/mL
B. The upper 99th percentile or lowest level that
can be measured with 10% CV
C. The concentration corresponding to the lowest
level of calibrator used
D. The highest value fitting under the area of the
curve for the 95% confidence interval

A

B. The upper 99th percentile or lowest level that
can be measured with 10% CV

32
Q

Which of the following cardiac markers is consistently increased in persons who exhibit unstable angina?
A. Troponin C
B. Troponin T
C. CK-MB
D. Myoglobin

A

B. Troponin T

33
Q

A patient has a plasma myoglobin of 10 μg/L at admission. Three hours later, the myoglobin is
14 μg/L and the troponin I is 0.02 μg/L (reference range 0–0.03 μg/L). These results are consistent with which condition?
A. Skeletal muscle injury
B. Acute myocardial infarction
C. Unstable angina
D. No evidence of myocardial or skeletal muscle injury

A

D. No evidence of myocardial or skeletal muscle injury

34
Q

A patient has a plasma CK-MB of 14 μg/L at admission and a total CK of 170 IU/L. Serum myoglobin is 130 μg/L and TnI is 1.6 μg/L. Three hours later, the TnI is 3.0 μg/L. Which statement best describes this situation?
A. This patient has had an AMI and further testing is unnecessary
B. A second CK-MB and myoglobin test should have been performed at 3 hours postadmission to confirm AMI
C. These results are consistent with skeletal muscle damage associated with a crush injury that elevated the CK-MB
D. Further testing 6–12 hours postadmission is required to establish a diagnosis of AMI

A

A. This patient has had an AMI and further testing is unnecessary

35
Q

SITUATION: An EDTA sample for TnI assay gives a result of 0.04 ng/mL (reference range 0–0.03 ng/mL). The test is repeated 3 hours later on a new specimen and the result is
0.06 ng/mL.
A third sample collected 6 hours later gives a result of 0.07 ng/mL. The EKG showed no evidence of ST segment elevation (STEMI). What is the most likely explanation? A. A false-positive result occurred due to matrix
interference
B. Heparin should have been used instead of EDTA, which causes false positives
C. The patient has suffered cardiac injury
D. The patient has had an ischemic episode without cardiac injury

A

C. The patient has suffered cardiac injury

36
Q

Which of the following laboratory tests is a marker for ischemic heart disease?
A. CK-MB isoforms
B. Myosin light chain 1
C. Albumin cobalt binding
D. Free fatty acid binding protein

A

C. Albumin cobalt binding

37
Q

Which test becomes abnormal in the earliest stage of the acute coronary syndrome?
A. Myosin light chain 1
B. CK-MB isoforms
C. Myoglobin
D. High-sensitivity C-reactive protein

A

D. High-sensitivity C-reactive protein

38
Q

Which statement best describes the clinical utility of B-type natriuretic peptide (BNP)?
A. Abnormal levels may be caused by obstructive
lung disease
B. A positive test indicates prior myocardial
damage caused by AMI that occurred within
the last 3 months
C. A normal test result (<100 pg/mL) helps rule
out congestive heart failure in persons with
symptoms associated with coronary insufficiency
D. A level above 100 pg/mL is not significant if evidence of congestive heart failure is absent

A

C. A normal test result (<100 pg/mL) helps rule
out congestive heart failure in persons with
symptoms associated with coronary insufficiency

39
Q

Which statement best describes the clinical utility of plasma homocysteine?
A. Levels are directly related to the quantity of LDL
cholesterol in plasma
B. High plasma levels are associated with
atherosclerosis and increased risk of thrombosis
C. Persons who have an elevated plasma
homocysteine will also have an increased
plasma Lp(a)
D. Plasma levels are increased only when there is an
inborn error of amino acid metabolism

A

B. High plasma levels are associated with
atherosclerosis and increased risk of thrombosis

40
Q

Which of the following cardiac markers derived from neutrophils predicts an increased risk for myocardial infarction?
A. Phospholipase A2 (PLA2)
B. Glycogen phosphorylase BB (GPBB)
C. Soluble CD40 ligand (sCD40l)
D. Myeloperoxidase (MPO)

A

D. Myeloperoxidase (MPO)

41
Q

Which of the following statements about the aminotransferases (AST and ALT) is true?
A. Isoenzymes of AST and ALT are not found in
humans
B. Both transfer an amino group to α–ketoglutarate
C. Both require NADP+ as a coenzyme
D. Both utilize four carbon amino acids as substrates

A

B. Both transfer an amino group to α–ketoglutarate

42
Q

Select the products formed from the forward reaction of AST.
A. Alanine and α–ketoglutarate
B. Oxaloacetate and glutamate
C. Aspartate and glutamine
D. Glutamate and NADH

A

B. Oxaloacetate and glutamate

43
Q

Select the products formed from the forward reaction of ALT.
A. Aspartate and alanine
B. Alanine and α–ketoglutarate
C. Pyruvate and glutamate
D. Glutamine and NAD+

A

C. Pyruvate and glutamate

44
Q

Which of the statements below regarding the methods of Henry for AST and ALT is correct?
A. Hemolysis will cause positive interference in both AST and ALT assays
B. Loss of activity occurs if samples are frozen at –20°C
C. The absorbance at the start of the reaction should
not exceed 1.0 A
D. Reaction rates are unaffected by addition of
P-5 ́-P to the substrate

A

A. Hemolysis will cause positive interference in both AST and ALT assays

45
Q

Select the coupling enzyme used in the kinetic AST reaction of Henry.
A. LD
B. Malate dehydrogenase
C. Glutamate dehydrogenase
D. G-6-PD

A

B. Malate dehydrogenase

46
Q

What is the purpose of LD in the kinetic method of Henry for AST?
A. Forms NADH, enabling the reaction to be
monitored at 340 nm
B. Rapidly exhausts endogenous pyruvate in the
lag phase
C. Reduces oxaloacetate, preventing product
inhibition
D. Generates lactate, which activates AST

A

B. Rapidly exhausts endogenous pyruvate in the
lag phase

47
Q

Which of the following statements regarding the naming of transaminases is true?
A. Serum glutamic oxaloacetic transaminase
(SGOT) is the older abbreviation for ALT
B. Serum glutamic pyruvic transaminase (SGPT) is
the older abbreviation for AST
C. SGPT is the older abbreviation for ALT
D. SGOT is the newer abbreviation for AST

A

C. SGPT is the older abbreviation for ALT

48
Q

Which statement accurately describes serum transaminase levels in AMI?
A. ALT is increased 5- to 10-fold after an AMI
B. AST peaks 24–48 hours after an AMI and
returns to normal within 4–6 days
C. AST levels are usually 20–50 times the upper
limit of normal after an AMI
D. Isoenzymes of AST are of greater diagnostic
utility than the total enzyme level

A

B. AST peaks 24–48 hours after an AMI and
returns to normal within 4–6 days

49
Q

Which condition gives rise to the highest serum level of transaminases?
A. Acute hepatitis
B. Alcoholic cirrhosis
C. Obstructive biliary disease
D. Diffuse intrahepatic cholestasis

A

A. Acute hepatitis

50
Q

In which liver disease is the DeRitis ratio (ALT:AST) usually greater than 1.0?
A. Acute hepatitis
B. Chronic hepatitis
C. Hepatic cirrhosis
D. Hepatic carcinoma

A

A. Acute hepatitis

51
Q

Which of the following liver diseases produces the highest levels of transaminases?
A. Hepatic cirrhosis
B. Obstructive jaundice
C. Hepatic cancer
D. Alcoholic hepatitis

A

C. Hepatic cancer

52
Q

Which of the following statements regarding transaminases is true?
A. ALT is often increased in muscular disease,
pancreatitis, and lymphoma
B. ALT is increased in infectious mononucleosis,
but AST is usually normal
C. ALT is far more specific for liver diseases than
is AST
D. Substrate depletion seldom occurs in assays of
serum from hepatitis cases

A

C. ALT is far more specific for liver diseases than
is AST

53
Q

Select the most sensitive marker for alcoholic liver disease.
A. GLD
B. ALT
C. AST
D. γ-Glutamyltransferase (GGT)

A

D. γ-Glutamyltransferase (GGT)

54
Q

Which enzyme is least useful in differentiating necrotic from obstructive jaundice?
A. GGT
B. ALT
C. 5’ Nucleotidase
D. LD

A

D. LD

CC HARR (3 decks)

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