Quality Assurance and Quality Control.pdf

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

Documents

Quality Assurance and Quality Control.pdf