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25 Cards in this Set

  • Front
  • Back
In a normal Gaussian distribution, what percentage of the population falls between -2 and +2 standard deviations?
A. 68%
B. 90%
C. 95.5%
D. 99.7%
E. 99.9%
C. 95.5%.
For an ideal Gaussian distribution, the population is evenly distributed in a bell curve centered on the mean or mathematical average. That is, one half of the values are
above the center and one half below, with the greatest frequency occurring at the mean. The standard deviation is the average distance of any value from the mean. In a
Gaussian distribution, 68% of values lie between -1 and +1 standard deviation of the mean, 95.5% of values between -2 and +2 standard deviations, and 99.7% between -
3 and +3 standard deviations.
QCCP2, Gaussian distribution.
Which term describes the most frequently occurring variable in a range of values?
A. mean
B. standard deviation
C. median
D. mode
E. accuracy
D. mode.
Mean, median, and mode are three statistical terms that often pepper the conversation in a discussion of the distribution of values in a Gaussian population. Mean is the
arithmetic average of all the values - simply add up all the values and divide by the number of values. Median is the middle value among all values. The mode is the most
commonly occurring value. In a standard Gaussian distribution, the mean, median, and mode are all equal. In cases of skew, the mean, median, and mode may be
different.
QCCP2, Mean and standard deviation, Median, Mode.
Which of the following equations best describes the coefficient of variation?
A. !xi/n
B. ! (xi-mean)2/(n-1)
C. true positives/(true positives - false negatives)
D. standard deviation/mean " 100
E. true positives/(true positives + false positives)
D. standard deviation/mean ! 100.
When discussing test results, the concepts of accuracy and precision are frequently encountered and are often confused. Accuracy refers to how close a particular value is
to a gold standard reference value. Precision, however, is a description of how reproducible a particular result is. Precision can be mathematically expressed with the
coefficient of variation, which compares the deviation from the mean to the mean value, expressed as a percentage. CV = SD/mean ! 100.
QCCP2, Precision.
Which of the following are affected by pre-test probability? (you can choose more than one)
A. sensitivity
B. specificity
C. positive predictive value
D. negative predictive value
E. relative risk
C. positive predictive value, D. negative predictive value, E. relative risk.
Pretest probability is a function of the prevalence of a condition. When prevalence is high, the positive predictive value of a test is also usually high, while the negative
predictive value is low. When the prevalence of a disease is low, the opposite occurs - low PPV, high NPV. The relative risk is also affected by prevalence in a similar fashion.
QCCP2, PPV, Relative risk.
Which equation best describes sensitivity?
A. true positives divided by the sum of true positives plus false negatives
B. true negatives divided by the sum of true negatives plus false positives
C. true positives divided by the sum of true positives plus false positives
D. true negatives divided by the sum of true negatives plus false negatives
E. none of the above
A. true positives divided by the sum of true positives plus false negatives.
It's easy to get overwhelmed with terms when sensitivity and specificity are brought up. In essence, the sensitivity of a test is the ability of a test to rule out (you can use
the mnemonic, SnOUT) a disease. That is, a sensitive test is one that must be able to detect those that have the disease, so it makes sense that sensitivity is defined as the
number of people who test positive divided by the number of people who actually have the disease (true positives + false negatives). As a result, a sensitive test is an
excellent screening tool. On the other hand, a specific test is one that can “rule in” a disease (SpIN). Specificity is defined as the number of people who test negative for a
disease divided by the number of people WITHOUT the disease (true negatives + false positives). For this reason, a specific test is best used as a post-screening test to
differentiate false positives from true negatives.
QCCP2, Clinical sensitivity, Specificity.
What is the purpose of a receiver operating characteristic (ROC) curve?
A. to graphically determine the positive predictive value of a given test
B. to calculate the standard deviation of a set of values
C. to determine the prevalence of a particular condition
D. to measure the ability of a test to perform reliably
E. to determine the performance characteristics of a test at different cut-off values
E. to determine the performance characteristics of a test at different cut-off values.
If you would have used the classic test-taking skill of choosing the longest answer, you would have nailed this one. If you didn't, maybe the explanation will help. Plotting
sensitivity on the Y axis and 1-specificity on the X axis for a set of values, then connecting the values will generate a ROC curve. The purpose of the curve is to determine
the specificity or sensitivity of a test at any given value. As sensitivity increases, specificity decreases (or 1-specificity increases), leading to a curve. The area under the
curve is a function of the accuracy of the test.
QCCP2, Receiver operating characteristic (ROC) curves.
What is the most standardized definition of the reference interval for a test?
A. +/- 1 SD of the mean
B. +/- 2 SD of the mean
C. +/- 3 SD of the mean
D. sensitivity divided by specificity
E. a value calculated from the ROC curve
B. +/- 2 SD from the mean.
The central 95% of results (+/- 2 SD) obtained from healthy persons is most commonly used as the reference interval. This means that 5% of healthy individuals will have
values that fall out of the reference interval. In addition, a particular reference interval many not apply to another population.
QCCP2, Reference intervals.
All of the following are categories of CLIA-regulated lab tests, except:
A. waived tests
B. provider-performed microscopy
C. low complexity testing
D. moderate complexity testing
E. high complexity testing
C. low complexity testing.
Tests are listed in order of increasing CLIA regulation. Waived tests have the least regulation - follow manufacturer's instructions and good laboratory practices. Similarly,
provider-performed microscopy, such as ferning tests must also follow the same guidelines. The vast majority of standard laboratory tests fall under the moderate
complexity category. In addition to following the rules for waived tests, labs providing moderate complexity testing must have a standard operating procedure in addition to
performing and documenting calibration, controls, and quality control. High complexity testing must adhere to the same rules as moderate complexity testing but must also
document the validation of the assay, since most high complexity testing is created in house.
QCCP2, Quality control.
What is the purpose of a Levey-Jennings curve?
A. to calculate the mean of a new control sample
B. to calculate the standard deviation of a new control sample
C. to determine “in control” and “out of control” runs
D. all of the above
E. none of the above
D. all of the above.
Test runs are made with a new control sample to create a Levey-Jennings plot and determine the mean and standard deviation. From then on, the control is run on a
regular basis and the results are plotted on the Levey-Jennings plot created previously. The results of the plot are interpreted according to the Westgard rules to determine
if a test is “in control” or “out of control”.
QCCP2, Quality control.
All of the following are shorthand for Westgard rules, except:
A. 1:3s rule
B. 2:2s rule
C. R:4s rule
D. 4:1s rule
E. 10:10s rule
E. 10:10s rule.
The missing rule is the 10:mean rule. Each rule is a shorthand means of representation. The “s” in each stands for standard deviation, while the number preceding it stands
for the number of values. For example, the 1:3s rule states, “Is one value + or - 3 SD from the mean?”, the 2:2s rule: “Are 2 consecutive values + or - 2 SD on the same
side of the mean?” R:4s means, “Are any 2 values >4 SD from each other?” and 4:1s: “Are any 4 values >1 SD on the same side of the mean?”. Finally, the 10:mean rule
asks, “Are any 10 values on the same side of the mean?” Any run that violates one of the Westgard rules is labeled as “out of control.” The results from this run should not
be reported and the assay re-run.
QCCP2, Control specimens, The Westgard rules.
Which of the Westgard rules are most sensitive to random error (pick two)?
A. 1:3s rule
B. 2:2s rule
C. R:4s rule
D. 4:1s rule
E. 10:10s rule
A. 1:3s rule, C. R:4s rule.
The rules that address widening result distribution are more sensitive to random error. Drifting or shifting values imply a more systematic error and can be detected with
the other 3 Westgard rules, 2:2s, 4:1s, and 10:mean.
QCCP2, The Westgard rules.
Who is the final approving agency for proficiency testing as mandated by CLIA '88?
A. College of American Pathologists
B. Food and Drug Administration
C. American Society for Clinical Pathology
D. Department of Health and Human Services
E. American Association of Blood Banks
D. Department of Health and Human Services.
The HHS has the authority to recognize agencies as suitable providers of proficiency testing, while most of the other choices presented in the question represent some of those agencies authorized to provide such testing.
QCCP2, Proficiency testing
All the following are considered in calculating the standard deviation index that the College of American Pathologists uses for grading proficiency testing, except:
A. lab test result
B. lab reference intervals
C. mean for peer group
D. standard deviation for peer group
E. all of the above are used to calculate the standard deviation index
B. lab reference intervals.
Each participant in CAP's proficiency testing program is given a standard deviation index calculated by subtracting the lab result from the peer group. In general, the lab
must be within 2 standard deviations to be graded as acceptable. Greater than 3 standard deviations is considered unacceptable, while between 2 and 3 is regarded as
“needing improvement.”
QCCP2, Proficiency testing
Different kinds of bias are revealed with a correlation study. Which kind of bias is a cause of systemic variability?
A. constant (offset) bias
B. analytical bias
C. proportional bias
D. all of the above
E. none of the above
D. all of the above.
Constant bias and proportional bias are types of analytical bias. A constant bias is when the value of a new test is off from the standard assay by a predictable constant
amount. Proportional bias is when the difference between the two tests is non-linear. The analytical bias can also be mixed. If variability is random, then it cannot be
predicted accurately.
QCCP2, Analytical correlation.
All of the following are examples of tests where the analytical sensitivity of the test is extremely important, except:
A. troponin
B. D-dimer
C. microalbumin
D. human chorionic gonadotropin
E. all of the above are tests where analytical sensitivity is very important
E. all of the above are tests where analytical sensitivity is very important.
The analytical sensitivity of a test refers to the lowest analyte concentration detectable by the test. All of the tests mentioned share a common characteristic - very low
levels of the analyte may be clinically important. For this reason, it is very important to have a high analytical sensitivity for each of these tests.
QCCP2, Analytic sensitivity.
Which of the following scenarios poses the greatest risk of non-linearity?
A. samples with low analyte concentration
B. samples with high analyte concentration
C. mixed samples of several weak analytes
D. contaminated samples
E. none of the above
B. samples with high analyte concentration.
Typically assays are at the greatest risk of becoming non-linear at high analyte concentrations. In enzymatic assays, when the enzyme is fully saturated by substrate, the
rate of the reaction varies only with the concentration of the enzyme (remember that from Chapter 1?). Low analyte samples are at risk of pushing the analytic sensitivity
of an assay. Mixed and contaminated samples may pose other risks, such as interference.
QCCP2, Linearity.
Which of the following techniques is useful in avoiding heterophile antibody interference in an assay?
A. serial sample dilution
B. removal of immunoglobulins from a sample with polyethylene glycol
C. assay antibody modification
D. the use of specialized buffers
E. all of the above
E. all of the above.
Heterophile antibodies are interfering antibodies present in the sample that bind to the animal antibodies in the assay. Serial dilution will reveal the non-linear changes in
the assay due to heterophile antibodies vs. the expected linear changes in a true sample. All of the other techniques have been used to run assays once the presence of
heterophile antibodies is recognized.
QCCP2, Interference.
All of the following often increase with changes in posture from supine to sitting, except:
A. electrolytes
B. proteins
C. substances largely bound to proteins
D. formed elements, such as red blood cells
E. none of the above change in concentration with changes in posture
A. electrolytes.
Small molecules follow water when hydrostatic pressure increases and drives water into the interstitial space. Large molecules, such as proteins, and cells cannot.
Therefore, the concentration of the larger molecules and cells increases when water leaves.
QCCP2, Interference.
Which tube top color and additive are usually used for coagulation testing?
A. red, none
B. green, heparin
C. blue, citrate
D. black, buffered sodium citrate
E. lavender, EDTA
C. blue, citrate.
Each additive has its own special use. Obviously, a tube with no additive cannot be used for coagulation studies as it will likely clot prior to the assay being run on it.
Heparin is also a poor choice due to its potential effect on the assay. Samples collected in buffered sodium citrate are used for a fairly specific purpose - determining the
erythrocyte sedimentation rate. EDTA inhibits enzymatic assays, so samples containing it are used for non-enzymatic assays, such as obtaining cell counts. It is difficult to
remember the tube top colors, the specific additives, and the uses of each. To remember the colors and what additives are used, I put the tube top colors in the same order
as the colors of the rainbow - red, yellow, green, blue, purple (more about black and gray later).
Which tube top color and additive are usually used for coagulation testing?
A. red, none
B. green, heparin
C. blue, citrate
D. black, buffered sodium citrate
E. lavender, EDTA
Once the colors are arranged “rainbowically,” I use the mnemonic “NO
CHoiCE,” which stands for (respectively) none, citrate with dextrose, heparin, citrate, and EDTA. So red tube tops have no additive and therefore the sample will clot. You
know that won't be a useful sample for plasma chemistry, but will be useful for serum chemistry. Red tube tops are also used in the blood bank for antibody workups, and
for “serology” (remember serum is what's left behind when blood clots.). Yellow tube tops have citrate with dextrose. Remember from your blood banking, if you add
adenine to citrate and dextrose, you have one of the most common blood preservation additives. It stands to reason that samples collected in yellow tube tops are used in
the blood bank for cell-centered assays and are used for HLA testing. Samples in green tube tops have heparin added; therefore, the blood doesn't clot and the plasma can
be assayed.
Which tube top color and additive are usually used for coagulation testing?
A. red, none
B. green, heparin
C. blue, citrate
D. black, buffered sodium citrate
E. lavender, EDTA
For this reason, they are typically used for plasma chemistry applications. Citrate is an anticoagulant that does not interfere with enzymatic clotting assays and
that is why samples in blue tube tops are used. Finally, purple tube tops have EDTA. EDTA will inhibit enzymes, preventing clotting and proteolysis. Therefore the sample is
only used for non-enzymatic assays where an unclotted sample is necessary, such as obtaining cell counts. Black tube tops contain buffered sodium citrate and, as
mentioned previously, are used specifically for determination of erythrocyte sedimentation rates. Gray tube tops contain sodium fluoride, an enzyme inhibitor, and are used
primarily in the measurement of glucose. One can relate that if you don't brush the glucose off your teeth (using a toothpaste with fluoride), your teeth will turn gray.
Perhaps, too, that may help you to remember the use and additive of gray tube tops.
QCCP2, T8.1 Blood Collection Tubes.
Which phase(s) of testing account for the great majority of laboratory errors?
A. preanalytic
B. analytic
C. postanalytic
D. A & B
E. A & C
E. A & C.
Perhaps not a fair question, but something we in pathology should always remember. The majority of errors in testing occur outside the lab. We typically are very good at
controlling the analytical phase of the test with controls, quality assurance, proficiency testing, etc. However, we are not as good at controlling errors before the sample
arrives at the lab (labeling errors, ordering errors, collection errors, etc) and after the test is performed (delayed or inaccurate reporting, inappropriate response to results,
etc).
QCCP2, Errors in laboratory medicine.
Which of the following is typically NOT used in the calculation of the corrected (platelet) count increment?
A. pre-transfusion platelet count
B. post-transfusion platelet count
C. patient gender
D. body surface area
E. number of units of platelets given
C. patient gender.
The corrected count increment (CCI) measures the response of a patient's platelet count to a platelet transfusion. It is useful in determining whether a patient has platelet
refractoriness or not. The CCI is the change in platelet count (post-pre) multiplied by the patient's body surface area (sort of a substitute for the volume of distribution), all
divided by the actual number of platelets given. Ideally, if platelet refractoriness is suspected, the platelet count should be measured within an hour of transfusion and
again after 12-24 hours. (More in the hematology and blood bank chapters.)
QCCP2, Corrected (platelet) count increment.
What is the osmolal gap in a patient with a measured osmolarity of 311 mOsm/L, a sodium of 140, glucose of 180, and a blood urea nitrogen of 2.8?
A. 10
B. 20
C. 100
D. 200
E. 0
B. 20.
The osmolal gap is the difference between the measured osmolarity and the calculated expected osmolarity based on the concentration of the three major cellular
osmolytes - sodium, glucose, and blood urea nitrogen. In the calculation, each osmolyte is normalized for its respective contribution to osmolarity (more in Chapter 1). In
this case, the calculated osmolarity would be (140 ! 2) + (180/18) + (2.8/2.8) = 280 + 10 + 1 = 291. Subtracting that from the measured osmolarity of 311 gives 20.
QCCP2, Osmolal gap.
Which of the following is the correct Friedewald equation?
A. percent fetal cells " maternal blood volume = volume of fetal blood cells in maternal circulation
B. CCI = ([post-pre] " BSA)/# of units
C. pH = pKa + log ([base]/[acid])
D. CV = SD/mean " 100
E. LDL = total cholesterol - HDL - TG/5
E. LDL = total cholesterol - HDL - TG/5.
The Friedewald equation can be used to calculate the LDL from measured values of total cholesterol, HDL, and triglyceride.
QCCP2, Friedewald equation.