Chapter 10: Quality Control (Handout)

Question 1

a process to periodically examine a measurement procedure to verify that it is performing according to pre-established specifications

Answer 1

Quality Control

Question 2

Dispersion of results for repeated measurements of aliquots of the same QC material

Answer 2

Imprecision

Question 3

measure of expected imprecision in a measurement procedure when it is performing correctly

Answer 3

Standard Deviation

Question 4

Interval of ±1SD

Answer 4

68% of measured values

Question 5

Interval of ±2SD

Answer 5

95% of measured values

Question 6

Eliminates systematic bias

Answer 6

Correct Calibration

Question 7

Difference between the observed mean and the expected value for a QC material
- Brought about by changes in calibration

Answer 7

Systematic Bias

Question 8

• the combination of systematic bias and imprecision that occurred for that specific measurement

Answer 8

Accuracy

Question 9

refer to an average systematic bias that may be present in a given method

Answer 9

Trueness

Question 10

most often performed by the laboratory using calibrator materials provided by the method or instrument manufacturer

Answer 10

Method calibration

Question 11

methods are calibrated during the manufacturing process, and the laboratory performs a verification of that calibration

Answer 11

(E.g. Point-of-care devices)

Question 12

frequently specify calibration intervals

Answer 12

In vitro device (IVD) manufacturers

Question 13

Calibration of routine methods should be traceable to a higher-order reference measurement procedure or international reference material

Answer 13

Calibration Traceability to a Reference System and Commutability Considerations

Question 14

• evaluates a measurement procedure by periodically assaying a QC sample for which the expected result is known in advance.
• part of the process management component of the quality system that integrates good laboratory practices to ensure correct patient results.

Answer 14

Statistical QC

Question 15

Most common presentation for evaluating QC results

Answer 15

Levey- Jennings or Shewhart Plot

Question 16

±1SD

Answer 16

68.3% of observations

Question 17

±2SD

Answer 17

95.4% of observations

Question 18

±3SD

Answer 18

99.7% of observations

Question 19

Selection of QC Materials

Answer 19

Two different concentrations are necessary for adequate statistical QC
- Analyte concentrations that monitor the analytic measurement range of the method, should be selected for Quantitative Methods

Question 20

Frequency to Assay Quality Control Samples

Answer 20

Analytic stability of the measurement procedure

• Risk of harm to a patient from clinical action being taken before a significant error is detected
• Number of patient results produced in a period of time when an error condition existed but was not yet detected
• Events such as recalibration or maintenance that may alter the current performance condition of the measurement system
• Training and competency of the test operator, particularly for manual or semi-automated methods
• Risk of failure of the measuring device

Question 21

Establishing Quality Control Target Value and Standard

Deviation That Represent a Stable Measurement Operating Condition

Answer 21

• a minimum of 20 observations is recommended for the initial SD estimate
• determine the SD for stable measurement performance from the cumulative SD over a 6- to 12-month period for a single lot of QC material.

Question 22

➔ commonly used to assess how well a method performs relative to the medical requirement.
➔ Compares the variability in a measurement process (in SD) vs. the acceptable variability because it will not cause an error diagnosis or treatment of a patient

Answer 22

Sigma Metric

Question 23

➔ conventional way to express QC interpretive rules is by using an abbreviation nomenclature popularized among clinical laboratories

Answer 23

Westgard Rules

Question 24

Corrective Action When a Quality Control Result

Indicates a Measurement Problem

Answer 24

• A QC alert occurs when a QC result fails an
  evaluation rule, which indicates that an analytic
  problem may exist.
• There is a high probability that the assay is
  producing results unreliable for patient care

Question 25

Reviewing Quality Control Data

Answer 25

Immediate impact of QC data is to determine if patient results can be reported and used for clinical decision making

Question 26

Weekly by Senior Technologist/and or Supervisors

Answer 26

- Ensure that correct follow-up of any QC alerts was conducted - Patient samples that may have had erroneous results were repeated - Ensure that process was properly documented in QC records

Question 27

Monthly by Laboratory Director

Answer 27

- Address/Include any issues identified by the weekly review process - Examination of the Levey-Jennings chart* or other tool to identify trends or changes in assay performance that may need to be addressed - Review consistency of reagent lot changes, calibrator lot changes, and any patient data–based QC procedures

Question 28

Major Function of the QC Review Process

Answer 28

o It verifies that test procedures are stable and meet performance specifications, o Identifies test procedures that may need intervention to address trends in performance deterioration

Question 29

recommends 3 or more samples

Answer 29

CLSI document EP26

Question 30

Alternate

Answer 30

10 or more patient samples that span the analytic measurement range and use Deming regression analysis

Question 31

Results from patient samples support QC processes in a laboratory by verification of

Answer 31

o Consistency of patient results when changing lots of reagent or calibrators for a method o Identified inconsistent results using a delta check with a previous result for a patient o Consistency of patient results when an analyte is measured using more than one instrument or method in a health care system o Method performance using results from patient samples in a statistical QC scheme

Question 32

Delta Check with a Previous Result for a Patient

Answer 32

o Comparing a patient’s current test result to a previous result for the same analyte o Most useful to detect mislabeled samples and samples altered by dilution with IV fluid during collection from a patient

Question 33

Clinical patient sample aliquots are assayed using each of two or more methods (or analyzers) to evaluate, and if necessary adjust the calibration as needed, to achieve agreement in results for patient samples

Answer 33

Round Robin

Question 34

Automated approaches to determine the mean (or median) for groups of sequential patient results

Answer 34

Average of Normals (AON)/ Moving Average

Question 35

A program to evaluate method performance by comparison of results versus those of other laboratories for the same set of samples

Answer 35

Proficiency Testing or External Quality Assessment

Question 36

Proficiency Testing or External Quality Assessment

Answer 36

o Each laboratory assays the PT samples as if they were patient samples and reports the results for the PT samples to the PT provider for evaluation o The PT provider assigns a target value to the PT samples and determines if the results for an individual laboratory are in close enough agreement with the target value o PT allows a laboratory to verify that its results are consistent with those of other laboratories and to verify that it is using a method in conformance with the manufacturer’s specifications.