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Clinical Chemistry- Clinical Chemistry Problem Solving Flashcards

(50 cards)

1
Q
  1. 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
A

C. Add 5.0 mg of glucose to 1.0 mL of a serum of
known concentration and measure

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2
Q
  1. 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

A. The instrument giving the highest absorbance for
a solution of 0.1 mmol/L NADH at 340 nm

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3
Q
  1. 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
A

D. Report the undiluted ion selective electrode
result

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4
Q
  1. 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
A

B. Chemical interference caused incomplete
atomization

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5
Q
  1. 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

A

B. Drug or alcohol intoxication

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6
Q
  1. 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
A

C. Examine the reference electrode junction for salt
crystals

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7
Q
  1. 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

A. 8.5

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8
Q
  1. 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
A

B. Request a new specimen and repeat the
glycosylated Hgb

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9
Q
  1. 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

A

C. Runs 1, 2, and 3

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10
Q
  1. 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
A

C. Blood for peak level was drawn too soon

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11
Q
  1. 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

A

D. Blood gas sample was exposed to air

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12
Q
  1. 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

A

D. TCO2

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13
Q
  1. 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

A. Sample drawn above an IV

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14
Q
  1. 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

A

B. The accident caused traumatic injury, but no
heart attack occurred

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15
Q
  1. 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

A

B. Check the albumin, total protein, Ca, P, and
Mg results; if normal, repeat the sodium test

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16
Q
  1. 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
A

C. Call for a new specimen

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17
Q
  1. 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

A

B. Water contamination of the column packing

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18
Q
  1. 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

A

B. Report the amylase as 720 U/L

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19
Q
  1. 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

A. Report results along with an estimate of the
degree of hemolysis

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20
Q
  1. 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
A

B. Uric acid, BUN, creatinine

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21
Q
  1. 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
A

B. Less recovery from sample 2 occurred in the
extraction step

22
Q
  1. 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
A

C. Prepare fresh developing solvent and repeat
the assay

23
Q
  1. 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
A

C. High levels of reducing substances interfering
with the Trinder reaction

24
Q
  1. 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

A

D. Excess release of ferritin caused by injury

25
25. 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
26
26. 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
27
27. 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
28
28. 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
29
29. 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
30
30. 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
31
31. 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
32
32. 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
33
33. 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
34
34. 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
35
35. 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
36
36. 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
37
37. 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
38
38. Which set of the following laboratory results is most likely from a patient who has suffered an AMI? Reference intervals are in parenthesis
B.
39
39. 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
40
40. 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
41
41. 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
42
42. 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
43
43. 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
44
44. 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
45
45. 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
46
46. 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
47
47. 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
48
48. 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
49
49. 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)
50
50. 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