Chemistry 6.6 Enzymes and Cardiac Markers Flashcards
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 deciliter
C. Converts 1 µmol of substrate to product per minute
Which of the following measurement modes does not allow for continuous monitoring of enzyme activity?
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. Initial absorbance is measured followed by a second reading after 5 minutes
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
C. The enzyme increases the rate of the reaction
Which statement about enzymes is true?
A. An enzyme alters the Gibbs 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
D. A competitive inhibitor will alter the apparent Km of the reaction
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. Greater than 99 × Km
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. Apoenzyme + prosthetic group = holoenzyme
Which of the following statements about enzymatic reactions is true?
A. NADH has absorbance maxima 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. NADH has absorbance maxima at 340 and 366 nm
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
D. Increased production and secretion by cells
Which of the following enzymes is considered most tissue specific?
A. CK
B. Amylase
C. ALP
D. ADH
D. ADH
Which of the following enzymes is activated by calcium ions?
A. CK
B. Amylase
C. ALP
D. LD
B. Amylase
Which of the following enzymes is a transferase?
A. ALP
B. CK
C. Amylase
D. LD
B. CK
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
B. The pyruvate-to-lactate reaction proceeds at about twice the rate as the forward reaction
Which condition produces the highest elevation of serum lactate dehydrogenase (LD)?
A. Pernicious anemia
B. Myocardial infarction
C. Acute hepatitis
D. Muscular dystrophy
A. Pernicious anemia
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
C. Acute appendicitis
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
D. 1:2 or less
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. Toxic hepatitis
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. Slight hemolysis during sample collection
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. Hexokinase and G-6-PD
In the Oliver-Rosalki method for CK, AMP is added to the substrate 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. Inhibit adenylate kinase
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
C. N-acetylcysteine
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
C. An endogenous competitive inhibitor is present in the serum
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
D. Reject the sample because the citrate will interfere
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 muscular dystrophy
D. The enzyme is highly specific for heart injury
C. Highest levels are seen in Duchenne muscular dystrophy
A patient’s CK-MB isoenzyme concentration 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%
B. 3.2%
CKI = (CK-BM in ug/L)/(Total CK in IU/L) * 100
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 troponin I (TnI)
D. A more modest increase in total CK than CK-MB
A. An increase in CK-MB that is persistent
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 to 4 hours after admission help exclude a diagnosis of AMI
C. Myoglobin peaks after the cardiac troponins but is more sensitive
D. The persistence of myoglobin greater than 110 µg/L for 3 days after chest pain favors a diagnosis of AMI
B. Levels below 100 µg/L on admission and 2 to 4 hours after admission help exclude a diagnosis of AMI
Which statement best describes cardiac troponin I and T?
A. An enzyme embedded in the endocardium released after MI
B. Two polypeptides that regulate the sliding of contractile proteins in cardiac muscle
C. A peptide that is released in response to ventricular stretching
D. A prohormone released from the pericardium in response to injury
B. Two polypeptides that regulate the sliding of contractile proteins in cardiac muscle
What requirements must be met for a troponin assay to be considered a high-sensitivity test?
A. Must have a detection limit of 30 ng/L
B. Must be able to give a value for 100% of the healthy population who have a concentration above the limit of detection
C. Must have a coefficient of variation (CV) of less than 10% at the 99th percentile of the healthy population
D. Must have a clinical specificity of 99% or greater
C. Must have a coefficient of variation (CV) of less than 10% at the 99th percentile of the healthy population
What is the typical time course for high-sensitivity (guideline compliant) cardiac troponin I (cTnI) or cardiac troponin T (cTnT) following an AMI?
A. Abnormal within 1 hour; peak within 24 hours; return to normal in 7 to 10 days
B. Abnormal within 4 hours; peak within 18 hours; return to normal in 48 hours
C. Abnormal within 4 hours; peak within 24 hours; return to normal in 3 days
D. Abnormal within 6 hours; peak within 36 hours; return to normal in 5 days
A. Abnormal within 1 hour; peak within 24 hours; return to normal in 7 to 10 days
What protocol is needed to rule out an MI with a high-sensitivity troponin assay?
A. A single sample at arrival
B. Serial samples for up to 3 hours after arrival
C. Serial samples for up to 6 hours after arrival
D. A minimum of four samples over 4 hours
B. Serial samples for up to 3 hours after arrival
Which statement best describes the clinical significance of a single cTnI or cTnT result that is slightly above the limit of detection?
A. A positive test in the absence of laboratory error is diagnostic of MI
B. A positive test in the absence of laboratory error or in vitro false positive result indicates cardiac injury
C. Serial increases indicate necrosis caused by plaque rupture or thrombosis
D. Serial increases indicate S-T segment elevated myocardial infarction (STEMI)
B. A positive test in the absence of laboratory error or in vitro false positive result indicates cardiac injury
Which of the following cardiac markers is most often increased in persons who exhibit unstable angina?
A. Troponin C
B. cTnT
C. CK-MB
D. Myoglobin
B. cTnT