Enzymes and Cardiac Markers

Question 1

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

Answer 1

C

Question 2

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

Answer 2

A

Question 3

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

Answer 3

C

Question 4

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

Answer 4

D

Question 5

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] =

Answer 5

A

Question 6

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

Answer 6

A

Question 7

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

Answer 7

A

Question 8

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

Answer 8

D

Question 9

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

Answer 9

D

Question 10

Which of the following enzymes is activated by
calcium ions?
A. CK
B. Amylase
C. ALP
D. LD

Answer 10

B

Question 11

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

Answer 11

B

Question 12

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

Answer 12

B

Question 13

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

Answer 13

B

Question 14

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

Answer 14

A

Question 15

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

Answer 15

C

Question 16

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

Answer 16

D

Question 17

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

Answer 17

A

Question 18

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

Answer 18

A

Question 19

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

Answer 19

A

Question 20

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

Answer 20

A

Question 21

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

Answer 21

C

Question 22

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

Answer 22

D

Question 23

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

Answer 23

C

Question 24

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

Answer 24

C

Question 25

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

Answer 25

C

Question 26

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%

Answer 26

B

Question 27

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

Answer 27

A

Question 28

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

Answer 28

B

Question 29

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

Answer 29

C

Question 30

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

Answer 30

C

Question 31

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

Answer 31

C

Question 32

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

Answer 32

B

Question 33

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

Answer 33

B

Question 34

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

Answer 34

D

Question 35

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

Answer 35

D

Question 36

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

Answer 36

C

Question 37

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

Answer 37

D

Question 38

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

Answer 38

C

Question 39

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

Answer 39

B

Question 40

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)

Answer 40

D

Question 41

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

Answer 41

B

Question 42

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

Answer 42

B

Question 43

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+

Answer 43

C

Question 44

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

Answer 44

A

Question 45

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

Answer 45

B

Question 46

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

Answer 46

B

Question 47

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

Answer 47

B

Question 48

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

Answer 48

C

Question 49

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

Answer 49

B

Question 50

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

Answer 50

A

Question 51

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

Answer 51

A

Question 52

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

Answer 52

C

Question 53

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

Answer 53

C

Question 54

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

Answer 54

D

Question 55

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

Answer 55

D

Question 56

Which of the following statements about the phosphatases is true? A. They hydrolyze adenosine triphosphate and related compounds B. They are divided into two classes based upon pH needed for activity C. They exhibit a high specificity for substrate D. They are activated by Pi

Answer 56

B

Question 57

Which of the following statements regarding ALP is true? A. In normal adults, the primary tissue source is fast-twitch skeletal muscle B. Geriatric patients have a lower serum ALP than other adults C. Serum ALP levels are lower in children than in adults D. Pregnant women have a higher level of serum ALP than other adults

Answer 57

D

Question 58

Which isoenzyme of ALP is most heat stable? A. Bone B. Liver C. Intestinal D. Placental

Answer 58

D

Question 59

Which isoenzyme of ALP migrates farthest toward the anode when electrophoresed at pH 8.6? A. Placental B. Bone C. Liver D. Intestinal

Answer 59

C

Question 60

Which statement regarding bone-specific ALP is true? A. The bone isoenzyme can be measured immunochemically B. Bone ALP is increased in bone resorption C. Bone ALP is used for the diagnosis of osteoporosis D. There are two distinct bone isoenzymes

Answer 60

A

Question 61

Which of the following statements regarding ALP is true? A. All isoenzymes of ALP are antigenically distinct and can be identified by specific antibodies B. Highest serum levels are seen in intrahepatic obstruction C. Elevated serum ALP seen with elevated GGT suggests a hepatic source D. When jaundice is present, an elevated ALP suggests acute hepatitis

Answer 61

C

Question 62

In which condition would an elevated serum alkaline phosphatase be likely to occur? A. Small cell lung carcinoma B. Hemolytic anemia C. Prostate cancer D. Acute myocardial infarction

Answer 62

A

Question 63

Which condition is least likely to be associated with increased serum ALP? A. Osteomalacia B. Biliary obstruction C. Hyperparathyroidism and hyperthyroidism D. Osteoporosis

Answer 63

D

Question 64

Which substrate is used in the Bowers–McComb method for ALP? A. p-Nitrophenyl phosphate B. β-Glycerophosphate C. Phenylphosphate D. α-Naphthylphosphate

Answer 64

A

Question 65

Which of the following buffers is used in the IFCC recommended method for ALP? A. Glycine B. Phosphate C. 2-Amino-2-methyl-1-propanol D. Citrate

Answer 65

C

Question 66

A serum ALP level greater than twice the elevation of GGT suggests: A. Misidentification of the specimen B. Focal intrahepatic obstruction C. Acute alcoholic hepatitis D. Bone disease or malignancy

Answer 66

D

Question 67

In which condition is the measurement of acid phosphatase clinically useful? A. Measuring the prostatic isoenzyme to screen for prostate cancer B. Measuring the enzyme in a vaginal swab extract C. The diagnosis of hemolytic anemia D. As a marker for bone regeneration

Answer 67

B

Question 68

Which definition best describes the catalytic activity of amylase? A. Hydrolyzes second α 1–4 glycosidic linkages of starch, glycogen, and other polyglucans B. Hydrolyzes all polyglucans completely to produce glucose C. Oxidatively degrades polysaccharides containing glucose D. Splits polysaccharides and disaccharides by addition of water Chemistry/Apply knowl

Answer 68

A

Question 69

Which of the following amylase substrates is recommended by the IFCC? A. Starch B. Maltodextrose C. Maltotetrose D. Blocked maltohepatoside

Answer 69

D

Question 70

How soon following acute abdominal pain due to pancreatitis is the serum amylase expected to rise? A. 1–2 hours B. 2–12 hours C. 3–4 days D. 5–6 days

Answer 70

B

Question 71

Which of the following statements regarding the diagnosis of pancreatitis is correct? A. Amylase and lipase are as predictive in chronic as in acute pancreatitis B. Diagnostic sensitivity is increased by assaying both amylase and lipase C. Measuring the urinary amylase:creatinine ratio is useful only when patients have renal failure D. Serum lipase peaks several hours before amylase after an episode of acute pancreatitis

Answer 71

B

Question 72

Which of the following conditions is associated with a high level of S-type amylase? A. Mumps B. Intestinal obstruction C. Alcoholic liver disease D. Peptic ulcers

Answer 72

A

Question 73

Which of the following statements regarding amylase methods is true? A. Requires sulfhydryl compounds for full activity B. Activity will vary depending on the method used C. Amyloclastic methods measure the production of glucose D. Overrange samples are diluted in deionized water

Answer 73

B

Question 74

Which of the following statements regarding amylase methods is true? A. Dilution of serum may result in lower than expected activity B. Methods generating NADH are preferred because they have higher sensitivity C. Synthetic substrates can be conjugated to p-nitrophenol (PNP) for a kinetic assay D. The reference range is consistent from method to method

Answer 74

C

Question 75

The reference method for lipase uses olive oil as the substrate because: A. Other esterases can hydrolyze triglyceride and synthetic diglycerides B. The reaction product can be coupled to NADH generating reactions C. Synthetic substrates are less soluble than olive oil in aqueous reagents D. Triglyceride substrates cause product inhibition

Answer 75

A

Question 76

Which statement about the clinical utility of plasma or serum lipase is true? A. Lipase is not increased in mumps, malignancy, or ectopic pregnancy B. Lipase is not increased as dramatically as amylase in acute pancreatitis C. Increased plasma or serum lipase is specific for pancreatitis D. Lipase levels are elevated in both acute and chronic pancreatitis

Answer 76

A

Question 77

The reference method for serum lipase is based upon: A. Assay of triglycerides following incubation of serum with olive oil B. Rate turbidimetry C. Titration of fatty acids with dilute NaOH following controlled incubation of serum with olive oil D. Immunochemical assay

Answer 77

C

Question 78

The most commonly employed method of assay for plasma or serum lipase is based on: A. Hydrolysis of olive oil B. Rate turbidimetry C. Immunoassay D. Peroxidase coupling

Answer 78

D

Question 79

Which of the following enzymes is usually depressed in liver disease? A. Elastase-1 B. GLD C. Pseudocholinesterase D. Aldolase

Answer 79

C

Question 80

Which of the following enzymes is usually depressed in liver disease? A. Elastase-1 B. GLD C. Pseudocholinesterase D. Aldolase

Answer 80

C

Question 81

Which enzyme is most likely to be elevated in the plasma of a person suffering from a muscle wasting disorder? A. 5´-Nucleotidase B. Pseudocholinesterase C. Aldolase D. Glutamate dehydrogenase

Answer 81

C

Question 82

Which enzyme is measured in whole blood? A. Chymotrypsin B. Glucose-6-phosphate dehydrogenase C. Glycogen phosphorylase D. Lipase

Answer 82

B

Question 82

Which enzyme is most likely to be elevated in the plasma of a person suffering from a muscle wasting disorder? A. 5´-Nucleotidase B. Pseudocholinesterase C. Aldolase D. Glutamate dehydrogenase

Answer 82

C