1. Observations from 20 years of PT in South Africa
Dr Jim McCulloch
Thistle QA
Johannesburg

2. Who am I? Worked in labs from 1965
Experienced and qualified in Microbiology, Chemistry, Statistics and Clinical Chemistry
Msc Medicine, PhD in Clinical Chemistry
Setup Thistle QA in 1990

3. What is Thistle QA all about?
Started with 1 EQA (PT) in 1990 and with 1 employee, me!
Now...
23 PTs, 12 staff members
2500 labs directly enrolled
Data base has results from 60 countries
Data base number over 6000

4. Why would you want PT anyway?
PICK THE CORRECT ANSWER
ISO says we need it
SANAS will look for it
It helps achieve a quality result

5. Aims of PT
To determine the performance of individual labs for specific tests
To monitor the continuing performance of labs
An essential component of a good quality system

6. PT Design Reference values or consensus Defined methods?
Outlier detection and removal
Statistics to use, robust or not?
Size of data base
Report issues
Customer complaints

7. Outliers Wild results, bummers, etc Chauvenet’s Criterion Grubb’s Test
Robust statistics using
ISO 13528: 2005, e.g.
iteration

8. Complaint No 1 from 1990
(We) will not be participating in cycle three of what you euphemistically call your quality control scheme.
Quaint statistical manipulation and unacceptable transcription errors render your scheme more than a little suspect.
Please note that we do not require reports. I would sooner the paper be saved for a more useful function than cluttering up my waste paper basket.

9. Bolt on extras Support Teaching material Seminars Extra samples
Custom designed reports

10. And reports are stats
They are mere sets of figures, albeit with useful information
They give you warnings, not facts
You can be “out of control” and not have a non-conformance
Things are not always what they seem

11. Statistical cliché… Myth: Truth: Mark Twain said:
Lies, damned lies and statistics
Truth:
Statistics don’t lie – it’s people who lie!

12. An example of wrong conclusion...
4/15/2017
Thistle QA

13. Don’t accept the surface

14. Get behind the stats
4/15/2017
Thistle QA

15. Why can you be okay and yet outside 2 SDs (z score >2)?

16. A control chart

17. What target value to use?
By calculation from formulation
CRM RM
Consensus from reference labs
Consensus from participating labs

18. The current reports
4/15/2017
Thistle QA

19. A Review of Chemistry PT
Analytes used
Sodium, measure of osmotic equilibrium
Glucose, likelihood of diabetes
Bilirubin, an assessment of liver function

20. Fitness for purpose – Acceptable Range
Review of Chemistry PT
Fitness for purpose – Acceptable Range
Sodium 3%
Glucose 7.4%
Bilirubin 20.0%

21. Review of Chemistry PT Methodology
Each lab’s results for an entire 6-month cycle
Reduced to one single figure, CV, basically, SD as a percentage of the mean / average result
Reviewed for changes per lab, and overall number of labs within the fitness-for-purpose percentage

22. Review of Chemistry PT Findings Sodium 99.9% within f-f-p range
Glucose 99.3% within f-f-p
Bilirubin 99.1% within f-f-p
General
IF first cycle out, next one always in f-f-p
UNLESS instrument changes

23. Review of Immunoassay PT
TSH, thyroid function test, assessment of thyroid stimulation
T4, thyroid function output test
PSA, prostate specific antigen

24. Review of IA (hormone testing) PT
FFP
TSH, 20%
T4, 15%
PSA, 25%
Methodology
As for Chemistry

25. Review of IA PT TSH, 94.9% within f-f-p T4, 89.9% within f-f-p
PSA, 95% within f-f-p

26. We all see things differently
4/15/2017
Thistle QA

27. The real thing

28. Conclusions PT an essential tool Needs education, interpretation
Can assist in complying with quality standard
Detects changes, e.g. Instrument
Cannot lead to CQI, rather compliance with
f-f-p