Question 1

The precision limits of a method are defined by

Accepted Answer

Evaluating the same specimen multiple times and applying statistics to the results determine precision or reproducibility.The SD describes the precision.The mean is the average result (assuming a gaussian distribution).Sensitivity describes how well a test identifies positive patients,whereas specificity is how well it identifies only positive patients.

Question 2

A clinical laboratory scientist performs 30 replicate hemoglobin determinations on a single blood sample.When statistics are used to determine the precision of the method,the mean is 13.8 g/dL and 1 SD is 0.1 g/dL.This means that 95.5% of the results on this specimen lie

Accepted Answer

Because 1 SD is 0.1 g/dL,2 SD = 0.2 g/dL.Thus 95.5% of the results lie between 13.6 (±2 SDs)and 14.0 (+2 SDs).

Question 3

Which of the following groups of patients should not be included in establishing moving averages using red cell indices?

Accepted Answer

Chemotherapeutic drugs often interfere with DNA metabolism,and this affects the mean cell volume (MCV)and mean cell hemoglobin (MCH),two of the red cell indices used in the moving averages determination.These patients thus should not be used when setting up this method as a quality control tool.It is also true that,when using moving averages as part of a quality control program,an out of control situation often occurs when a group of 20 patients includes primarily oncology patients.

Question 4

One of two controls that have been evaluated over the last 28 days gives a result on day 29 between 2 and 3 SDs of the mean;the other control is within 2 SDs of its mean.What is the correct procedure to follow?

Accepted Answer

One control is acceptable,whereas the other is a warning that the method may be going out of control.The test option in this case is to repeat the analysis of the control,and if it is acceptable,continue with patient analysis,reporting the results.The instrument does not appear to need recalibration because one control is acceptable and the other is within 3 SDs (1 result of 20 can acceptably be within ±3 SDs).If the repeat on the "out of control" vial is still out between 2 and 3 SDs,then a new vial of that control should be opened and analyzed.The control that was acceptable does need to be repeated.

Question 5

Which of the following is true regarding reference ranges?

Accepted Answer

Reference ranges should be determined by evaluating a group of perhaps as many as 120 normal healthy people for the same analyte.If the analyte differs in different groups,based on data such as age and sex,it must be determined for each group if at all possible.

Question 6

The antinuclear antibody (ANA)test is positive in almost all people who have systemic lupus erythematosus (SLE).It is also positive in some patients who do not have SLE.The antideoxyribonucleic acid (anti-DNA)test is positive only in people with SLE but not in all who do.Which of the following is true?

Accepted Answer

Because almost all patients with SLE have a positive ANA test,it is a good screening test (if the result is negative,it practically rules out this diagnosis for a patient).However,because the ANA test is also positive in other patients,the anti-DNA test is a good confirmatory test,because only patients with SLE have a positive result.In practice,the ANA test is done first;if it is positive,then the anti-DNA test is done as follow-up.If a patient is positive with both tests,then his or her diagnosis is SLE.

Question 7

The best way to prevent errors in the laboratory is to

Accepted Answer

Only well-trained,conscientious clinical laboratory personnel can ensure that the best-quality results are routinely obtained for patients.A high-quality instrument is effective only when it is correctly calibrated and maintained.Management,although ultimately responsible,relies on the laboratory personnel to be aware of potential problems in assays.External quality control programs do not guarantee the daily validity of patient results.

Question 8

A laboratory gets numerous complaints regarding the length of time it takes hematology results to get to the emergency department.What would be an appropriate response?

Accepted Answer

Quality assurance evaluates the process from the time a test is ordered until it is reported to the correct patient chart.One of the responsibilities a clinical laboratory has is to get results to physicians and other caretakers in a timely manner;the acceptable turnaround time (TAT)for a particular procedure will vary depending on the reason it is ordered.Obviously,an emergency department has a need for rapid TAT.Complaints from caregivers should never be ignored;it probably is not reasonable to tell employees to work faster,and explaining why it takes so long will not help provide good patient care.

Question 9

A purchased hemoglobin standard is used to adjust a hemoglobinometer.This standard is being used as a

Accepted Answer

Standards are used to calibrate instruments.Controls are used to routinely evaluate the accuracy of a method once it is calibrated.Precision is a measure of reproducibility,whereas delta checks compare a patient result with a previous result (same test on the same patient).This can only be done for a test result that essentially does not vary significantly from testing time to testing time.

Question 10

A patient specimen is analyzed on an instrument known to be in control from previous assays performed on a calibrated instrument and gives a hemoglobin result of 13.2 g/dL.Two hours later it is evaluated on another instrument that is being evaluated for purchase by the laboratory.The result is 11.8 g/dL.This result,when compared with the first,is

Accepted Answer

This result is inaccurate compared with the first because it is significantly different.Precision is not known,because multiple results are needed to determine precision;in addition,precision must be determined using the same instrument,not between instruments.Because it is not accurate,it cannot be reported.

Question 11

The control values for both controls for the prothrombin test were ranging between the mean and ±1 SD for the first 19 days of use.Starting on day 20,the values for both were consistently between +1 and +2 SDs.This is an example of a

Accepted Answer

If all results are consistently different from the previous in the same direction,it indicates a shift in the methodology has occurred.A trend would show a gradual change over time.This is neither a predictable error nor a random error because it is consistent.

Question 12

A patient's white blood cells (WBCs)are counted on an automated cell counter 10 times.The mean white count is 8000/mL,and the standard deviation (SD)is 300.What is the coefficient of variation (CV)?

Accepted Answer

% CV = (SD/mean) x 100 = (300/8000)x100 = 3.8%

Question 13

The following hemoglobin results,reported in g/dL,are obtained on a hospitalized patient on 3 consecutive days:
$\frac{\text { Day 1 }}{14.3} \quad \frac{\text { Day } 2}{11.5} \quad \frac{\text { Day } 3}{144}$
The SD for this hemoglobin method was calculated in Question 18.A delta check was obtained on day 2.Controls were run as appropriate each day and were all within limits for this procedure.
What is the most probable reason for the day 2 result when compared with those for days 1 and 3?

Accepted Answer

The significant drop in hemoglobin from day 1 to day 2, followed by an unusually high value on day 3, suggests a possible error in patient identification or sample handling on day 2.

Question 14

Proper specimen collection and patient satisfaction are components of

Accepted Answer

Quality assurance encompasses everything from the test order by the physician to the reporting of results to the correct patient chart.Quality control involves running control samples using the same methodology as for the patient specimens.Reliability is how well a method maintains both accuracy and precision over time.Precision is the ability to reproduce a result on the same specimen.

Question 15

The tubing that brings the lyse reagent to the hemoglobin cuvette on an automated cell counter is pinched and not delivering any reagent.All hemoglobin values are greater than 20 g/dL.This represents what type of error?

Accepted Answer

A constant systematic error is one in which the magnitude of the error remains the same throughout the range of the test measurement.The error is proportional if the magnitude varies relative to the result.This is not a random error,which happens only infrequently and is not predictable.Precision requires multiple measurements of the same specimen and evaluates the ability to consistently reproduce the result.

Question 16

What does the CV calculated in Question 2 describe about the white cell counts?

Accepted Answer

The CV is a measure of precision,or how well a result can be reproduced.It allows comparisons of assays with different means and is a unitless number,although usually expressed as a percentage.Accuracy is how close a result is to the true value;proper calibration is required to obtain accuracy.Reliability is how well a method holds both accuracy and precision over time.

Question 17

A laboratory comparing its results to those of other laboratories on the same specimen is an example of

Accepted Answer

When results are compared with those of another laboratory,this is part of external quality control.Internal quality control is done totally within one laboratory.Delta checks compare a patient result with a previous result on the same patient.Precision is determined by multiple analysis of the same specimen.

Question 18

Which of the following would most likely be associated with the situation described in Question 11?

Accepted Answer

Shifts can occur when a new reagent is introduced.A fading light source would lead to trend error.If the instrument were calibrated incorrectly,both controls should be out;likewise,operator error would result in both controls being unacceptable.

Question 19

A test that is positive in all patients who have the disease but also in some who do not have the disease is

Accepted Answer

Sensitivity (diagnostic)is defined by the number of people with the disease who test positive.In this case,all patients with the disease have a positive result,so the test is very sensitive.The test,however,is not specific because it is also positive in some people who do not have the disease.Reliability refers to the performance stability of a test over time.Precision evaluates reproducibility of the result if repeated multiple times on a specimen.

Quiz 5: Quality Assurance in Hematology and Hemostasis Testing