QUALITY CONTROL Flashcards
Quality Management
Refers to the overall process used to ensure
that laboratory results meet the requirement
for health care services to patients.
Quality management system
- Organization and leadership
- Customer focus
- Facilities and safety
- Personnel
- Supplier and inventory
- Equipment
- Process management
* Pre examination
* Examination (measurement)- Validation/verification
- Quality control
- Post examination
- Documents and records
- Information management
- Nonconforming event
- Assessments
- Continual improvement
Quality Control
- It is a process that ensures the
reproducibility and accuracy of results by
utilizing control specimens or by ensuring
that a method remains valid over time. - It is a system for ensuring precision and
accuracy in the laboratory by utilizing
quality control reagents in each series of
measurements. - It is part of the Quality Management System.
Analytic Bias and Imprecision:
Imprecision?
- Dispersion of result for repeated
measurements of aliquots of the same quality
control material. - Calibrate whenever new reagents are
used.
Functions of Quality Control: Serves as a reference for the proper operation
of equipment, reagents, and individual
techniques.
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o Machine stability
o Reagent quality
o Error detection
Functions of Quality Control
1. ?
2. ?
3. ?
4. ?
5. ?
- Serves as a reference for the proper operation
of equipment, reagents, and individual
techniques.
o Machine stability
o Reagent quality
o Error detection - Compared the testing’s accuracy when
compared to reference values. - Recognizes an increase in the frequency of
both excessively high and excessively low
minimally acceptable values (dispersion). - Detects any progressive drift of values away
from the average value over a period of at
least 2 days (trends). - Exhibits an abrupt shift or change in value
from the established average value for three
consecutive days (shift).
Difference between QC and Calibration?
Quality control is done daily while
calibration is done weekly/monthly etc.
Step by step operation of Quality Control process.
- Determining the statistical margins of error
for each analytic method. - Using these criteria to evaluate the quality
control data generated for each test. - Correcting error as necessary
a) Identifying the causes of the error
b) Taking corrective action
c) Reanalyzing control and patient data
Analytic Bias and Imprecision: Standard Deviation (SD)
- Measure of expected imprecision in a
measurement procedure when its performing
correctly (measure of size of the distribution) - Interval of ± 1SD – 68% of measured values
- Interval ± 2SD – 95% measured values
- Correct calibration of method
eliminates systemic biases.
Analytic Bias and Imprecision: Systemic Bias
- Difference between the observed mean and
the expected value for a Quality Control
material - Brought by the changes in calibration
Analytic Bias and Imprecision: Accuracy
- The combination of systemic bias and
imprecision that occurred for that specific
measurement.
Analytic Bias and Imprecision: Trueness
- Refer to an average systemic bias that
may be present in a given method.
Calibration consideration in Quality Control
Calibration of the analytic measurement
procedure is a key component in achieving
quality result.
Type of Control Used in Clinical Laboratory
- Assaved control
- Un-assaved control
- Homemade control
Type of Control Used in Clinical Laboratory: Assaved control
- The value of analyte is predetermined.
- Most commercially available controls
have predetermined values of various
analytes - The target value must be verified before
use
Type of Control Used in Clinical Laboratory: Un-assaved Control
- The target value is not predetermined
- This control must be fully validated
- Run at least 20 times in a single run and then
run once a day for 20 consecutive days to
establish a target value.
Type of Control Used in Clinical Laboratory: Homemade Control
- Prepared by the laboratory staff
- Pure material in an aqueous-based solvent
(dissolved and weighed correctly) or in serum
or whole blood (for an analyte not present in
humans, e.g. drug).
Overview of Quality Control Procedures: Statistical Quality Control
- Evaluates a measurement procedure by
periodically assaying a Quality control
sample for which the expected result is
known in advance. - Parts of the process management component
of the quality system that integrates good
laboratory practices to ensure correct patient
results.
Levey-Jennings/ Shewhart plot
- Most common presentation for evaluating
quality control results. - The number of results expected within the
Standard Deviation intervals is as follows:
Must be at the mean to be accepted
±1 SD = 68.3% of observations (accepted)
±2 SD = 95.4% of observation (not accepted)
±3 SD = 99.7% of observations (not
accepted)
Implementing Quality Control Procedures: Selection of Quality control materials
- Two different concentrations are necessary
for adequate statistical Quality Control - Analyte concentrations that monitor the
analytic measurement range of the method,
should be selected for Quantitative methods.
Frequency to assay quality control samples
- 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.
Establishing quality control target value and
Standard deviation that represents a stable
measurement operating conditions
- A minimum of 20 observation is
recommended for the initial Standard
deviation estimate - Determine the Standard deviation for stable
measurement performance from the
cumulative Standard deviation over a 6- 12
month period for a single Quality control
material
Performance of a measurement procedure for its intended medical use: Sigma Metric
- Commonly used to assess how well a
method performs relative to the
medical requirement - Compares the variability I a
measurement (in SD) VS the
acceptable variability because it will
not cause an error diagnosis or
treatment of a patient.
Establishing rules to evaluate quality control
results: Westgard Rules
- Conventional way to express quality
control interpretative rules is by using
an abbreviation nomenclature
popularized among clinical
laboratories - CUSUM and EWMA – preferred to
monitor for bias trends
o CUSUM- Cumulative Sum
o EWMA- Exponentially Weighted
Moving Average
Corrective action when a quality control result
indicates a measurement problem.
1.
2.
- A quality control alert occurs when a Quality
control 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
Reviewing Quality control Data
- Immediate impact of Quality control data is
determined if patient results can be
reported and used for clinical decision
making. - Review Schedules of Quality Control data
PURPOSE: Weekly (Senior Technologist and Supervisors)
- Ensure that correct follow-up of any
QC alerts was conducted - Patients sample may have had
erroneous results were repeated - Ensure that process was properly
documented in Quality Control
records
PURPOSE: Monthly (Laboratory Director)
- Address/ include any issues identified
by the weekly review process - Examination of the Levey-Jennings
chart or other tool to identify trends or
changed 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.
Major Functions of the QC Review process
o It verifies that test procedures are
stable and meets performance
specifications.
o Identifies test procedures that may
need intervention to address trends in
performance deterioration.
Reagent and Calibrator Lot Changes
- Changing reagent lots can have an
unexpected impact on QC results - Use of clinical samples to verify the
consistency of results between old and new
lots of reagents is necessary - CLSI document EP26 (CLSI, 2013)
recommends 3 or more samples - Alternate: 10 or more patient
samples that span the analytic
measurement range and use Deming
regression analysis
Using patient Data in QC Procedures: Results from patient sample support QC process in a laboratory by verification of:
o Consistency of patient results when
changing lots of reagents or
calibrators 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 sample in a statistical QC
scheme.
Delta Check with a Previous Result for a
Patient
o Comparing a patient’s current test
results to a previous result for the
same analyte.
o Most useful detect mislabeled
samples and samples altered by
dilution with IV fluid during
collection from a patient
Round Robin
- 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.
Using Patient Data for statistical Quality
control
o Patient results can be used to monitor
method performance
o Not widely adopted because of lack of
consensus guidelines for use and lack
of computer support from instrument
and LIS suppliers.
Average of Normals (AON) / Moving
Average
Þ Automated approaches to determine
the mean (or median) for groups of
sequential patient results
Proficiency Testing/ External Quality Assessment
- A program to evaluate method performance
by comparison of results versus those of other
laboratories for the same set of samples.
o Each laboratory assays the Proficiency
testing samples as if they were patient
samples and reports the results for the
Proficiency testing samples to the
Proficiency provider for evaluation.
o The PT provider assigns a target value
to the PT sample and determines if he
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 methods in conformance
with the manufacturer’s specification.
Common Causes for PT Failure
- Clerical errors
- Methodological problems.
- Equipment problems
- Technical problems caused by personnel errors
- A problem with the PT material.
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