QCMD State of the art molecular external quality assessment for sexually transmitted pathogens

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QCMDState of the art molecular external quality
assessment for sexually transmitted pathogens
QUALITY CONTROL for MOLECULAR DIAGNOSTICS
William G MacKay PhD Neutral Office
Coordinator QCMD Block 4.1, Kelvin Campus West
of Scotland Science Park Glasgow G20 0SP
williammackay_at_qcmd.org
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More work for laboratories means a greater need
for EQA support
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Number of EQA participants increasing
HIV
HSV
C. trachomatis
N. gonorrhoeae
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Cumulative total datasets in HIV EQA since 2002
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What can we say about the performance of NATs for
the diagnosis of STDs?
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The issues

• False positives
• Assay contamination
• Assay specificity
• False negatives
• Assay sensitivity
• Strain variation
• Quantitative accuracy
• Assay/operator variation

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False positives
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False positive results

• False positives caused by
• Assay contamination
• Assay specificity issues
• Assay contamination an important concern in all
  assays (including molecular diagnostics)
• Assays may pick up on closely-related species

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False positive results late 20th Cent.
Early-mid 1990s
Late 1990s
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False positive results early 21st Cent.
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False positives in the QCMD STD EQA programmes
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Assay specificity

• Results of the QCMD EQA programmes for N.
  gonorrhoeae show repeatable evidence of false
  positives on closely related Neisseria spp.

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Assay specificity

• A proportion of conventional commercial PCR
  assays report false positives on some
  closely-related Neisseria spp.
• Issues with closely related species
  (N. lactamica) and assays that target highly
  conserved regions of the Neisseria spp. genome
• Confirmatory testing required on all
  N. gonorrhoeae positive test results

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Assay specificity

• Results from the 2007 QCMD EQA programme for N.
  gonorrhoeae

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False negatives
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False negative results

• False negatives caused by
• Sensitivity issues
• Strain variation
• Assays vary considerably in reported limits of
  detection
• Some strains can cause problems with
  currently-used NATs

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Assay sensitivity

• Reported lower limit of detection in the 2008 EQA
  for HIV RNA

90
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Assay sensitivity

• Results from the 2008 QCMD EQA programme for HIV
  RNA

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Strain variation

• Results from the 2007 QCMD EQA programme for HIV

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Strain variation
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Strain variation

• The Swedish strain of C. trachomatis emerged in
  2006
• Missing 377 base pairs of the cryptic plasmid
• Several counties in Sweden reported an apparent
  decrease in reported cases
• Variant scarcely reported outside of Sweden

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Strain variation

• Results of the QCMD EQA programmes for C.
  trachomatis show evidence of false negatives on a
  specific variant of the pathogen

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Quantitative accuracy/variation
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Quantitative accuracy/variation

• There is no such thing as a true gold standard
  in molecular diagnostics
• A number of initiatives on the provision of
  reference materials and WHO supporting use of
  standardised international units (e.g for HIV)
• Still there can be a large variation on reported
  quantitative results

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Quantitative variation

• Results of the 2008 HSV EQA

HSV 1
HSV 2
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Technology variation

• Results of the 2008 HSV EQA (HSV 2)

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How to improve quality in molecular diagnostics?
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How to improve quality in molecular diagnostics

• Clear understanding of clinical requirements
• Careful planning and design
• Rigorous optimisation and continuous
  re-evaluation
• Quality control

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QCMD state of the art EQA panels

• Help labs to determine their own performance
• Designed by experts
• Consist of 8 - 12 samples
• Include different serotypes / genotypes at
  various concentrations
• Reporting time 4 - 6 week
• Accompanied by questionnaire on technical details

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QCMD panels designed by experts

• Extended panels dilution series, duplicates,
  negative samples, specificity samples

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QCMD detailed reporting and feedback

• Detailed summary reports
• Includes comprehensive reporting and scoring
  systems for qualitative and quantitative data
• Accompanied by individualised reports
• Access to experts

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Summary the issues

• False positives
• Assay contamination
• Assay specificity
• False negatives
• Assay sensitivity
• Strain variation
• Quantitative accuracy
• Assay/operator variation

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QCMDState of the art molecular external quality
assessment for sexually transmitted pathogens
QUALITY CONTROL for MOLECULAR DIAGNOSTICS
William G MacKay PhD Neutral Office
Coordinator QCMD Block 4.1, Kelvin Campus West
of Scotland Science Park Glasgow G20 0SP
williammackay_at_qcmd.org