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7/29/2019 Quality Assurance and Quality Control.pdf
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Quality Assurance and Quality
Control
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QUALITY CONTROL
It is a system ofensuring precision and
accuracy in the laboratory by using quality
control reagents in every series of
measurements.
It is a system of techniques to ensure with a
specified degree of confidence that the result
obtained from each series of analysis is trueand correct.
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Three phases of quality assurance
Pre-analytical phase
Preparation
e.g. labeling of tubes
Analytical phase
Main focus of quality control
Should be done properly and correctly
Post-analytical phase
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Implications of Quality Control
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Sensitivity
The ability of a method to detect and measure eventhe smallest amount of the particular substancetested for.
It is also the degree by which significant deviations
can be detected Analytical sensitivity able to measure minute
concentration of the analyte
Diagnostic sensitivity the test must always give a
(+) result in the presence of the diseaseTrue (+)
= ------------------------------- x 100
True (+) + False (-)
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Specificity
The ability of a method to measure only thecomponent desired without the interference of someother substances present in the same sample.
Analytical specificity
able to measure only oneunknown substance
Diagnostic specificity the test must always give anegative result in the absence of disease
True (-)= ------------------------------- x 100
True (-) + False (+)
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Accuracy
The ability of a method to determine the exact
value of the substance of interest in the
sample.
It is the closeness or the nearness of a test
value (value obtained) to the original value
(pre-determined value)
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Precision and Reproducibility
The ability of a method to give repeated
results on the same sample that agrees with
one another.
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Practicality
The degree by which a method is easily
repeated.
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Other purposes of Quality Control
To check the stability of the machine
To check the quality of reagents
To check for technical error if any wascommitted by the operator
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Tools of Quality Assurance and Quality
Control
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Standard solution
For accuracy
A solution of known characteristics and ofknownvalue or whose concentration is accurately known
It is composed of one known constituent only andused as a basis of reference for the calculation of thevalue of the unknown.
100% pure
Serve as a reference for unknown Choose the standard nearest to the unknown
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Control solution
For precision
The material (either commercially or non-
commercially prepared) with physical &
chemical properties closely resembling the
test
Derived from human blood
Pooled serum (1yr)
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Blank
Solution without the specimen
With reagent
Set the reading to zero For accuracy
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Two kinds of Quality Control reagents
Commercially prepared
Manufactured by different companies which may come in
the lyophilized (pulverized, dried or powdered) and the
non-lyophilized (liquid) form
Types:
Assayed values are known and given
Unassayed values are known but not given
Non-commercially prepared Sources for the preparation of non-commercially prepared
QC reagents
Left-over sera (pooled sera)
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VARIATIONS
Errors in Quality Control
The fundamental basis of any statistical
analysis
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TYPES:
Random
Due to unpredictable cause
Systematic
Due to definite cause
Aging phenomena variations due to reagents
Personal bias variations cause by operator
Clerical
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STATISTICAL CONCEPTS DEALING WITH MOST
PROBLEMS OF VARIATIONS
Arithmetic Value or Mean or average (x) The mathematical result when the summation of data is divided by
the total number of data
Standard Deviation (SD) It is the statement of the extent of variation in any series of
measurement It is a measure of the distribution range of values around the mean
value or average
Coefficient of Variation (CV) It is the percentile expression of the mean which is measure of the
relative magnitude of variability. It is the ratio of the standard deviation over the mean expressed in
percent
Variance (V) It is a statement of variability and measures the significant
differences between groups of data.
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PREPARATION OF QUALITY CONTROL CHARTS
(HISTOGRAMS)
Shewhart-Levey Jennings Chart Most commonly used
Also referred as a Levey-Jenning chart, S-L/J
Also known as dot chart
Gaussian Curve
It will group any series of measurement in the same sample in a cluster around the
mean in a bell shaped curve Also known as Gaussian distribution curve, normal distribution curve and commonly
the bell-shaped curve.
Cumulative Sum Graph
Plotted with the accumulated differences from the mean of individual values with themiddle value being zero.
Also referred as the CUSUM graph
Youden Plot A 2-mean chart drawn at right angles to one another with the one set of values on
one axis another set of values on the other axis.
Also referred to as the Twin plot, Two-Mean chart or the Two-way Average chart.
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INTERPRETATION OF RESULTS:
In control when the values of the control fall
within the confidence limit
Out of control when the values of the
control fall outside the confidence limit.
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Types of Out of Control Charts
Trend
It is formed by the control values that continue either to increase ordecrease for a period of six (6) consecutive days by passing the mean.
It indicates usually a deteriorating reagent or changes in the concentrationof standards.
Shift
It is formed by the control values that distribute themselves on one side ofthe mean for a period of six (6) consecutive days. Often deterioration ofstandard will cause a shift.
Outliers
Are values which are far from the main set of values due to wild errors
Conditions when dealing with outliers:
1 outlier in 20 days (in control) 2 or more outlier in 20 days (out of control)
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Types of Quality Control Program
External Quality Control program Proficiency
testing
Internal Quality Control program or
Intralaboratory Quality Control program
establish reference values in the laboratory.
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BENEFITS OBTAINED FROM A QUALITY
CONTROL PROGRAM
Provision of a continuous record of reliability of laboratoryresults
Permits valid judgments on the accuracy of results bymonitoring precision and permitting comparisons assayvalues on known control sera with stated values.
Gives early warning of trends and shifts in control results sothat remedial actions may be taken before serious loss ofprecision.
Monitors the performance and stability of equipment usedion the assay.
Allows a comparison between different techniques for the
assay of a substance, and thus, derive a choice betweenmethods Establish confidence on the part of the technologist when
making a report on the result.
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PRACTICAL CONSIDERATIONS IN QUALITY
CONTROL PROGRAM:
Specimen collection and handling
Reagents and equipment
Methods and procedures Standards and controls
Qualified personnel