Clinical Chemistry-Calculations, QC and Statistics Flashcards by H. JG

How many grams of sodium hydroxide (NaOH)
are required to prepare 150.0 mL of a 5.0% w/v
solution?
A. 1.5 g
B. 4.0 g
C. 7.5 g
D. 15.0 g

C. 7.5 g

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How many milliliters of glacial acetic acid are
needed to prepare 2.0 L of 10.0% v/v acetic acid?
A. 10.0 mL
B. 20.0 mL
C. 100.0 mL
D. 200.0 mL

D. 200.0 mL

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A biuret reagent requires preparation of a stock
solution containing 9.6 g of copper II sulfate
(CuSO4) per liter. How many grams of CuSO4* 5H2O are needed to prepare 1.0 L of the stock
solution?
Atomic weights: H = 1.0; Cu = 63.6; O = 16.0; S = 32.1
A. 5.4 g
B. 6.1 g
C. 15.0 g
D. 17.0 g

C. 15.0 g

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How many milliliters of HNO3 (purity 68.0%,
specific gravity 1.42) are needed to prepare 1.0 L
of a 2.0 N solution?
Atomic weights: H = 1.0; N = 14.0; O = 16.0
A. 89.5 mL
B. 126.0 mL
C. 130.5 mL
D. 180.0 mL

C. 130.5 mL

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Convert 10.0 mg/dL calcium (atomic weight = 40.1)
to International System of Units (SI).
A. 0.25
B. 0.40
C. 2.5
D. 0.4

C. 2.5

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Convert 2.0 mEq/L magnesium (atomic
weight = 24.3) to milligrams per deciliter.
A. 0.8 mg/dL
B. 1.2 mg/dL
C. 2.4 mg/dL
D. 4.9 mg/dL

C. 2.4 mg/dL

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How many milliliters of a 2,000.0 mg/dL glucose
stock solution are needed to prepare 100.0 mL of a
150.0 mg/dL glucose working standard?
A. 1.5 mL
B. 7.5 mL
C. 15.0 mL
D. 25.0 mL

B. 7.5 mL

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What is the pH of a solution of HNO3, if the
hydrogen ion concentration is 2.5 × 10–2 M?
A. 1.0
B. 1.6
C. 2.5
D. 2.8

B. 1.6

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Calculate the pH of a solution of 1.5 × 10–5 M
NH4OH.
A. 4.2
B. 7.2
C. 9.2
D. 11.2

C. 9.2

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How many significant figures should be reported
when the pH of a 0.060 M solution of nitric acid
is calculated?
A. 1
B. 2
C. 3
D. 4

B. 2

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What is the pH of a 0.05 M solution of acetic
acid? Ka = 1.75 × 10–5, pKa = 4.76
A. 1.7
B. 3.0
C. 4.3
D. 4.6

B. 3.0

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What is the pH of a buffer containing 40.0 mmol/L
NaHC2O4 and 4.0 mmol/L H2C2O4? (pKa = 1.25)
A. 1.35
B. 2.25
C. 5.75
D. 6.12

B. 2.25

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A solvent needed for HPLC requires a 20.0 mmol/L phosphoric acid buffer, pH 3.50, made by mixing KH2PO4 and H3PO4. How many grams of
KH2PO4 are required to make 1.0 L of this
buffer?
Formula weights: KH2PO4 = 136.1; H3PO4 = 98.0;
pKa H3PO4 = 2.12
A. 1.96 g
B. 2.61 g
C. 2.72 g
D. 19.2 g

B. 2.61 g

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A procedure for cholesterol is calibrated with
a serum-based cholesterol standard that was
determined by the Abell–Kendall method to
be 200.0 mg/dL. Assuming the same volume
of sample and reagent are used, calculate the
cholesterol concentration in the patient’s sample from the following results.

A. 123 mg/dL
B. 172 mg/dL
C. 232 mg/dL
D. 314 mg/dL

B. 172 mg/dL

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A glycerol kinase method for triglyceride calls for a
serum blank in which normal saline is substituted
for lipase in order to measure endogenous glycerol.
Given the following results, and assuming the
same volume of sample and reagent are used for
each test, calculate the triglyceride concentration
in the patient’s sample.
A. 119 mg/dL
B. 131 mg/dL
C. 156 mg/dL
D. 180 mg/dL

B. 131 mg/dL

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A procedure for aspartate aminotransferase (AST)
is performed manually because of a repeating error
code for nonlinearity obtained on the laboratory’s
automated chemistry analyzer; 0.05 mL of serum
and 1.0 mL of substrate are used. The reaction rate
is measured at 30°C at 340 nm using a 1.0 cM
light path, and the delta absorbance (-ΔA) per
minute is determined to be 0.382. Based upon a
molar absorptivity coefficient for NADH at
340 nm of 6.22 X 103 M–1 cM–1 L–1, calculate
the enzyme activity in international units (IUs)
per liter.
A. 26 IU/L
B. 326 IU/L
C. 1228 IU/L
D. 1290 IU/L

D. 1290 IU/L

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When referring to quality control (QC) results,
what parameter usually determines the acceptable
range?
A. The 95% confidence interval for the mean
B. The range that includes 50% of the results
C. The central 68% of results
D. The range encompassed by ±2.5 standard
deviations

A. The 95% confidence interval for the mean

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Which of the following quality control (QC) rules
would be broken 1 out of 20 times by chance alone?
A. 1_2s
B. 2_2s
C. 1_3s
D. 1_4s

A. 1_2s

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Which of the following conditions is cause for
rejecting an analytical run?
A. Two consecutive controls greater than 2 s above
or below the mean
B. Three consecutive controls greater than 1 s above
the mean
C. Four controls steadily increasing in value but less
than ±1 s from the mean
D. One control above +1 s and the other below –1 s
from the mean

A. Two consecutive controls greater than 2 s above
or below the mean

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One of two controls within a run is above +2s
and the other control is below –2s from the mean.
What do these results indicate?
A. Poor precision has led to random error (RE)
B. A systematic error (SE) is present
C. Proportional error is present
D. QC material is contaminated

A. Poor precision has led to random error (RE)

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Two consecutive controls are both beyond –2s
from the mean. How frequently would this occur
on the basis of chance alone?
A. 1:100
B. 5:100
C. 1:400
D. 1:1,600

D. 1:1,600

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The term R4S means that:
A. Four consecutive controls are greater than ±1
standard deviation from the mean
B. Two controls in the same run are greater than
4s units apart
C. Two consecutive controls in the same run are
each greater than ±4s from the mean
D. There is a shift above the mean for four
consecutive controls

B. Two controls in the same run are greater than
4s units apart

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A trend in QC results is most likely caused by:
A. Deterioration of the reagent
B. Miscalibration of the instrument
C. Improper dilution of standards
D. Electronic noise

A. Deterioration of the reagent

In most circumstances, when two controls within a
run are both greater than ±2s from the mean, what
action should be taken first?
A. Recalibrate, then repeat controls followed by
selected patient samples if quality control is
acceptable
B. Repeat the controls before taking any corrective
action
C. Change the reagent lot, then recalibrate
D. Prepare fresh standards and recalibrate

A. Recalibrate, then repeat controls followed by
selected patient samples if quality control is
acceptable

25. When establishing QC limits, which of the following practices is inappropriate? A. Using last month’s QC data to determine current target limits B. Exclusion of any QC results greater than ±2s from the mean C. Using control results from all shifts on which the assay is performed D. Using limits determined by reference laboratories using the same method

B. Exclusion of any QC results greater than ±2s from the mean

26. Which of the following assays has the poorest precision?

27. Given the following data, calculate the coefficient of variation for glucose. A. 3.0% B. 4.6% C. 7.6% D. 33.0%

A. 3.0%

28. Which of the following plots is best for detecting all types of QC errors? A. Levy–Jennings B. Tonks–Youden C. Cusum D. Linear regression

A. Levy–Jennings

29. Which of the following plots is best for comparison of precision and accuracy among laboratories? A. Levy–Jennings B. Tonks–Youden C. Cusum D. Linear regression

B. Tonks–Youden

30. Which plot will give the earliest indication of a shift or trend? A. Levy–Jennings B. Tonks–Youden C. Cusum D. Histogram

C. Cusum

31. All of the following are requirements for a QC material except: A. Long-term stability B. The matrix is similar to the specimens being tested C. The concentration of analytes reflects the clinical range D. Analyte concentration must be independent of the method of assay

D. Analyte concentration must be independent of the method of assay

32. Examine the Levy–Jennings chart at the bottom of the previous page and identify the QC problem that occurred during the first half of the month. A. Shift B. Trend C. Random error D. Kurtosis

B. Trend

33. Referring to the Levy–Jennings chart, what is the first day in the month when the run should be rejected and patient results should be repeated? A. Day 6 B. Day 7 C. Day 8 D. Day 9

C. Day 8

34. Referring to the Levy–Jennings chart, what analytical error is present during the second half of the month? A. Shift B. Trend C. Random error D. Kurtosis

A. Shift

35. What is the first day in the second half of the month that patient results would be rejected? A. Day 16 B. Day 17 C. Day 18 D. Day 19

B. Day 17

36. Given the following QC chart, identify the day in which a violation of the R4s QC rule occurs. A. Day 3 B. Day 8 C. Day 10 D. Day 15

D. Day 15

37. What is the minimum requirement for performing QC for a total protein assay? A. One level assayed every 8 hours B. Two levels assayed within 8 hours C. Two levels assayed within 24 hours D. Three levels assayed within 24 hours

C. Two levels assayed within 24 hours

38. Which of the following statistical tests is used to compare the means of two methods? A. Student’s t test B. F distribution C. Correlation coefficient (r) D. Linear regression analysis

A. Student’s t test

39. Two freezing point osmometers are compared by running 40 paired patient samples one time on each instrument, and the following results are obtained: If the critical value for F = 2.8, then what conclusion can be drawn regarding the precision of the two instruments? A. There is no statistically significant difference in precision B. Osmometer A demonstrates better precision that is statistically significant C. Osmometer B demonstrates better precision that is statistically significant D. Precision cannot be evaluated statistically when single measurements are made on samples

A. There is no statistically significant difference in precision

40. Two methods for total cholesterol are compared by running 40 paired patient samples in duplicate on each instrument. The following results are obtained: Assuming the samples are collected and stored in the same way and the analysis done by a technologist who is familiar with both methods, what is the bias of method y? A. 0.4 B. 7.2 C. 10.6 D. 11.0

D. 11.0

41. When the magnitude of error increases with increasing sample concentration, it is called: A. Constant error B. Proportional error C. Random error D. Bias

B. Proportional error

42. Which explanation is the best interpretation of the following BUN bias plot? A. The new method consistently overestimates the BUN by a constant concentration B. The new method is greater than the reference method but not by a statistically significant margin C. The new method is lower than the reference method by 5 mg/dL D. The new method is lower than the reference and the magnitude is concentration dependent

D. The new method is lower than the reference and the magnitude is concentration dependent

43. Serum samples collected from hospitalized patients over a 2-week period are split into two aliquots and analyzed for prostate specific antigen (PSA) by two methods. Each sample was assayed by both methods within 30 minutes of collection by a technologist familiar with both methods. The reference method is method × (upper reference limit = 4.0 μg/L). Linear regression analysis was performed by the least-squares method, and results are as follows: Which statement best characterizes the relationship between the methods? A. There is a significant bias caused by constant error B. There is a significant proportional error C. There is no disagreement between the methods because the correlation coefficient approaches 1.0 D. There is no systematic error, but the random error of the new method is unacceptable

A. There is a significant bias caused by constant error

44. Which statement best summarizes the relationship between the new BUN method and reference method based upon the following linear regression scatterplot? A. The methods agree very well but show a high standard error of estimate B. There is little or no constant error, but some proportional error C. There will be a significant degree of uncertainty in the regression equation D. There is significant constant and proportional error but little random error

B. There is little or no constant error, but some proportional error

45. A new method for BUN is evaluated by comparing the results of 40 paired patient samples to the urease-UV method. Normal and high controls were run on each shift for 5 days, five times per day. The results are as follows: What is the total analytical error estimate for a sample having a concentration of 50 mg/dL? A. –2.2 mg/dL B. –2.8 mg/dL C. –7.5 mg/dL D. –10.0 mg/dL

C. –7.5 mg/dL

46. In addition to the number of true negatives (TN), which of the following measurements is needed to calculate specificity? A. True positives B. Prevalence C. False negatives D. False positives

D. False positives

47. A new tumor marker for ovarian cancer is evaluated for sensitivity by testing serum samples from patients who have been diagnosed by staging biopsy as having malignant or benign lesions. The following results were obtained: Number of malignant patients who are positive for CA 125 = 21 out of 24 Number of benign patients who are negative for CA 125 = 61 out of 62 What is the sensitivity of the new CA 125 test? A. 98.4% B. 95.3% C. 87.5% D. 85.0%

C. 87.5%

48. A new test for prostate cancer is found to have a sensitivity of 80.0% and a specificity of 84.0%. If the prevalence of prostate cancer is 4.0% in men over 42 years old, what is the predictive value of a positive test result (PV+) in this group? A. 96.0% B. 86.0% C. 32.4% D. 17.2%

D. 17.2%

49. What measurement in addition to true negatives and prevalence is required to calculate the predictive value of a negative test result (PV–)? A. False negatives B. Variance C. True positives D. False positives

A. False negatives

50. A laboratory is establishing a reference range for a new analyte and wants the range to be determined by the regional population of adults age 18 and older. The analyte concentration is known to be independent of race and gender. Which is the most appropriate process to follow? A. Determine the mean and standard deviation of the analyte from 40 healthy adults and calculate the ±2s limit B. Measure the analyte in 120 healthy adults and calculate the central 95th percentile C. Measure the analyte in 120 healthy adults and use the lowest and highest as the reference range limits D. Measure the analyte in 60 healthy adults and 60 adults with conditions that affect the analyte concentration; calculate the concentration of least overlap

B. Measure the analyte in 120 healthy adults and calculate the central 95th percentile

51. When comparing the laboratory’s monthly mean to its peer group to determine if bias is present, what statistic is most appropriate? A. F test B. Linear regression analysis C. Correlation coefficient D. Standard deviation index

D. Standard deviation index

52. Which of the following methods is most useful in order to detect sample misidentification? A. Cumulative summation B. Critical limit C. Delta limit D. Significant change limit

C. Delta limit

53. Which of the following total quality management tools can be used to calculate the analytical error rate for an analyte in the clinical laboratory? A. LEAN B. Six sigma C. ISO 9000 D. Laboratory information system

B. Six sigma

54. In which circumstances is a validation study (versus performing routine quality control) required? A. Instrument recalibration B. Source lamp or ion selective electrode change C. Change in reagent lot D. Change in calibrator lot

C. Change in reagent lot

55. The following plot represents a study of a screening test for malignant prostate cancer using plasma PSA (ng/mL). The outcome measured was positive cytology results obtained by biopsy. What concentration gives the highest sensitivity with the last number of unnecessary biopsies ? A. 2.6 B. 3.6 C. 3.8 D. 5.2

B. 3.6