Inter-laboratory comparisons and proficiency testing are important techniques for assessing the competence of accredited laboratories and ensuring accurate and reliable results, as outlined in ISO/IEC 17025 and 17043 standards. These programs involve laboratories analyzing the same or similar samples and their results being statistically evaluated to check performance both within individual labs and between labs. The goal is to validate testing and calibration procedures, identify any issues, and improve quality across participating laboratories.

1. INTER-LAB COMPARISON/
PROFICIENCY TESTING
Awot Gebre-egziabher
MSC
BPHARM

2. CONSEQUENCES
OF ANALYTICAL ERRORS
DECISIONS
Food toxicity
(e.g.. dioxins)
Environmental
pollution
(e.g. drinking water)
Medical diagnosis,
forensic science
Industrial products
(e.g. impact on trade)

3.  The competence of accredited
laboratories is assessed by two
complementary techniques:
► on-site evaluation by an assessment
team
► proficiency testing

4. Why PT/ ILC ?
First: To ensure that a single operator / analyst
within a laboratory is able to consistently
reproduce the same result on the same sample.
Second: The result produced by this operator/
analyst should reflect the result that would have
come from any other analyst in the laboratory.
Third: Any results from the laboratory as a whole
should reflect the results that are agreed upon by
many other laboratories.

5. ILC-PT
 It is one of the techniques by which the data
produced by a lab/ method/ software/ procedure is
validated.
 It is means of quality control for objectively assessing
the quality control procedures of a lab.
 Objective means of assessing the reliability of data
they are producing.
 It is method to check a lab’s testing / calibration
performance.
 Performance within its own lab and with other labs.
 Provide additional confidence to the lab’s customers.
 It is pre Accreditation activity.

6. ILC /PT in ISO/IEC 17025
 ISO/IEC 17025 (clause 5.9.1) The laboratory shall have
quality control procedures for monitoring the validity of tests
and calibrations undertaken…. This monitoring…may
include…
b) participation in inter-laboratory comparison or proficiency
testing programmes;
 ISO/IEC 17011 (clause 7.15.3) The accreditation body shall
ensure that its accredited laboratories participate in
proficiency testing…
where available and appropriate, and that corrective actions
be carried out when necessary.

7. ISO 17043
 This standard is for accreditation of PT providers
 This standard consists the technical and management
requirements for PT providers
 This standard replaces the earlier guides ISO guide 43-1
and 43-2
 It allows some activities to be outsourced

8. Organization of performance and evaluation
of tests on the same or similar test items by
two or more laboratories in accordance with
predetermined criteria.
Some Definitions
Inter-laboratory comparisons

9. The variation in the results of successive measurements of same
parameter / sample within a lab
Within lab variance
Between Lab variance
The variation in the results of measurement of same
parameter / sample in different labs

10. The normalized value which gives a ‘score’to each result
relative to the other members in the group. So a z score value
close to zero means that the result agrees well from the other
values.
Z score
laboratory that provides reference values on a test item.
Reference laboratory

11. The normalized error (corresponding to z score) and
used in judging the quality of measurement by
calculating the error normalized with respect to the stated
uncertainty
En score

12. Measurement Comparison
Schemes
Interlaboratory Testing
Schemes
Split Sample Testing Schemes
Qualitative Schemes
Known Value Schemes
Partial Process Schemes
Proficiency Testing Schemes

13. Lab
1
Lab
2
Lab
3
Lab
4
Ref
Lab
Same Sample
Measurement Comparison Schemes

14. Circular Model
Lab 5
Lab 4 Lab 3
Lab 2
Reference Lab
Lab 1

15. Hybrid Model
Lab 5
Lab 4 Lab 3
Lab 2
Reference Lab
Lab 1
Lab 6

16. Petal Model
Lab 5
Lab 4 Lab 3
Lab 2
Reference Lab
Lab 1

17. Homogeneous
Sample
• Lab 1
Homogeneous
Sample
• Lab 2
Homogeneous
Sample
• Lab 3
Homogeneous
Sample
• Lab 4
Homogeneous
Sample
• Lab 5
Inter Laboratory Testing Schemes
Homogeneous samples (part of one sample)

18. Sample part
1 to Lab 1
Sample part
2 to Lab 2
One Sample
Split Sample Testing Schemes

19. Qualitative Testing Schemes
Coordinator
Evaluate Lab’s performance Multiple labs may not be involved
Lab
Asked to test specially prepared sample
Special Test Item
Type of Asbestos, Special Pathogen etc.
to evaluate the capabilities of laboratories to characterize
specific entities

20. Known Value Schemes
Sample with known
measurand
Lab 1 Lab 2
Coordinator for evaluation
to evaluate the lab’s capability to test the item and provide
numerical results for comparison

21. Partial Process Schemes
To evaluate the lab’s capability to perform part of the test or
the process.
Data from earlier
testing / measurement
Lab for evaluation /
reporting
Regulatory Body /
Accreditation Body

22. Process of Proficiency Testing Program
The various steps in Proficiency Testing Program are described below:
Sample
Distribution
Lab Testing &
submission of
results
Statistical Analysis
of Results
Generation of PT
Report with statistical
Outliers
Analysis of
their result by
labs and taking
corrective
actions
Activities prior (planning) to this may include
1. Design of Program, marketing, selection and registration of participating labs
2. Selection of sub contractor (if required)
3. Preparation of PT Sample which are homogenous and stable
Planning

23. Basic organization and management
Need
Parameter
Range
Uncertainty
Organise
Ref. Lab
Data
Processor
Coordinator
Selection of
Participants
Execute
Transport
Participants
measure
Data
processing
Ref. Lab
measure
Plan
objectives
Traveling
standard
Schedule
Design
experiment
Analyse & Report
Act
Act on
findings
Analyse
Results
Process
Improvement
Distribute
Data
Analysis
Prepare
Report
Typical structure of PT

24. Calculation & evaluation of performance
• Statistic for quantitative results
- Difference (x - X), where “x” is participant results
X is the assigned value
- Percentage (%) difference (x - X) x 100
X
- Percentile or rank
- Z score
- En number (measurement comparison scheme)
• No calculation for qualitative results

25. If the results are quantitative, z score is calculated and
performance is judged as per following:
z ≤ 2 = satisfactory
2 < z < 3 = questionable
z ≥ 3 = unsatisfactory
For En Score
En ≤ 1 = satisfactory
En > 1 = unsatisfactory
Performance evaluation

26. Calculation of Z-score
Z-score is calculated using the formula
Z = ABS (Xi-X mean)/SD

27. Example-1
Calculate the z-score of lab 5 using the following information for
assay of sample using HPLC for 12 laboratory participants.
Laboratory Name Assay value
Reference lab………………………………………..96%
1……………………………………………………….98%
2……………………………………………………….92%
3……………………………………………………….95%
4………………………………………………………..99%
5……………………………………………………....109%
6………………………………………………………...97%
7…………………………………………………………96%
8………………………………………………………...99%
9…………………………………………………..…….101%
10…………………………………………………..……100%
11…………………………………………………….….102%
12………………………………………………….……99%

28. True value = value of reference laboratory = 96%
Standard deviation of 11 laboratories = 2.86
Laboratory result number 5 = 109%
Z = ABS (laboratory result 5 – reference laboratory
result)/SD
Z = ABS(109%-96%)/2.86
Z= 4.55
Laboratory 5 is not satisfactory

29. Example-2
Calculate the z-score of lab 9 using the following information for
water content of sample using KF for 12 laboratory participants.
Laboratory Name Assay value
Reference lab………………………………………..1.6%
1……………………………………………………….1.5%
2……………………………………………………….1.3%
3……………………………………………………….1.1%
4………………………………………………………..1.2%
5……………………………………………………....2.0%
6…………………………………………………………1.7%
7…………………………………………………………1.3%
8…………………………………………………………1.3%
9…………………………………………………..…….2.5%
10…………………………………………………..……2.1%
11…………………………………………………….….2.0%
12………………………………………………….……1.3%

30. Any Questions/ suggestions ?