basics of laboratory internal quality control, ola elgaddar

7/30/2019 Basics of Laboratory Internal Quality Control, Ola Elgaddar

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Ola H. ElgaddarMBChB, MSc, MD, CPHQ

Lecturer of Chemical PathologyMedical Research Institute

Alexandria [email protected]


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Total Quality Management (TQM)

- A continuous approach that seeks to

improve quality and performance which

will meet or exceed customer

expectations.

- This can be achieved by integrating allquality-related functions and processes

throughout the organization.

- TQM requires the involvement of

everyone; management, workforce,suppliers, and customers (feedback)

- Divided into four sequential

categories: plan, do, check, and actthe PDCA c cle


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In a medical lab, we have three

main stages that need control:

1) Pre-analytical

2) Analytical3) Post-analytical

All of them should be under tight control


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1) Pre-analytical:

Patient & specimen identification

Patient preparation

Specimen collection, transport and handling Monitoring personnel


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2) Analytical:

Internal quality control (IQC)

External quality assessment (EQA)


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IQC is used, on daily basis, in the decision to

accept or reject results of patients samplesand enables the lab to describe and monitor

the quality of its work.

EQA permits a comparison of quality between

laboratories and thus describes the state of

the art for that area of laboratory work

encompassed by the EQA program .

It is used to confirm results of IQC


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3) Post-analytical:

Transcriptional errors

Unclear report format or information


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IQC procedures

A stable control material which mimicspatients sample is analyzed(day to day)

Individual measurements are plotted on acontrol chart (Levey Jennings charts)

Evaluationwhether measurement is incontrol (Westgard multi-rules)


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Control material

IFCC defines control material as a solutionanalyzed solely for Q.C. purpose and not for

calibration

Criteria to be considered:

1. Matrix

2. Reconstitution 3. Stability

4. Assayed or un assayed

5. Appropriate analyte level


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1) Matrix:

-BASE from which the control material isprepared.

-Ideally the same matrix as specimen so thatthey behave like a specimen.

- Controls available are HUMAN BASED orBOVINE BASED


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2) Reconstitution:

Liquid / lyophilized (Liquid controls better) Reconstitution material

Quantity of solvent (volume?)

Mixing

Waiting (when to use the reconstitutedcontrol)

Vial to vial variation

(Standardization of these factors necessary)


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3) Stability:

Expiry date and stability after reconstitutionshould be considered

Desirable is one year supply of the samelot, so that the lab can have its own QCrange for a longer period of time.


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4) Assayed / Un-assayed QC:

Assayed QC material are the usually usedtype in our labs

They have manufacturer values for eachinstrument / method

Those values should be considered asguidelines only till each lab establish its ownQC range

Minimum period of time for a lab to

establish its own range is 20 days Ideally, a new QC lot should be run, hand in

hand with the old lot, its values areestablished before it is run routinely.


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5) Appropriate analyte level

The used QC material should be coveringthe measured range of the analyte, both inits normal and pathological range.

It is preferable to have a control value nearthe medical decision level.

Ideally, there are two levels of QC materialused in Chemistry analysis and three levelsfor hormones and tumor markers.


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Plotting QC result onLevey Jennings control chart

Mean and SD of QC material (manufactureror each labs values)

Y-axis: control value Vs X-axis: time of run

Most autoanalyzers plot the charts,

otherwise they should be drawn manually

A chart is plotted for each control level


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Evaluating QC results usingWestgard rules

Detects whether results are in control ornot.

Detects the type of laboratory error


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Random error, RE, or imprecision isdescribed as an error that can be eitherpositive or negative, whose direction andexact magnitude cannot be predicted,

where the distribution of results whenreplicate measurements are made on asingle specimen.

Usually, due to error in pippetting


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Systematic error, SE, or inaccuracy is an

error that is always in one direction,displacing the mean of the distribution fromits original value.

In contrast to random errors, systematicerrors are in one direction and cause all thetest results to be either high or low.

Eitherconstant orproportionate

Usually, due to error in calibration


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1 reading exceeding 2 SD

Warning


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1 reading exceeding 3 SD

Random error

Rejection


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2 readings exceeding 2 SD

Systematic error

Rejection


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4 readings exceeding 1 SD, on one side of mean

Systematic error

Rejection


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10 readings on the same side of the mean

Systematic error

Rejection


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2 readings, their sum exceeds 4 SD

Random error

Rejection


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basics of laboratory internal quality control, ola elgaddar

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