A simple introduction to internal quality control

1. Basics of laboratory quality control
Ola H. Elgaddar
MBChB, MSc, MD, CPHQ
Lecturer of Chemical Pathology
Medical Research Institute
Alexandria University
Ola.elgaddar@alex-mri.edu.eg

2. 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 all
quality-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 act

3. In a medical lab, we have three
main stages that need control:
1) Pre-analytical
2) Analytical
3) Post-analytical
All of them should be under tight control

4. 1) Pre-analytical:
• Patient & specimen identification
• Patient preparation
• Specimen collection, transport and handling
• Monitoring personnel

5. 2) Analytical:
• Internal quality control (IQC)
• External quality assessment (EQA)

6. IQC is used, on daily basis, in the decision to
accept or reject results of patients samples
and 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

7. 3) Post-analytical:
• Transcriptional errors
• Unclear report format or information

8. IQC procedures
• A stable control material which mimics
patient’s sample is analyzed (day to day)
• Individual measurements are plotted on a
control chart (Levey Jennings charts)
• Evaluation whether measurement is “in
control” (Westgard multi-rules)

9. Control material
IFCC defines control material as a solution
analyzed 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

10. 1) Matrix:
-BASE from which the control material is
prepared.
-Ideally the same matrix as specimen so that
they behave like a specimen.
- Controls available are HUMAN BASED or
BOVINE BASED

11. 2) Reconstitution:
• Liquid / lyophilized (Liquid controls better)
• Reconstitution material
• Quantity of solvent (volume?)
• Mixing
• Waiting (when to use the reconstituted
control)
• Vial to vial variation
(Standardization of these factors necessary)

12. 3) Stability:
• Expiry date and stability after reconstitution
should be considered
• Desirable is one year supply of the same
lot, so that the lab can have its own QC
range for a longer period of time.

13. 4) Assayed / Un-assayed QC:
• Assayed QC material are the usually used
type in our labs
• They have manufacturer values for each
instrument / method
• Those values should be considered as
guidelines only till each lab establish its own
QC 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 are
established before it is run routinely.

14. 5) Appropriate analyte level
• The used QC material should be covering
the measured range of the analyte, both in
its normal and pathological range.
• It is preferable to have a control value near
the medical decision level.
• Ideally, there are two levels of QC material
used in Chemistry analysis and three levels
for hormones and tumor markers.

15. Plotting QC result on
Levey Jennings control chart
• Mean and SD of QC material (manufacturer
or each lab’s 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

17. Evaluating QC results using
Westgard rules
• Detects whether results are “in control” or
not.
• Detects the type of laboratory error

18. • Random error, RE, or imprecision is
described as an error that can be either
positive or negative, whose direction and
exact magnitude cannot be
predicted, where the distribution of results
when replicate measurements are made on
a single specimen.
• Usually, due to error in pippetting

19. • Systematic error, SE, or inaccuracy is an
error that is always in one
direction, displacing the mean of the
distribution from its original value.
• In contrast to random errors, systematic
errors are in one direction and cause all the
test results to be either high or low.
• Either constant or proportionate
• Usually, due to error in calibration

21. 1 reading exceeding 2 SD
Warning

22. 1 reading exceeding 3 SD
Random error
Rejection

23. 2 readings exceeding 2 SD
Systematic error
Rejection

24. 4 readings exceeding 1 SD, on one side of mean
Systematic error
Rejection

25. 10 readings on the same side of the mean
Systematic error
Rejection

26. 2 readings, their sum exceeds 4 SD
Random error
Rejection