The document discusses quality assurance of laboratory test results based on ISO/IEC 17025. It discusses the importance of analytical measurement data and ensuring results are accurate and precise. It describes internal quality control procedures like spikes, blanks, and replicates that analysts use to ensure results are correct. It also discusses external quality assurance like participating in inter-laboratory comparisons and proficiency testing schemes. The document emphasizes that laboratories must have quality control procedures to monitor validity of tests and ensure trends in results are detectable.

1. Quality Assurance of Laboratory
Test Results
based on ISO/IEC 17025
1

2. Hamidreza Dehnad
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3. The three pillars of Quality
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4. Analytical Measurement’s Data
• Analytical results are basis upon which economic,
ecological, legal decisions are made
• (i.e. International food trade)
• Results must be of certain quality :
▫ Accuracy
▫ Known uncertainty
▫ Compatible with other analytical measurements
• Overall aim of Quality Control is to ensure that the
results are of adequate accuracy and precision

5.  Quality Control (QC) is the combination of
systems, procedures, instructions and activities
that are performed to control and maintain work
quality
 One of the most important elements of QC is to
make a method perform reproducibly
Quality Control

6.  Internal quality control comprises the routine practical
procedures that enable the analytical chemist to
 accept a result or group of results as fit for purpose
 reject the results and repeat the analysis
 Quality control is what analysts do to ensure
their results are correct
Internal Quality Control

7.  Internal Quality Control includes:
 “spikes” (fortification or recovery samples)
 blank samples (reagent/matrix blanks)
 replicate or triplicate measurements (injections)
 System Suitability Tests
 usage of different analytical standards
 measurements on two different instruments
 measurements by two analysts
 application of different analytical method
 etc.
Internal Quality Control

8.  External Quality Control comprises participation of
the laboratory in appropriate inter-laboratory comparison.
It includes:
 laboratory comparison
 “round robin” tests, ring tests
 proficiency testing schemes
 collaborative studies
 “bench – marking”
External Quality Assurance

9. 9
Assuring the Quality of Test and Calibration
Results - ISO/IEC 17025 – 5.9
• The laboratory shall have quality control
procedures for monitoring the validity of tests
and calibrations undertaken.
• The resulting data shall be recorded in such a
way that trends are detectable and, where
practicable, statistical techniques shall be
applied to the reviewing of the results.

10. 10
Assuring the Quality of Test and Calibration
Results - ISO/IEC 17025 – 5.9
• This monitoring shall be planned and reviewed
and may include, but not be limited to, the
following:
▫ regular use of certified reference materials and/or
internal quality control using secondary reference
materials;
▫ participation in interlaboratory comparison or
proficiency-testing programmes;
▫ replicate tests or calibrations using the same or
different methods;
▫ retesting or recalibration of retained items;
▫ correlation of results for different characteristics of
an item.

11. Interaction of 5.9 with other
paragraphs
• What are the basic principles underlying the
lab‘s dealing with out‐of‐control‐results (4.9)?
• How are the records kept on such situations
(4.13/4.9)?
• Who is responsible (4.9)?
• Have corrective actions been necessary (4.11)?
• Was the cause analysis done properly (4.11)?
• Was any preventive action identified (4.12)?
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12. Variables that affect the quality of
results
 The educational background and training of the
laboratory personnel
 The condition of the specimens
 The controls used in the test runs
 Reagents
 Equipment
 The interpretation of the results
 The transcription of results
 The reporting of results

13. Types of “error”
• Systematic
▫ Error that can be corrected e.g. by applying
correction factors from calibration certificates
▫ Inadequate design, malfunctions, technician
blunders or technique, matrix effect, etc.
• Random
▫ We should try to correct for the error
▫ Any error source we don’t know is a source of
uncertainty and is inherent to the object being
measured

14. Accuracy vs. Precision
A BC D

15. Repeatability and Reproducibility
• Repeatability – within run precision
• Reproducibility – between-run precision

16. Types of “error”
• Systematic error affect accuracy – proximity to the
true value
 Error that can be corrected e.g. by applying correction
factors from calibration certificates
 Inadequate design, malfunctions, technician blunders or
technique, matrix effect, etc.
• Random error affect precision – spread of the
results around the mean
 We should try to correct for the error
 Any error source we don’t know is a source of uncertainty
and is inherent to the object being measured

17. Bias – Trueness – Systematic error
• Bias is the closeness of agreement
between the true value or if not
known, the accepted reference
value, and the expectation or the
mean result which is obtained
when the experimental procedure
is applied a large number of times
(= systematic error).
Reference
Value
Average
Test result
-
Bias

18. Precision – Reproducibility – Random Error
• The closeness of agreement between
independent test results obtained by
applying the experimental procedure
several times under stipulated
conditions (= random error).
• The measure of precision is usually
expressed in terms of imprecision and
calculated as a standard deviation of
the test results. Less precision is
reflected by a larger standard
deviation.
Precision
True
value

19. Is our method biased?
• a – biased (inaccurate) result (too
low precision?)
• b - accurate with high precision
• c - accurate with low precision
a
b
c
 

20. Random and Systematic Errors
Random Systematic
Affect precision Affect accuracy
Within run precision –
repeatability
Proximity to the truth –
bias - trueness
Between run precision –
reproducibility
Indeterminate error Determinate error

21. Accuracy vs. Precision

22. QC approaches
• Depend on the nature of work of the laboratory
Concerned:
Large batches of similar materials
Large batches of samples of widely differing
matrix or determinant concentration
Wide variety of different tests in small
batches
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23. Elements of QC Mechanism
• Blank / Background
• In-house RM (control sample)
• Duplicate analysis
• Replicate analysis
• Certified Reference Material
• Spike sample
• Participation in a Proficiency test
• Phantom (Ghost) sample
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24. Statistical techniques
• Control Charts
• Critical Difference Evaluation
• Significance tests
• ….
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25. 25

26. ?
QUESTIONS
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