Validation of screening methods 2002657EC

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Validation of screening methods (2002/657/EC)

• N. Van Wouwe

AFSCA-FAVV
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Definition (2002/657/EC)

• Screening method
• used to detect the presence of a substance or
  class of substances at the level of interest.
• have the capability for a high sample throughput
  
• gt are used to sift large numbers of samples for
  potential non-compliant results.

Exemple ELISA, plate test, biosensor, receptor
test,
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Definition (2002/657/EC)

• Minimum criteria to use an analytical method as
  screening method
• must be validated (traceability)
• must have a false compliant rate of lt5 (ß-error)
  at the level of interest

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Performance characteristics for method validation
(screening)
Qualitative method identifies a substance on
basis of its chemical, biological or physical
propriety (binary response /-,
absence/presence) Quantitative method determines
the amount or mass fraction of a substance
(response numerical value of appropriate unit)
determination is mandatory
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Validation of screening test

• Definition of the scope of the method
• Analyte of group of analytes
• Range of concentration
• List of matrices
• Initial validation with the most often used
  matrice in national monitoring program
• Detection capacity (CCß)
• Selectivity/Specificity
• Applicability/ Ruggedness/Stability
• Precision (only for semi-quantitative method)

If possible different sources of blank material,
different technicians, different days on the same
spiked sample
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Validation of screening test

• Targeted test for 1 compound
• validation for this compound
• Targeted test for a family of compounds
• validation for 1 representative molecule of the
  family (antibody)
• Wide range test for more than 50 different
  molecules
• Validation for at least a list of representative
  compounds
• Common pattern of activity on a specific
  bacteria?
• Common way of action (acting target)?
• Published reference data on validation available?
  

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Proposition of the CRL for antimicrobials (in
milk)
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Performance characteristics

• Detection capacity
• Selectivity/Specificity
• Applicability/ Ruggedness/Stability
• Precision (only for semi-quantitative method)

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Detection capability (CCß)

• The smallest content of the substance that may be
  detected, identified and/or quantified in a
  sample with an error probability of ß
• In case of MRPL, CCß lowest concentration at
  which the method is able to detect truly
  contaminated sample with a statistical certainty
  of 1-ß
• In case of MRL, CCß concentration at which the
  method is able to detect the MRL concentrations
  with a statistical certainty of 1-ß

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Detection capability (CCß)

• No permitted limit
• Analyse 20 blank materials gt CCa 3x
  signal/noise
• Analyse 20 blank materials fortified at CCa
• gt CCß CCa 1.64 x SDRW
• Calibration curve procedure (ISO 11843)
• Analyse of blank material fortified at 0 MRLP,
  0.5 MRLP, 1 MRLP, 1.5 MRLP and 2 MRLP
• Plot analytical results (y-axis) vs
  concentration(x-axis)
• CCa y-intercept (blank) 2.33 x SDRW
• CCß CCa 1.64 x SDRW

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Detection capability (CCß)

• No permitted limit
• If no quantitative results
• Analyse fortified blank samples at and above CCa
• (n 20 / concentration level)
• CCß concentration level where only 5 false
  compliant results remain

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Detection capability (CCß)
CCa
CCb
Blank
1.64xSDRW
2.33xSDblank
a1
ß5
Signal orConcentration
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Detection capability (CCß)

• Permitted limit (MRL)
• Analyse 20 blank materials fortified at MRL
• gt CCa MRL 1.64 x SDRW
• Analyse 20 blank materials fortified at CCa
• gt CCß CCa 1.64 x SDRW
• Calibration curve procedure (ISO 11843)
• Analyse of blank materials fortified at 0.5 MRL,
  1 MRL, 1.5 MRL and 2 MRL
• Plot analytical results (y-axis) vs
  concentration(x-axis)
• CCa MRL 1.64 x SDRW
• CCß CCa 1.64 x SDRW

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Detection capability (CCß)
CCa
CCb
MRL
1.64xSDMRL
1.64xSDRW
ß5
a5
Signal orConcentration
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Performance characteristics

• Detection capacity
• Selectivity/Specificity
• Applicability/ Ruggedness/Stability
• Precision (only for semi-quantitative method)

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Selectivity/specificity

• Specificity ability of a method to distinguish
  between analyte being measured and other
  substances
• problem of interference?
• F(measuring technique, class of compounds,
  matrices,)

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Selectivity/specificity

• How to test specificity for qualitative screening
  method?
• Analyse 20 different blank samples and 20
  positive samples (blind study, same or different
  days/technicians)

Specificity 100 NA/N- Other parameters Accurac
y 100 (PANA)/(N- N) Sensitivity 100
PA/N False positive 100 FP/(N- N) False
negative 100 FN/(N- N)
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Selectivity/specificity

• How to test specificity for semi-quantitative
  screening methods?
• Select potentially interfering substances
  (metabolites, derivatives,)
• Analyse relevant blank samples (n 20)
• Analyse fortified blank samples with interfering
  substances at a relevant concentration
• Estimate the effect of the interferences
• False identification?
• Influence in quantification?
• Identification of the target analyte is hindered?
  

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Performance characteristics

• Detection capacity
• Selectivity/Specificity
• Applicability/ Ruggedness/Stability
• Precision (only for semi-quantitative method)

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Applicability

• Scope of the method must be define in term of
• Matrix (solid/liquid matrix, type of tissue)
• Animal species
• To introduce a new matrix
• Analyse at least 10 different blank material
  fortified at level of interest for the new matrix
  (CCß) test of interferences
• If 10 positive results gt method applicable for
  the new matrix
• If 1 negative result gt 10 additional analyses
• If 1 negative resultgt CCß must be recalculated
  for the new matrix

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Ruggedness

• Ruggedness the susceptibility of an analytical
  method to changes in experimental conditions
• sample material
• analytes
• storage condition
• environmental condition
• sample preparation condition

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Ruggedness

• How to test ruggedness? (during development)
• Identify possible factor that could influence the
  results (the analyst, solvents, pH, T, rate of
  heating,)
• Vary each factor slightly
• If one factor is found to influence results of
  the representative molecule, conduct further
  experiments
• gt acceptability limits for this factor
• (in the method protocol)

Recommendation of CRL analyses of 10 blank and
10 spiked samples at the same concentration and
with minor change of factor to detect influence
on results
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Stability

• Test are not necessary if stability data already
  exist (from other lab or from publication)
• To include in the validation report
• Stability test
• the analyte in solution
• the analyte in matrix
• Aliquots of a fresh solution or sample stored
  under different conditions (T and/or storing
  time)

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Performance characteristics

• Detection capacity
• Selectivity/Specificity
• Applicability/ Ruggedness/Stability
• Precision (only for semi-quantitative method)

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Precision (for quantitative screening)

• Precision the closseness of agreement between
  independent test results obtained under
  predetermined conditions
• Expressed in terms of imprecision / standard
  deviation of test results

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Precision (for quantitative screening)

• How to test precision?
• Repeatability test
• within-laboratory reproducibility test(or
  intermediate precision)
• Reproducibility test (between laboratories
  interlaboratory studies)
• determination of RSD () lt Precision criteria

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Precision (for quantitative screening)

• Repeatability
• 3 concentrations
• 1x 1,5x 2x MRPL
• 0,5 1x 1,5x MRL
• 6 replicates/level
• 3 times
• same conditions

• Within-laboratory Reproducibility
• 3 concentrations
• 1x 1,5x 2x MRPL
• 0,5 1x 1,5x MRL
• 6 replicates/level
• 3 times
• different conditions (analyst, env. condition,)

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Precision (for quantitative screening)

• ANOVA treatment of data gt RSDr RSDRW
• Comparison with precision criteria
• Horwitz equation RSDR() 2(1-0.5logC)
• Criteria for repeatability RSDr 1/2 to 2/3
  RSDR
• Criteria for within-lab reproducibility RSDRW
  2/3 to 1 RSDR

!
For concentration lt 100 µg/kg, RSDR becomes too
high!
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Other recommendations

• False negative rate lt5 Analyses of 20 negative
  and 20 positive samples in order to test the
  screening method (see selectivity).
• One QC sample must be added in routine and
  results must be added to the validation file
• Method transfer/Commercial test
• Bibliographical survey to compil the evaluation
  of performance of the test
• Collection of data from supplier on validation
  study
• Experimental plan to test skillness of technician
  to perform the test
• Use of QC sample
• Participation to proficiency test

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Exemple analyse of PCDD/F by CALUX bioassay

• PCDD/F 17 toxic congeners to analyse in various
  matrices (TCDDmost toxic dioxin)
• Results expressed in TEQ (Sum (CCixTEFi)i1-17)
• MRL for each matrix (milk, meat, egg, fish oil,)
  
• MRL expressed in pg TEQ/g fat or ng TEQ/ kg
• Reference method GC-HRMS
• Screening method immunoassay, bioassay,

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Exemple analyse of PCDD/F by CALUX bioassay
CALUX bioassay genetically modified cell-based
bioassay (luciferase) Amount of light produced is
proportional to the toxicity (TEQ) of extracts
All substances fixing the Ah receptor
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Analyse of PCDD/F by CALUX bioassay

• Advantage
• Rapid
• Cheaper than GC-HRMS
• Time for analyses
• Disadvantage
• Various compounds can fix the Ah receptor (PAH,
  PCB, PHDD/F,)
• specificity!!!!

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Analyse of PCDD/F by CALUX bioassay protocol
Extraction of fat
Clean-up on silica acid carbon columns
Fraction with PCBs
Fraction with PCDD/F
Fraction with interfering compounds
Evaporation
Reading plate
Dosing plate
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Analyse of PCDD/F by CALUX bioassay validation

• Selectivity/specificity
• Ruggedness/Stability
• Precision
• Detection capability

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Analyse of PCDD/F by CALUX bioassay selectivity

• Possible interfering compounds?
• PAH mostly in environmental sample
• PCB fractionation during clean-up
• Other compounds? (PHDD/F) dependant of the
  matrix? (matrix effect?)
• Results of the selectivity test
• No interferences for feedstuff, milk, egg, fat
• Interferences for fish oil
• CALUX results 2 x GC-HRMS results

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Analyse of PCDD/F by CALUX bioassay selectivity

• Matrix effect for fish oil

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Analyse of PCDD/F by CALUX bioassay ruggedness

• What are the critical point in the protocol?
• Carbon column (interferences)
• Solvent (interferences)
• Curve (results)
• Evaporation time (recovery)
• Age of CALUX cell line (RSD)

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Analyse of PCDD/F by CALUX bioassay ruggedness

• Carbon column amount of carbon used

(Rdt PCDD/F 60)
(Rdt PCDD/F 80)
DX fraction
PCB fraction
Not collected fraction
(Rdt PCDD/F 80)
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Analyse of PCDD/F by CALUX bioassay ruggedness

• Evaporation time

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Analyse of PCDD/F by CALUX bioassay ruggedness

• Solvent tested before use on a TCDD solution
  (antagonist/agonist effect)
• Curve tested with an independant TCDD solution
• Age of CALUX cells new cell every 2 months

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Analyse of PCDD/F by CALUX bioassay precision

• Validation protocol

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Analyse of PCDD/F by CALUX bioassay precision

• ANOVA results for the TEQ determination of PCDD/F
  in feedstuff by CALUX bioassay
• At MRL (0.75ng TEQ/kg) XMRL 0.751 ng TEQ/kg
• Sr 0.063 gt RSDr 8.4
• SRW0.073 gtRSDRW 9.7
• At MRL/2 (0.376ng TEQ/kg) XMRL/2 0.464 ng
  TEQ/kg
• Sr 0.051 gt RSDr 11
• SRW0.051 gtRSDRW 11
• At 2MRL (1.5ng TEQ/kg) X2MRL 1.571 ng TEQ/kg
• Sr 0.107 gt RSDr 6.8
• SRW0.115 gtRSDRW 7.3

RSD lt 30 (2002/70/EC)
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Analyse of PCDD/F by CALUX bioassay detection
capacity

• CCß for the TEQ determination of PCDD/F in
  feedstuff by CALUX bioassay
• CCa MRL 1.64 x SRW
• CCa 0.75 1.64 x 0.073 0.87 ng TEQ/kg
• CCß CCa 2.33 x SRW
• CCß 0.87 2.33 x 0.073 1.04 ng TEQ/kg

2002/70/EC false negative rate lt 1 !
gt At a concentration of 1.04ng TEQ/kg, we are
sure that the sample is a positive sample with
99 certainty
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Analyse of PCDD/F by CALUX bioassay confirmatory
range
?
NON COMPLIANT
COMPLIANT
SUSPICIOUS
MRL
CCa
CCb
CC
-2.33sMRL
1.64sMRL
2.33ssample
Signal orConcentration
1
a5
ß5
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Analyse of PCDD/F by CALUX bioassay confirmatory
range

• Lower limit of the confirmatory range for the TEQ
  determination of PCDD/F in feedstuff by CALUX
  bioassay
• CC MRL-2.33 x SDRW
• CC 0.75- 2.33 x 0.073 0.58 ng TEQ/kg
• Conclusion
• Sample lower than 0.58 ng TEQ/kg are negative
  with 99 certainty (false negative rate lt 1)
• Sample above 0.58 ng TEQ/kg must be confirmed by
  GC-HRMS