Clinical Chemistry

Front 1

Which instrumentation principle or use is INCORRECTLY described?
a. Nephelometry is used to measure large particle concentrations.
b. The principle of freezing point osmometry is related to the heat of fusion.
c. Crystal scintillation is primarily used to detect beta radiation using sodium iodide crystals that contain thallium.
d. Nuclear magnetic resonance spectroscopy is a technique for determining inorganic compound structures in a process that, like mass
spectroscopy, destroys the compound.
e. Capillary electrophoresis is a separation technique using a high voltage and electro-osmotic flow to move excess positive ions toward
the cathode.

Back 1

d.
NMR determines structures of organic compounds and, unlike MS, is not destructive. The other statements correctly describe each
corresponding instrumentation principle.

Front 2

Which of the following statements about electrochemistry is FALSE?
a. An ideal reference electrode should exhibit a potential that is constant with time.
b. The calomel electrode makes use of sodium bicarbonate buffer and a gas-permeable membrane.
c. The pH electrode is a glass electrode that measures hydrogen ion activity.
d. The ion-selective electrode is an electrochemical transducer capable of responding to one specific ion.
e. The polypropylene membrane is often associated with the PO2 electrode and is effective in preventing blood constituents other than
oxygen from passing through.

Back 2

b.
The PCO2 electrode uses sodium bicarbonate buffer and a gas-permeable membrane. The calomel electrode is made of mercury
that is in contact with a mercury (I) chloride-saturated solution. This solution is referred to as “calomel” and contains a known
concentration of potassium chloride. The other choices correctly describe each of the corresponding electrodes.

Front 3

The phenomenon of electroendosmosis:
a. Describes the faster migration of substances when increased osmotic activity buffers are used.
b. Is the cause for the more anodal migration of immunoglobulins in serum protein electrophoresis.
c. Is caused by hydronium ions in solvents, attracted to the negative charge on the electrophoretic medium, moving toward the negatively
charged pole in the system.
d. Occurs with all types of electrophoretic media.
e. Should be prevented by use of low osmotic activity solutes and nonaqueous buffer solutions to avoid artifacts of separation.

Back 3

c.
Electroendosmosis describes the paradoxical migration of charged molecules (such as immunoglobulins) in a direction contrary to
what would be expected. When support media with a negative surface charge (such as cellulose acetate or agarose) are used,
hydronium ions (as H3O+) are attracted to the surface and migrate toward the cathode (negatively charged) pole. The weak
negative charge on proteins such as immunoglobulins causes them to be carried along with the solvent toward the cathode,
instead of the expected migration toward the anode. Electroendosmosis does not occur with uncharged support media such as
polyacrylamide gel or starch gel. It improves separation of proteins, and thus is helpful in analysis of serum proteins.

Front 4

When proteins are denatured (such as by sodium dodecyl sulfate), polyacrylamide gel primarily separates them on the basis of:
a. Charge
b. Charge density
c. Degree of folding
d. Molecular length
e. Molecular weight

Back 4

e.
SDS-PAGE separates the denatured proteins primarily on the basis of molecular weight. Charge density is the most important
factor in electrophoresis with nondenatured proteins. Degree of folding is irrelevant when proteins are denatured.

Front 5

In agarose gel electrophoresis, all of the following are important in affecting the separation of substances EXCEPT:
a. Ionic strength of the buffer
b. pH of the buffer
c. Temperature of the system
d. Time of electrophoresis
e. Voltage applied to the gel

Back 5

c.
Temperature does not directly affect separation of compounds in electrophoresis; however, cooling is often used to prevent protein
denaturation, which may affect migration of proteins. All of the other variables can be adjusted to improve separation of
compounds in electrophoresis.

Front 6

Which of the following is NOT a feature or benefit of point-of-care testing (POCT)?
a. Improved turnaround time for laboratory results
b. Less traumatic and less blood (for fingerstick systems)
c. Decreased manpower requirements in the central laboratory
d. Ease of use for serum or plasma
e. Built-in quality control systems

Back 6

d.
Whole blood would have to be centrifuged to assay serum or plasma. Centrifugation is not a feature consistent with the use of
point-of-care testing devices. Sampling volumes are often smaller and are less traumatic for the patient, and built-in quality control
checks lend to the ease of use.

Front 7

Which of the following is NOT a synonym or alternate name meaning point-of-care testing?
a. Ancillary testing
b. Decentralized testing
c. Distributed testing
d. Platform testing

Back 7

d.
Testing done on an analytical platform or bench-top analyzer would likely be a test performed in the main laboratory and would
therefore not be a point-of-care test.

Front 8

Which statement LEAST describes point-of-care testing (POCT)?
a. The driving forces behind the use of POCT differ distinctly depending on the setting.
b. A significant potential benefit of POCT in the hospital setting is more rapid and (ideally) more effective assessment and management of
critically ill patients.
c. POCT analyzers have less disposables and lower reagent costs than traditional laboratory systems and are therefore less expensive to
operate.
d. The use of POCT systems is subject to regulations associated with the clinical laboratory testing.
e. Ultimate responsibility and control of POCT reside within an accreditation agency and require at least one laboratorian to be responsible for each POC program.

Back 8

c.
POCT analyzers generate more disposables, and reagent costs are usually more expensive than traditional laboratory systems.
One of the main drawbacks of POCT systems is the expensive price.

Front 9

Which statement regarding clinical enzymology is FALSE?
a. Enzyme reactions generally proceed at zero order kinetics immediately following the lag phase.
b. When plotting a Lineweaver-Burk plot of a Michaelis-Menten enzyme in the presence of a competitive inhibitor, the value for 1/Vmax is
constant for different concentrations of inhibitor.
c. In uncompetitive inhibition, the inhibitor binds only to the free enzyme and not to the enzyme-substrate complex.
d. ATP can serve as the rate-limiting step for coupled enzyme reactions.
e. When plotting a Lineweaver-Burk plot of a Michaelis-Menten enzyme in the presence of a noncompetitive inhibitor, lines of different slope
correspond to different values of inhibitor concentration.

Back 9

c.
In classic noncompetitive inhibition, the inhibitor binds only to the free enzyme and not to the enzyme-substrate complex. In
uncompetitive inhibition, the inhibitor binds only to the enzyme-substrate complex and not to the free enzyme. Therefore, no
enzymeinhibitor complex will form, and binding of the substrate will lead to a conformational change that will create an inhibitor
binding site.

Front 10

Which of the following statements regarding a specific enzyme is FALSE?
a. Acid phosphatase in serum is generally stable at all temperatures as long as the pH is above 7.
b. Lactate dehydrogenase is an example of an enzyme whose presence in plasma may indicate cellular damage.
c. The reference range for alkaline phosphatase is generally higher for children than it is for adults.
d. Alcohol dehydrogenase levels in the gastric mucosa of males are generally higher than in females.
e. Patients who have been at complete bed rest for several days generally have significantly lower values for creatine kinase.

Back 10

a.
Acid phosphatase is unstable at all temperatures unless the pH of the serum is reduced to between 5 and 6.

Front 11

Which of the following enzymes has the LOWEST red cell:serum activity ratio?
a. Aspartate transaminase
b. Alanine aminotransferase
c. Lactate dehydrogenase
d. Creatine kinase

Back 11

d.
Red cells do not contain creatine kinase. The highest ratio would be seen with lactate dehydrogenase (around 500:1). The ratio of
AST is about 15:1, while that of ALT is about 7:1.

Front 12

Which of the following cholinesterase statements is FALSE?
a. Pseudocholinesterase can be used to monitor exposure to cholinesterase inhibitors.
b. Organophosphate insecticides are irreversible inhibitors of both pseudocholinesterase and acetylcholinesterase.
c. Pseudocholinesterase measurement can provide a good assessment of liver injury.
d. Acetylcholinesterase can be identified in amniotic fluid from pregnancies with neural tube defects.
e. Pseudocholinesterase testing can be used to recognize genetic variants in individuals demonstrating apnea during succinyl choline
administration

Back 12

c.
In contrast to other hepatocyte enzymes, pseudocholinesterase production by the liver reflects hepatic synthetic function rather
than hepatocyte injury.

Front 13

A 34-year-old who is taking prescribed oxycodone for pain has a positive drug screen for opiate and methadone. The confirmatory test is performed by a reference laboratory via gas chromatography mass spectrometry. This confirmatory
test for opiates is positive for oxycodone, hydromorphone, and hydrocodone only (negative for methadone). The clinician taking care of
the patient is concerned about possible interferences with the positive results and calls the laboratory to ask if the patient is taking
other narcotics besides the prescribed OxyContin. Which of the following would be an INCORRECT statement about this case?

Back 13

c.
Very little interferes with screening tests for methadone. It is possible that methadone does not show up on confirmation because
of the specific method used in the laboratory. Also, many reference laboratories such as the Mayo Clinic identify methadone
separately, and it is not part of their screen to confirm opiates. Hydrocodone and hydromorphone are not metabolites nor do they
interfere with methadone or oxycodone detection. Because both were found on gas chromatography mass spectrometry
confirmation, a third drug is indicated. Methadone is likely the cause of the positive test result.

Front 14

An 18-year-old man was admitted with multiple broken bones, a punctured lung, and a ruptured spleen after an automobile accident.
He was driving the car. A passenger in his car was also admitted to the emergency room; however, he died from multiple injuries
shortly after admission. The police are waiting for the driver to recover because their intent is to arrest him for manslaughter for being
under the influence of alcohol and drugs at the time of the accident. A serum alcohol obtained at the time of admission was 11 mg/dL
(110 mg/L), and a urine drug screen was positive for cannabinoids. Of the following, the best statement that can be made about the
driver is that he is:
a. Under the influence of alcohol and marijuana
b. Under the influence of alcohol but not marijuana
c. Under the influence of marijuana but not alcohol
d. Under the influence of neither alcohol nor marijuana
e. None of the above

Back 14

e.
The legal limit for alcohol is 80 mg/dL (equivalent to “blowing” a 0.08 on a breathalyzer). Additionally, only whole blood (not serum)
analyzed by head space gas chromatography from a chain-of-custody sample can be used to define a legal/forensic alcohol level.
The driver's measured level of 11 mg/dL (equivalent to blowing a 0.011) does not indicate impairment. Impairment is reported to
begin at 40 mg/dL. Blood alcohol levels between 0.02 and 0.03 are associated with slight euphoria and loss of shyness but are not
usually associated with loss of coordination. Depressant effects are not apparent at these levels. The presence of marijuana
indicates past exposure and does not prove that an individual is under the influence of the drug. Urine immunoassays are
screening tests, not confirmatory tests.

Front 15

Which of the choices listed is the best method for collecting and storing a sample for forensic analysis to determine the possibility
of ethanol and cocaine use? Assume proper chain of custody procedures is followed.
a. Whole blood collected in a red-top tube (no preservative) and refrigerated (4°C) for 2 months
b. Adipose tissue immediately fixed in formalin
c. Whole blood collected in a grey-top tube (NaF) at the time of death and frozen for 2 months
d. Whole blood collected in a red-top tube and stored at room temperature for 3 days
e. Serum or plasma that is immediately separated and frozen at the time of autopsy

Back 15

c.
NaF is preferred for collecting samples from individuals who are suspected of cocaine use. Cocaine is metabolized by hydrolysis
of ester linkages. In blood, cocaine is hydrolyzed to ecgonine methyl ester via cholinesterase. This reaction is dependent on the
concentration of cocaine and may be inhibited by freezing or addition of fluoride or cholinesterase inhibitors. At 4°C 1 mg/L of
cocaine will loose 100% of the parent drug after 21 days.

Front 16

Creatinine Clearance (ml / min)

Back 16

Creatinine Clearance (ml / min) = (Urine Creatinine / Serum Creatinine) x Urine Volume (ml) / [ time (hr) x 60 ]