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Why validate an analyser?. Its ensures that an analyser gives the correct resultIt improves patient careThe instrument may not perform as well as the manufacturer claims. Don't believe everything that you read. Why validate an analyser?. It improves the chance of good performance in NEQASIt is a CPA requirement.
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1. Chris Gardiner
Department of Haematology
University College London Hospitals Validation of coagulometers in the diagnostic laboratory:New guidelines
3. Don’t believe everything that you read
4. Why validate an analyser? It improves the chance of good performance in NEQAS
It is a CPA requirement
5. CPA definition Validation - confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled
6. CPA Standards Examination procedures, including those for sampling, shall meet the needs and requirements of users.
Examination procedures shall be validated for their intended use prior to introduction, and the methods used and results obtained, recorded.
The laboratory shall determine the uncertainty of results, where relevant and possible.
10. Existing guidelines/protocols Chemistry analysers
CLSI (NCCLS) guidelines (EP-5, EP-12, EP-15)
Well defined stable analytes
Variety of matrices
Haematology analysers
ICSH 1984 (Clin Lab Haematol 6 (1):69-84)
Measure blood cell parameters
11. Haematology
12. Clinical Chemistry
13. Haemostasis
14. First guidelines for coagulometer evaluation
18. Problems Modern coagulometers are complex
Tailored reagent-instrument systems
Reagent specific algorithms
Unstable analytes
Some tests poorly standardised with no ‘gold standard’ e.g., APTT
19. New Guidelines Recommendations for the evaluation of coagulometers Gardiner, Kitchen, Dauer, Kottke-Marchant & Adcock. (2006) Lab Hematol. 12(1):32-8
Protocol for the Evaluation, Validation, and Implementation of Coagulometers.
Clinical and Laboratory Standards Institute (2008) Approved guideline H57-A
20. Levels of evaluation Type of evaluation
National (eg FDA, MHRA etc)
Beta site
Local (Purchasing laboratory)
Availability of independent evaluation data
Type of work performed
Range of samples available
21. Planning Time required
Staff time
Analyser availability
Reagent quantities
Contingency plan
Reagents held in reserve
22. Preliminary information Price: Instrument, reagents, consumables, leasing…
Requirements: Space, power, operating environment…
Full technical specification: Throughput, sample volume, tests per sample, reagent storage…
Closed tube sampling? Effect on dead volume
Interface: Who will perform interfacing with LIS/HIS
23. Preliminary assessment Safety
Mechanical
Electrical – IEC 61010-1
Microbiological – aerosol, splashing, waste disposal
Installation and training
Training course
Operator’s manual
Preliminary assessment of imprecision
26. Performance assessment Comparability (accuracy)
Reproducibility (precision)
Ease of use
Fit for purpose?
29. Precision testing Lyophilised plasma or frozen pooled plasmas
Within run and total imprecision
3 replicates of 2/3 levels on 3 or 5 separate days (CLSI EP-15 H-57)
Compare %CV with manufacturer’s if available
Useful for establishing uncertainty of results for CPA
30. Precision testing
31. Precision testing On-board stability of reagents
Analyse freshly prepared QC over the stated stability period of the reagents
32. Comparability Comparability rather than accuracy
Accuracy implies a ‘true’ value
Not applicable to many tests (eg APTT, PT, APCR)
Differences between antigenic and activity assays
33. Comparability The reference method will normally be that currently in use,
BUT…… big differences can arise when:
Mechanical and optical clot detection methods are compared
There are significant differences between reagents
recombinant human v rabbit brain thromboplastin
large differences in thromboplastin ISI
natural v synthetic phospholipids in APTT reagents
clotting v chromogenic factor/thrombophilia assays
34. Comparability PT/INR
>50 samples from patients receiving warfarin
?20 normal samples
Verify ISI assignment (use a calibration set)
APTT
? 20 samples from patient receiving unfractionated heparin
Lupus anticoagulant samples
Factor deficient samples (FVIII, FIX, FXI etc)
35. Good comparability
38. Heparin APTT therapeutic range
39. Factor assays Calibration curve reproducibility
Linearity
40. Reference ranges Where ever possible local reference ranges should be established for any new method
Fresh or frozen plasmas from at least 20 healthy individuals should be tested
Sex specific ranges may be required (e.g. protein S assays)
41. Reagent carryover Use when a single probe is used for all reagents and samples
Clauss fibrinogen or antithrombin assays are performed on 5 aliquots of normal plasma followed by aPTT
The sequence is repeated 10 times
Carryover is indicated by a progressive shortening of clotting times
42. Interfering substances Local evaluation: manufacturer’s specifications
Full evaluation: Analyse samples with a broad range of interfering substances
Icterus:
Bilirubin up to 1000 ?mol
Lipaemia:
Triglycerides up to 20 mmol
Haemolysis:
Haemoglobin up to 1.0 g/dL
43. Throughput Manufacturers’ throughput data generated using normal samples often using 2 or 3 tests
eg 160 PT/APTT per hour
Real situation
Sick patients
Wide range of tests performed simultaneously
Reflex tests
Can several test methodologies run at once?
44. What can go wrong…… During 2001, a hospital laboratory using a benchtop coagulometer in Pennsylvania reported 2146 tests with correct PT results but with incorrectly calculated INR results over a 7 week period
This led to several major haemorrhages and two fatalities
This was the result of changing INR method without validation
45. Adjusted relative odds of intracranial haemorrhage by INR