1. Unit #7 - Basic Quality Control for the Clinical Laboratory
Cecile Sanders, M.Ed., MT(ASCP),
CLS (NCA)

2. Unit #7 - Basic Quality Control for the Clinical Laboratory
Introduction
The results obtained from laboratory analyses are used to diagnose, prescribe treatment, and/or monitor the health or progress of the patient. Since such importance is placed upon test results, they must be as reliable and accurate as possible.

3. Unit #7 - Basic Quality Control for the Clinical Laboratory
Elements of a Total Quality Control Program (may be referred to as QC, QA, or TCM, among others)
Current procedure manual
Documentation
Qualified personnel
Fire and safety program
Use of appropriate standards and controls
External proficiency testing

4. Unit #7 - Basic Quality Control for the Clinical Laboratory
Standards and Controls
Standard
A substance that has an exact known value and that, when accurately weighed or measured, can produce a solution of an exact concentration
Also called “reference materials”
Not usually used on a daily basis
Used to calibrate new instruments, recalibrate instruments after repair, at manufacturer’s recommended intervals, or if a method is out of control

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A solution that contains the same constituents as those being analyzed in the patient sample
Most are commercially produced from pooled sera
The manufacturer has analyzed each lot of serum for a variety of test components and the expected range of assay values for each component is provided to the laboratory when shipped

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Control (cont’d)
Controls are analyzed with each patient test or batch of tests and the results are compared with the manufacturer’s range of values
For most tests, a “normal” control and an “abnormal” control are analyzed with each patient test or batch of tests
Results are plotted on a QC record called a Levey-Jennings Chart

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Example of Levey-Jennings Chart

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Accuracy - closeness of a result to the actual value
Precision – “reproducibility” or closeness of values to each other

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Mean, Variance and Standard Deviation – these must be determined for each test or analysis to be used for quality control
Mean ( ) = the average for a set of values
Standard Deviation (s or SD) = a measure of the scatter of the sample values around the mean and is derived from the calculation of the variance (s2)

11. Unit #7 - Basic Quality Control for the Clinical Laboratory
Calculating the variance

12. Unit #7 - Basic Quality Control for the Clinical Laboratory
Using Standard Deviation in QC
When a set of values with a normal distribution is plotted on a graph, the distribution of the values around the mean forms a Gaussian Curve (also known as a normal frequency or normal distribution curve)

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Using Standard Deviation in QC (cont’d)
Clinical laboratories establish the standard deviation for each laboratory test or analysis
A common choice is plus or minus 2 s or SD, most often written as ± 2 s or ± 2 SD

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The mean and ± 2 SD are plotted on a Levey-Jennings chart (green line is )

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Every time the control is run, the value is plotted on the L-J chart

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As long as the control value are between the ± 2 SD lines on the L-J chart (in this case, the lines are colored yellow), the control values are “in control”

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On the L-J chart below, note that values for days 5, 8, 11, 17, 25, and 27 are outside the ± 2 SD yellow lines. Therefore, controls on these days are “out of control”

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Levey-Jennings Chart with Values “In Control”

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Trend
An uninterrupted rise or decline away from the mean
When the 6th value with a rise or decline is reached, the values are “out of control”

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Shift
An uninterrupted shift of values on one side of the mean
When the 6th value on one side of the mean is reached, the values are “out of control”

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The use of a single control is for very basic laboratory testing in waived CLIA laboratories
In moderately and highly complex CLIA testing laboratories two controls (usually a “normal” and an “abnormal”) must be run with each test or batch of tests and Westgard Rules apply
Westgard Rules are beyond the scope of this course and will be covered in advanced MLT courses

22. Unit #7 - Basic Quality Control for the Clinical Laboratory
Whenever a patient’s test or a batch of tests are performed and the control(s) is “in control”, the values obtained for the patient test(s) are determined to be “acceptable” and can be released to the doctor as accurate.
Whenever a patient’s test or a batch of tests are performed and the control(s) is “out of control”, the values obtained for the patient test(s) are determined to be “not acceptable” and CANNNOT be released to the doctor as accurate until the problem is identified and resolved.

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Errors in Laboratory Testing
May occur at several points
Preanalytical – errors made prior to testing the patient specimen (Ex. Misidentifying the patient during blood collection, mishandling specimen, etc.)
Analytical – errors made in the testing process (Ex. Error in procedure, instrument trouble, etc.)
Postanalytical – errors made after testing (Ex. Typing the wrong results in the computer, failure to notify physician in a timely manner, etc.)

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Errors in Laboratory Testing (cont’d)
Random or Systematic
Random Errors – cannot be absolutely identified (Ex. Differences in techniques between workers, specimen characteristics, etc.)
Systematic Errors – variation that may make results consistently higher or lower than the mean value for a control (Ex. Trouble with the instrument, deteriorated reagents, etc.)

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Errors in Laboratory Testing (cont’d)
Our goal is to identify systematic errors and eliminate them!
My control results are “out of control”! Now what?

26. Unit #7 - Basic Quality Control for the Clinical Laboratory
The following steps should be taken in order when the control results are “out of control”
Look at the procedure and evaluate your technique (Ex. Did I use the right lot #? Are my reagents in date? Did I make an error in the procedure?)
Re-run the procedure, including controls
If results are still out of control, clean/perform maintenance on equipment and/or open a new batch of reagents
Contact supervisor

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ALWAYS, ALWAYS, ALWAYS:
DOCUMENT THE PROBLEM AND CORRECTIVE ACTIONS TAKEN!!!!!

28. Unit #7 - Basic Quality Control for the Clinical Laboratory
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