Clinical Chemistry- Clinical Chemistry Problem Solving Flashcards
- Which of the following procedures can be used to
detect proportional error in a new method for
glucose?
A. Compare the standard deviation of 40 patient
samples to the hexokinase method
B. Measure a mixture made from equal parts of
normal and high-QC sera
C. Add 5.0 mg of glucose to 1.0 mL of a serum of
known concentration and measure
D. Compare the mean of 40 normal samples to the
hexokinase method
C. Add 5.0 mg of glucose to 1.0 mL of a serum of
known concentration and measure
- Which of two instruments can be assumed to have
the narrower bandpass? Assume that wavelength is
accurately calibrated.
A. The instrument giving the highest absorbance for
a solution of 0.1 mmol/L NADH at 340 nm
B. The instrument giving the lowest %T for a
solution of nickel sulfate at 700 nm
C. The instrument giving the highest %T reading
for 1.0% v/v HCl at 350 nm
D. The instrument giving the most linear plot of
absorbance versus concentration
A. The instrument giving the highest absorbance for
a solution of 0.1 mmol/L NADH at 340 nm
- A lipemic sample gives a sodium of 130 mmol/L
on an analyzer that uses a 1:50 dilution of serum
or plasma before introducing it to the ion selective
electrodes. The same sample gives a sodium of
142 mmol/L using a direct (undiluted) ion
selective electrode. Assuming acceptable quality
control, which of the following is the most
appropriate course of action?
A. Report a sodium result of 136 mmol/L
B. Ultracentrifuge the sample and repeat by ISE
C. Dilute the sample 1:4 and repeat by ISE
D. Report the undiluted ion selective electrode
result
D. Report the undiluted ion selective electrode
result
- SITUATION: A 22S QC error occurs for serum
calcium by atomic absorption. Fresh standards
prepared in 5.0% w/v albumin are found to be
linear, but repeating the controls with fresh
material does not improve the QC results. Select
the most likely cause of this problem.
A. Matrix effect caused by a viscosity difference
between the standards and QC sera
B. Chemical interference caused incomplete
atomization
C. Incomplete deconjugation of protein-bound
calcium
D. Ionization interference caused by excessive heat
B. Chemical interference caused incomplete
atomization
- SITUATION: A serum osmolality measured in
the emergency department is 326 mOsm/kg.
Two hours later, chemistry results are:
Na = 135 mmol/L
BUN = 18 mg/dL
glucose = 72 mg/dL measured osmolality = 318
mOsm/kg
What do these results suggest?
A. Laboratory error in electrolyte or glucose
measurement
B. Drug or alcohol intoxication
C. Specimen misidentification
D. Successful rehydration of the patient
B. Drug or alcohol intoxication
- When calibrating a pH meter, unstable readings
occur for both pH 7.00 and 4.00 calibrators,
although both can be set to within 0.1 pH unit.
Select the most appropriate course of action.
A. Measure the pH of the sample and report to the
nearest 0.1 pH
B. Replace both calibrators with unopened buffers
and recalibrate
C. Examine the reference electrode junction for salt
crystals
D. Move the electrodes to another pH meter and
calibrate
C. Examine the reference electrode junction for salt
crystals
- A method calls for extracting an acidic drug from
urine with an anion exchange column. The pKa
of the drug is 6.5. Extraction is enhanced by
adjusting the sample pH to:
A. 8.5
B. 6.5
C. 5.5
D. 4.5
A. 8.5
- SITUATION: A patient who has a positive
urinalysis for glucose and ketones has a glycated
Hgb of 4.0%. A fasting glucose performed the
previous day was 180 mg/dL. Assuming acceptable
QC, you would:
A. Report the glycosylated Hgb
B. Request a new specimen and repeat the
glycosylated Hgb
C. Perform a Hgb electrophoresis on the sample
D. Perform a glucose measurement on the sample
B. Request a new specimen and repeat the
glycosylated Hgb
- Quality control results for uric acid are as follows:
Results should be reported from:
A. Run 1 only
B. Runs 1 and 2
C. Runs 1, 2, and 3
D. Runs 1, 2, 3, and 4
C. Runs 1, 2, and 3
- SITUATION: A peak blood level for orally
administered theophylline (therapeutic
range 8–20 mg/L) measured at 8 a.m. is
5.0 mg/L. The preceding trough level was
4.6 mg/L. What is the most likely explanation
of these results?
A. Laboratory error made on peak measurement
B. Specimen for peak level was collected from
wrong patient
C. Blood for peak level was drawn too soon
D. Elimination rate has reached maximum
C. Blood for peak level was drawn too soon
- SITUATION: A patient breathing room air has the
following arterial blood gas and electrolyte results:
pH = 7.54
PCO2 = 18.5 mm Hg
PO2 = 145 mm Hg
HCO3 = 18 mmol/L
Na = 135 mmol/L
K = 4.6 mmol/L
Cl = 98 mmol/L
TCO2 = 20 mmol/L
The best explanation for these results is:
A. Blood for electrolytes was drawn above an IV
B. Serum sample was hemolyzed
C. Venous blood was sampled for arterial blood
gases
D. Blood gas sample was exposed to air
D. Blood gas sample was exposed to air
- SITUATION: The following lab results are
reported. Which result is most likely to be
erroneous?
Arterial blood gases:
pH = 7.42
pO2 = 90 mm Hg
pCO2 = 38.0 mm Hg bicarbonate = 24 mmol/L.
Plasma electrolytes:
Na = 135 mmol/L
Cl = 98 mmol/L
K = 4.6 mmol/L
TCO2 = 33 mmol/L
A. pH
B. Na
C. K
D. TCO2
D. TCO2
- SITUATION: Laboratory results on a patient from
the emergency department are:
glucose =1,100 mg/dL
Na = 155 mmol/L
K = 1.2 mmol/L
Cl = 115 mmol/L
TCO2 = 3.0 mmol/L
What is the most likely explanation of these
results?
A. Sample drawn above an IV
B. Metabolic acidosis with increased anion gap
C. Diabetic ketoacidosis
D. Laboratory error measuring electrolytes caused
by hyperglycemia
A. Sample drawn above an IV
- SITUATION: A plasma sample from a person in a
coma as a result of an automobile accident gave the following results:
Total CK 480 IU/L CK-MB 8 μg/L
Myoglobin 800 μg/L Troponin I 0.02 μg/L
What is the best interpretation of these results?
A. The person had a heart attack that caused the
accident
B. The accident caused traumatic injury, but no
heart attack occurred
C. A heart attack occurred in addition to a stroke
D. It is not possible to tell whether a heart attack
occurred because of the extensive trauma
B. The accident caused traumatic injury, but no
heart attack occurred
- SITUATION: A patient has the following
electrolyte results:
Na = 130 mmol/L
K = 4.8 mmol/L
Cl = 105 mmol/L
TCO2 = 26 mmol/L
Assuming acceptable QC, select the best course
of action.
A. Report these results
B. Check the albumin, total protein, Ca, P, and
Mg results; if normal, repeat the sodium test
C. Request a new sample
D. Recalibrate and repeat the potassium test
B. Check the albumin, total protein, Ca, P, and
Mg results; if normal, repeat the sodium test
- A stat plasma lithium determined using an
ion-selective electrode is measured at
14.0 mmol/L. Select the most appropriate
course of action.
A. Immediately report this result
B. Check sample for hemolysis
C. Call for a new specimen
D. Rerun the lithium calibrators
C. Call for a new specimen
- A chromatogram for blood alcohol (GC) gives
broad trailing peaks and increased retention times
for ethanol and internal standard. This is most
likely caused by:
A. A contaminated injection syringe
B. Water contamination of the column packing
C. Carrier gas flow rate that is too fast
D. Oven temperature that is too high
B. Water contamination of the column packing
- SITUATION: An amylase result is 550 U/L.
A 1:4 dilution of the specimen in NaCl gives
180 U/L (before mathematical correction for
dilution). The dilution is repeated with the same
results. The technologist should:
A. Report the amylase as 550 U/L
B. Report the amylase as 720 U/L
C. Report the amylase as 900 U/L
D. Dilute the sample 1:10 in distilled water
and repeat
B. Report the amylase as 720 U/L
- SITUATION: A patient’s biochemistry results are:
ALT = 55 IU/L
AST = 165 IU/L
glucose = 87 mg/dL
LD = 340 IU/L
Na = 142 mmol/L
K = 6.8 mmol/L
Ca = 8.4 mg/dL
Pi = 7.2 mg/dL
Select the best course of action.
A. Report results along with an estimate of the
degree of hemolysis
B. Repeat LD but report all other results
C. Request a new sample
D. Dilute the serum 1:2 and repeat AST and LD
A. Report results along with an estimate of the
degree of hemolysis
- A blood sample is left on a phlebotomy tray for
4.5 hours before it is delivered to the laboratory.
Which group of tests could be performed?
A. Glucose, Na, K, Cl, TCO2
B. Uric acid, BUN, creatinine
C. Total and direct bilirubin
D. CK, ALT, ALP, AST
B. Uric acid, BUN, creatinine
- An HPLC assay for procainamide gives an
internal standard peak that is 15% greater in area
and height for sample 1 than sample 2. The
technologist should suspect that:
A. The column pressure increased while sample 2
was being analyzed
B. Less recovery from sample 2 occurred in the
extraction step
C. The pH of the mobile phase increased during
chromatography of sample 2
D. There was more procainamide in sample 1 than
sample 2
B. Less recovery from sample 2 occurred in the
extraction step
- After staining a silica gel plate to determine the
L/S ratio, the technologist notes that the lipid
standards both migrated 1 cm faster than usual.
The technologist should:
A. Repeat the separation on a new silica gel plate
B. Check the pH of the developing solvent
C. Prepare fresh developing solvent and repeat
the assay
D. Reduce solvent migration time for all
subsequent runs
C. Prepare fresh developing solvent and repeat
the assay
- A quantitative urine glucose was determined to
be 160 mg/dL by the Trinder glucose oxidase
method. The sample was refrigerated overnight.
The next day, the glucose is repeated and found to
be 240 mg/dL using a polarographic method.
What is the most likely cause of this discrepancy?
A. Poor precision when performing one of the
methods
B. Contamination resulting from overnight storage
C. High levels of reducing substances interfering
with the Trinder reaction
D. Positive interference in the polarographic
method caused by hematuria
C. High levels of reducing substances interfering
with the Trinder reaction
- SITUATION: Results of an iron profile are:
serum Fe = 40 μg/dL
TIBC = 400 μg/dL
ferritin = 40μg/L
transferrin = 300 mg/dL
(reference range 15–200)
These results indicate:
A. Error in calculation of TIBC
B. Serum iron falls before ferritin in iron deficiency
C. A defect in iron transport and not Fe deficiency
D. Excess release of ferritin caused by injury
D. Excess release of ferritin caused by injury
- SITUATION: Results of an iron profile are:
Serum Fe =40 μg/dL
TIBC =400 μg/dL
ferritin = 50 μg/L
All of the following tests are useful in establishing
a diagnosis of Fe deficiency except:
A. Protein electrophoresis
B. Erythrocyte zinc protoporphyrin
C. Serum transferrin
D. Hgb electrophoresis
D. Hgb electrophoresis
- Serum protein and immunofixation electrophoresis
are ordered on a patient. The former is performed,
but there is no evidence of a monoclonal protein.
Select the best course of action.
A. Perform quantitative Ig G, A, M
B. Perform the IFE on the serum
C. Report the result; request a urine sample for
protein electrophoresis
D. Perform IFE on the serum and request a urine
sample for IFE
C. Report the result; request a urine sample for
protein electrophoresis
- SITUATION: Hgb electrophoresis is performed
and all of the Hgbs have greater anodal mobility
than usual. A fast Hgb (Hgb H) is at the edge of
the gel and bands are blurred. The voltage is set
correctly, but the current reading on the ammeter
is too low. Select the course of action that would
correct this problem.
A. Reduce the voltage
B. Dilute the buffer and adjust the pH
C. Prepare fresh buffer and repeat the test
D. Reduce the running time
C. Prepare fresh buffer and repeat the test
- A technologist is asked to use the serum from a
clot tube left over from a chemistry profile run at
8 a.m. for a stat ionized calcium (Cai
) at 11 a.m.
The technologist should:
A. Perform the assay on the 8 a.m. sample
B. Perform the test only if the serum container was
tightly capped
C. Perform the assay on the 8 a.m. sample only if it
was refrigerated
D. Request a new sample
D. Request a new sample
- SITUATION: A patient’s biochemistry results are:
Na = 125 mmol/L
Cl = 106 mmol/L
K = 4.5 mmol/L
TCO2 = 19 mmol/L
chol = 240 mg/dL
triglyceride = 640 mg/dL glucose = 107 mg/dL
AST = 16 IU/L
ALT = 11 IU/L
amylase = 200 U/L
Select the most likely cause of these results.
A. The sample is hemolyzed
B. Serum was not separated from cells in
sufficient time
C. Lipemia is causing in vitro interference
D. The specimen is contaminated
C. Lipemia is causing in vitro interference
- A gastric fluid from a patient suspected of having
taken an overdose of amphetamine is sent to the
laboratory for analysis. The technologist should:
A. Perform an EMIT assay for amphetamine
B. Refuse the sample and request serum or urine
C. Dilute 1:10 with H2O and filter; perform TLC
for amphetamines
D. Titrate to pH 7.0, then follow procedure for
measuring amphetamine in urine
C. Dilute 1:10 with H2O and filter; perform TLC
for amphetamines
- SITUATION: Results of biochemistry tests are:
Na = 138 mmol/L
K = 4.2 mmol/L
Cl = 94 mmol/L
TCO2 = 20 mmol/L
glucose = 100 mg/dL
T bili = 1.2 mg/dL
BUN = 6.8 mg/dL
creat = 1.0 mg/dL
albumin = 4.8 g/dL
T protein = 5.1 g/dL
What should be done next?
A. Request a new specimen
B. Repeat the total protein
C. Repeat all tests
D. Perform a protein electrophoresis
B. Repeat the total protein
- The following chart compares the monthly total
bilirubin mean of Laboratory A to the monthly
mean of Laboratory B, which uses the same
control materials, analyzer, and method.
Both laboratories performed controls at the
beginning of each shift using commercially
prepared liquid QC serum stored at –20°C. Which
of the following conditions would explain these
differences?
A. Improper handling of the control material by
Laboratory A resulted in loss of bilirubin due to
photodegradation
B. The laboratories used a different source of
bilirubin calibrator
C. Laboratory B obtained higher results because its
precision was poorer
D. Carryover from another reagent falsely elevated
the results of Laboratory B
B. The laboratories used a different source of
bilirubin calibrator
- After installing a new analyzer and reviewing
the results of patients for 1 month, the lead
technologist notices a greater frequency of patients
with abnormally high triglyceride results. Analysis
of all chemistry profiles run the next day indicated
that triglyceride results are abnormal whenever the
test is run immediately after any sample that is
measured for lipase. These observations point to
which type of error?
A. Specificity of the triglyceride reagents
B. Precision in pipetting of lipemic samples
C. Bias caused by sequence of analysis
D. Reagent carryover
D. Reagent carryover
- SITUATION: A digoxin result from a stable
patient with a normal electrocardiogram (EKG)
is reported as 7.4 ng/mL (URL 2.6 ng/mL) using
an immunofluorescent method. Renal function
tests were normal and the patient was not taking
any other medications. The assay was repeated
and results were the same. The sample was
frozen and sent to a reference laboratory for
confirmation. The result was 1.6 ng/mL measured
by a competitive chemiluminescent procedure.
Which best explains the discrepancy in results?
A. The fluorescent immunoassay was performed
improperly
B. Digoxin was lower by the chemiluminescent
method because it is less sensitive
C. An interfering substance was present that
cross-reacted with the antibody in the
fluorescent immunoassay
D. Freezing the specimen caused lower results by
converting the digoxin to an inactive metabolite
C. An interfering substance was present that
cross-reacted with the antibody in the
fluorescent immunoassay
- The following results are reported on an adult
male patient being evaluated for chest pain:
What is the most likely cause of these results?
A. The wrong sample was assayed for the
first myoglobin
B. The patient did not suffer an MI until after
admission
C. Hemolysis caused interference with the 3-hour
and 6-hour myoglobin result
D. The patient is experiencing unstable angina
A. The wrong sample was assayed for the
first myoglobin
- Analysis of normal and abnormal QCs performed
at the beginning of the evening shift revealed a
22s error across levels for triglyceride. Both
controls were within the 3s limit. The controls
were assayed again, and one control was within
the acceptable range and the other was slightly
above the 2s limit. No further action was taken
and the patient results that were part of the run
were reported. Which statement best describes
this situation?
A. Appropriate operating procedures were followed
B. Remedial evaluation should have been taken,
but otherwise, the actions were appropriate
C. Corrective action should have been taken before
the controls were repeated
D. The controls should have been run twice before
reporting results
C. Corrective action should have been taken before
the controls were repeated
- A biochemical profile routinely performed
bimonthly on a renal dialysis patient showed a
decreased serum calcium and decreased PTH level.
Such a lab result may be explained by which of
the following circumstances?
A. Malignancy
B. Aluminum toxicity
C. Hypervitaminosis D
D. Acidosis
B. Aluminum toxicity
- Which set of the following laboratory results is most likely from a patient who has suffered an
AMI? Reference intervals are in parenthesis
B.
- Hemoglobin electrophoresis performed on agarose
at pH 8.8 gives the following results:
All components of the Hgb C, S, F, A control
hemolysate were within the acceptable range.
What is the most likely cause of this patient’s
result?
A. HgbLepore
B. Hgb S-β-thalassemia (Hgb S/β+)
C. Hgb SC disease post-transfusion
D. Specimen contamination
C. Hgb SC disease post-transfusion
- Two consecutive serum samples give the results
shown in the table above (at the top of this page)
for a metabolic function profile.
The instrument is a random access analyzer
that uses two sample probes. The first probe
aspirates a variable amount of serum for the
spectrophotometric chemistry tests, and the
second probe makes a 1:50 dilution of serum
for electrolyte measurements. What is the most
likely cause of these results?
A. Both patients have renal failure
B. There is an insufficient amount of sample in both
serum tubes
C. There is a fibrin strand in the probe used for the
spectrophotometric chemistry tests
D. The same patient’s sample was accidentally run
twice
C. There is a fibrin strand in the probe used for the
spectrophotometric chemistry tests
- SITUATION: A blood sample in a red-stoppered
tube is delivered to the laboratory for electrolytes,
calcium, and phosphorus. The tube is
approximately half full and is accompanied by a
purple-stoppered tube for a complete blood count
that is approximately three-quarters full. The
chemistry results are as follows:
What is the most likely explanation of these serum
calcium results?
A. Severe hemolysis during sample collection
B. Laboratory error in the calcium measurement
C. The wrong order of draw was used for vacuum
tube collection
D. Some anticoagulated blood was added to the
red-stoppered tube
D. Some anticoagulated blood was added to the
red-stoppered tube
- SITUATION: A patient previously diagnosed with
primary hypothyroidism and started on thyroxine
replacement therapy is seen for follow-up testing
after 2 weeks. The serum-free T4 is normal but the
TSH is still elevated. What is the most likely
explanation for these results?
A. Laboratory error in measurement of free T4
B. Laboratory error in measurement of TSH
C. In vitro drug interference with the free T4 assay
D. Results are consistent with a euthyroid patient in
the early phase of therapy
D. Results are consistent with a euthyroid patient in
the early phase of therapy
- SITUATION: A 6-year-old child being treated
with phenytoin was recently placed on valproic
acid for better control of seizures. After displaying
signs of phenytoin toxicity including ataxia,
a stat phenytoin is determined to be 15.0 mg/L
(reference range 10–20 mg/L). A peak blood level
drawn 5 hours after the last dose is 18.0 mg/L.
The valproic acid measured at the same time is
within therapeutic limits. Quality control is within
acceptable limits for all tests, but the physician
questions the accuracy of the results. What is the
most appropriate next course of action?
A. Repeat the valproic acid level using the last
specimen
B. Repeat the phenytoin on both trough and peak
samples using a different method
C. Recommend measurement of free phenytoin
using the last specimen
D. Recommend a second trough level be measured
C. Recommend measurement of free phenytoin
using the last specimen
- The results shown in the table above are
obtained from three consecutive serum samples
using an automated random access analyzer
that samples directly from a bar-coded tube.
Calibration and QC performed at the start of
the shift are within the acceptable range, and no
error codes are reported by the analyzer for
any tests on the three samples. Upon results
verification, what is the most appropriate course
of action?
A. Report the results and proceed with other tests
since no analytical problems are noted
B. Repeat the controls before continuing with
further testing, but report the results
C. Check sample identification prior to reporting
D. Do not report BUN results for these patients or
continue BUN testing
D. Do not report BUN results for these patients or
continue BUN testing
- An AFP measured on a 30-year-old pregnant
woman at approximately 12 weeks gestation is
2.5 multiples of the median (MOM). What
course of action is most appropriate?
A. Repeat the serum AFP in 2 weeks
B. Recommend AFP assay on amniotic fluid
C. Repeat the AFP using the same sample by
another method
D. Repeat the AFP using the sample by the same
method
A. Repeat the serum AFP in 2 weeks
- SITUATION: Biochemistry tests are performed
24 hours apart on a patient and delta-check
flag is reported for inorganic phosphorus by
the laboratory information system. Given the
results shown in the table above, identify the
most likely cause.
A. Results suggest altered metabolic status caused by
poor insulin control
B. The patient was not fasting when the sample was
collected on day 2
C. The samples were drawn from two different
patients
D. The delta-check limit is invalid when samples are
collected 24 or more hours apart
B. The patient was not fasting when the sample was
collected on day 2
- A quantitative sandwich enzyme immunoassay for
intact serum hCG was performed on week 4 and
the result was 40,000 mIU/mL (reference range
10,000–80,000 mIU/mL). The physician
suspected a molar pregnancy and requested that
the laboratory repeat the test checking for the
hook effect. Which process would identify this
problem?
A. Obtain a new plasma specimen and heat
inactivate before testing
B. Obtain a urine specimen and perform the assay
C. Perform a qualitative pregnancy test
D. Perform a serial dilution of the sample and repeat
the test
D. Perform a serial dilution of the sample and repeat
the test
- A patient presents to the emergency department
with symptoms of intoxication including impaired
speech and movement. The plasma osmolality was
measured and found to be 330 mOs/kg. The
osmolal gap was 40 mOsm/Kg. A blood alcohol
was measured by the alcohol dehydrogenase
method and found to be 0.15% w/v (150 mg/dL).
Electrolyte results showed an increased anion gap.
Ethylene glycol intoxication was suspected because
the osmolal gap was greater than could be explained
by ethanol alone, but gas chromatography was not
available. Which of the following would be
abnormal if this suspicion proved correct?
A. Arterial blood gases
B. Lactic acid
C. Urinary ketones
D. Glucose
A. Arterial blood gases
- Given the serum protein electrophoresis pattern
shown, which transaminase results would you
expect?
A. Within normal limits for both
B. Marked elevation of both (20–50-fold normal)
C. Mild elevations of both (2–5-fold normal)
D. Marked elevation of AST but normal ALT
C. Mild elevations of both (2–5-fold normal)
- Serial TnI assays are ordered on a patient at
admission, 3 hours, and 6 hours afterwards.
The samples were collected in heparinized
plasma separator tubes.
Following are the results
(reference range 0–0.03 μg/L)
Admission =0.03 μg/L
3 hours =0.07 μg/L
6 hours = 0.02 μg/L
These results indicate:
A. A positive test for acute myocardial infarction
B. Unstable angina
C. Cardiac injury of severity less than myocardial
infarction
D. Random error with the 3-hour sample
D. Random error with the 3-hour sample
