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Unit #6 - Basic Quality Control for the Clinical Laboratory. Cecile Sanders, M.Ed., MLS(ASCP). Unit #6 - Basic Quality Control for the Clinical Laboratory. Introduction

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Unit #6 - 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.


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Unit #6 - 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


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Unit #6 - 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Control

    • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Accuracy - closeness of a result to the actual value

  • Precision – “reproducibility” or closeness of values to each other



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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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)



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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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • The mean and ± 2 SD are plotted on a Levey-Jennings chart (green line is ;  2 SD are yellow lines)


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Unit #6 - Basic Quality Control for the Clinical Laboratory

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


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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Levey-Jennings Chart with Values “In Control”


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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Trend

    • An uninterrupted rise or decline away from the mean

    • When the 6th value with a rise or decline is reached (Day or Run #10 on this graph), the values are “out of control”


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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Shift

    • An uninterrupted shift of values on one side of the mean

    • When the 6th value on one side of the mean is reached (Day or Run #10 on this graph), the values are “out of control”


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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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

  • http://www.westgard.com/mltirule.htm


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Unit #6 - 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • 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?


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Unit #6 - 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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Unit #6 - Basic Quality Control for the Clinical Laboratory

ALWAYS, ALWAYS, ALWAYS:

DOCUMENT THE PROBLEM AND CORRECTIVE ACTIONS TAKEN!!!!!


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Unit #6 - Basic Quality Control for the Clinical Laboratory

  • Click on the “Assignments” button on the lower left of the menu for the assignment for this unit.

  • Remember this is an ASSIGNMENT, so you may use all instructional materials to complete the assignment, including this PowerPoint.


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