update from the ifcc working group on commutability · 12/1/2015 · meeting, paris, 1 december...
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Presented at the JCTLM Members and Stakeholders Meeting, Paris, 1 December 2015
Update from the IFCC Working Group on Commutability
Greg Miller, PhD
Virginia Commonwealth University Richmond, Virginia, USA
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Outline
Why commutability matters
What is commutability
How is commutability assessed
What improvements are coming for commutability assessment
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Primary Reference Material
(pure substance) Reference Measurement
Procedure(e.g. Gravimetry)
Manufacturer’sProduct
Calibrator
MedicalLaboratoryProcedure
Manufacturer’sInternal
Procedures
SecondaryReference Material(matrix)
Reference Measurement
Procedure (e.g. IDMS)
PureSubstanceCalibrator
Patient’s Sample
Patient’sResult
Procedures for identity and
mass balance
TRAC
EABI
LITY
Key step for commutability
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Primary Reference Material
(pure substance) Reference Measurement
Procedure(e.g. Gravimetry)
Manufacturer’sProduct
Calibrator
MedicalLaboratoryProcedure
Manufacturer’sInternal
Procedures
SecondaryReference Material(matrix)
Reference Measurement
Procedure (e.g. IDMS)
PureSubstanceCalibrator
Patient’s Sample
Patient’sResult
Procedures for identity and
mass balance
Key step for commutability ILIT
Y TR
ACEA
B
A non-commutable calibrator breaks the traceability chain
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Primary Reference Material
(pure substance) Reference Measurement
Procedure(e.g. Gravimetry)
Manufacturer’sProduct
Calibrator
MedicalLaboratoryProcedure
Manufacturer’sInternal
Procedures
SecondaryReference Material(matrix)
Reference Measurement
Procedure (e.g. IDMS)
PureSubstanceCalibrator
Patient’s Sample
Patient’sResult
Procedures for identity and
mass balance
Key step for commutability ILIT
Y
TRAC
EAB
Even though manufacturers show traceability, the process fails to provide equivalent results for patient samples among different measurement procedures
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Secondary Reference Material
(calibrator)
Procedure n Procedure 3
Procedure 2 Procedure 1
Patient Sample
Must be commutable with patient samples for all measurement procedures with which it will be used
Equivalent Results
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Use of a non-commutable material for calibration traceability will cause:
Incorrect value assignment for a medical laboratory measurement procedure calibrator
Incorrect results for patient samples
Miller, Myers, Rej. Why commutability matters. Clin Chem 2006; 52: 553-4.
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Commutability (Commutable)
Property of a reference material demonstrated by the closeness of agreement
• between the relation among results for a reference material obtained from two measurement procedures
• and the relation among results for clinical samples from the same two measurement procedures
(Rephrased from VIM 3: 2008)
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Clinical Samples
Commutable: same relationship for clinical samples and reference materials
Reference Materials
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Clinical Samples Reference Materials
Non-commutable: different relationship for clinical samples and reference materials
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Calibration with non-commutable materials
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Clinical Samples RM as Calibrator
causes patient sample results to be different
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Correction is possible
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Clinical Samples RM as Calibrator
if the bias is known, a correction is
possible
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Method specific correction can
achieve harmonization
Correction is possible
Clinical Samples RM as Calibrator
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Must require commutability validation for reference materials intended for use with:
• Manufacturer’s internal procedures
• Routine clinical laboratory procedures
Guidelines are available from CLSI:
EP30-A Characterization and qualification of commutable reference materials for laboratory medicine (2010 as C53-A)
EP14-A3 Evaluation of commutability of processed samples (2014)
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1. Representative clinical samples
2. Candidate reference material(s)
3. Measure clinical samples and reference material(s) with all measurement procedures for a measurand
Validating commutability
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4. Determine the relationships between the measurement procedures for the clinical samples
5. Determine if the relationships for a RM are close enough to those for the clinical samples for the intended use of the RM
Validating commutability
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Adapted from CLSI EP30-A (used with permission)
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95% Prediction Interval
Deming Regression Line
Native Clinical Samples Reference Materials
Non-commutable
Commutable
Commutable
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Adapted from CLSI EP30-A (used with permission)
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Measurement Procedure 1 Result
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95% Prediction Interval
Deming Regression Line
Native Clinical Samples Reference Materials
Criteria for commutability near decision thresholds not
resolved
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Modified from CLSI EP30-A (used with permission)
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95% Prediction Interval
Deming Regression Line
Native Clinical Samples Reference Materials
More scatter in the relationship should not make the RMs
commutable
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IFCC Working Group on Commutability (established March 2013)
• Operating procedures for the formal assessment of commutability
• Criteria for commutability taking into account the intended use of a reference material and the medical use of measurement procedure results
• Standard terminology to describe commutability characteristics
• Information to be provided regarding commutability
• Education of manufacturers, laboratories, end users
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Assessment of commutability
Evaluating a property of a reference material
NOT evaluating the performance of the measurement procedures
Assessment of closeness of agreement is influenced by the performance of the measurement procedures
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Qualification of measurement procedures
Measurement procedure improvement may be a prerequisite for inclusion in a commutability assessment
1. Adequate specificity for the measurand
o Good correlation between measurement procedures for clinical samples
o Small error component from sample specific effects
2. Adequate precision
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Qualification of clinical samples
1. Should not contain unusual interfering substances or analyte forms that will influence the measurement procedures
2. Must cover the concentrations of the RM(s)
3. Individual samples are preferred
4. Pooled samples may be needed to meet volume requirements – pooling must be validated
5. Preparation and storage conditions must be validated
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Criteria for commutability
1. Criteria based on statistical distribution of results for patient samples are difficult to apply consistently
o Criteria change among measurement procedures with different performance characteristics
o Criteria may not relate to intended use
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Criteria for commutability
2. Fixed criteria based on the medical requirements for using patient results are preferred
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How to establish criteria based on medical use requirements
CCLM 2015;53(6) Special Issue: 1st EFLM Strategic Conference “Defining analytical performance goals − 15 years after the Stockholm Conference”
Fraction of the uncertainty required for a RM’s use in a calibration traceability hierarchy
Fraction of the uncertainty required for assessment using EQA
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Criteria for commutability
3. A RM should be suitable for use by a large fraction of measurement procedures
o A large fraction is challenging to specify
Number of measurement procedures
Number of clinical results reported
o Labelling should declare for which measurement procedures a RM was evaluated and for which its commutability is or is not suitable for use
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Statistical models
1. Assess closeness of agreement for the difference in bias between two measurement procedures for RM compared to clinical samples
2. Assess harmonization effectiveness of a RM used for calibration traceability by a group of measurement procedures
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Closeness of agreement model
Assess closeness of agreement vs. a fit-for-purpose fixed criterion
NOT assessing the equivalence of the relationship
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Closeness of agreement model
1. Estimate the bias between 2 measurement procedures for the patient samples and for the reference material(s)
2. Estimate the precision error components including sample specific effects
3. Calculate the difference in bias for reference material(s) vs. patient samples
4. Estimate the uncertainty of the difference in bias
5. Commutable if the difference in bias plus uncertainty are within a criterion that is suitable for the intended use of the reference material
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Difference in bias vs. fixed criteria
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Difference in bias vs. fixed criteria
Commutable: bias plus uncertainty is
within criteria
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Difference in bias vs. fixed criteria
Non-commutable: bias plus uncertainty
exceeds criteria
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Difference in bias vs. fixed criteria
Indeterminate: bias plus uncertainty overlaps criteria
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Harmonization effectiveness model
1. Estimate the inter-measurement procedure CV for each clinical sample’s results
2. Calculate an overall pooled inter-measurement procedure CV and its uncertainty for all clinical samples
3. Compare the pooled CV plus uncertainty to a fixed fit-for-purpose criterion
4. Use the RM for calibration traceability and repeat steps 1-2-3
o Can be a mathematical recalibration
o Or a physical recalibration
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Inter-Measurement Procedure CV (%)
20%
10%
5%
0%
Criterion
Harmonization effectiveness
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Inter-Measurement Procedure CV (%)
20%
10%
5%
0%
Criterion
Raw Data
Harmonization effectiveness
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Inter-Measurement Procedure CV (%)
20%
10%
5%
0%
Criterion
Raw Data
Not Commutable RM 1 as calibrator
Harmonization effectiveness
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Inter-Measurement Procedure CV (%)
20%
10%
5%
0%
Criterion
Raw Data
Not Commutable RM 1 as calibrator
RM 2 as calibrator Indeterminate
Harmonization effectiveness
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Inter-Measurement Procedure CV (%)
20%
10%
5%
0%
Criterion
Raw Data
Not Commutable RM 1 as calibrator
RM 3 as calibrator
RM 2 as calibrator Indeterminate
Commutable
Harmonization effectiveness
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Commutability decision applies at a point in time
1. Applies to the RM and measurement procedures included in the commutability assessment
2. Influences such as new reagent lot or other changes in measurement conditions may alter commutability
3. The commutability of a RM may change on storage
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Assumptions
The commutability of a RM does not change over time
o RM is stable on storage
o Insignificant influence of changes in measurement conditions such as new reagent lots or maintenance items over time
The difference in bias between RM and clinical samples is the same over time irrespective of changes in measurement conditions or RM storage
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Correction for non-commutability
A correction for non-commutability can be applied to the quantity value of a RM to make it useful for a measurement procedure for which it otherwise would not be suitable for use
o A correction for non-commutability can improve harmonization of patient results
o and is better than calibration with a non-commutable RM
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Correction for non-commutability
Closeness of agreement model allows the magnitude of non-commutability (difference in bias) to be quantitated
Harmonization effectiveness model allows a correction to be applied to a RM value and the subsequent improvement in inter-measurement procedure CV to be assessed
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Correction for non-commutability
3. Requires the correction to be consistent over time and not influenced by changes in measurement conditions or changes in the RM
The same assumptions are made for a commutable RM
The magnitude of the difference in bias that caused a non-commutability decision is larger
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Correction for non-commutability
Can we have confidence in consistent performance when the influence quantities that caused non-commutability are unknown – is the confidence related to the magnitude of a difference in bias
Key influence quantities
Clinical samples – molecular forms, interferences
RM formulation – source of matrix, supplements, artifacts
Reagent formulation – reactive components, impurities
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Correction for non-commutability
4. Requires the uncertainty of a correction to be small enough for the intended use of a RM
5. The correction is determined by the user of a RM based on additional experimental data beyond what was used for the commutability assessment
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Commutability for a new lot of RM
New lots of RM may not require a new full commutability assessment if prepared to the same specifications
o A challenging task when using biological materials
o The specifications must be complete
A validation scheme is being investigated
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Validation approach
Measure commutable RM and new RM in the same run by measurement procedures in the original commutability assessment
Calculate the ratio of results
Ratios that are the same mean the new and old lots have the same commutability
Should a small number of clinical samples also be included
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Commutability: who is responsible
Reference material producer Cannot know all procedures in use
Should make a material likely to be commutable
Should validate for commonly used procedures
Measurement procedure producer Must confirm commutability for an intended use
Responsible for new procedures introduced
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Questions / Comments