Current practices in donation testing and residual risk of Transfusion Transmitted Viruses

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Current practices in donation testing and
residual risk of Transfusion Transmitted Viruses

• Dr.K.Krishnan, Ph.D

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Tests used for TTI
Front-line screening THE TRIANGLE
Anti-HIV

• Rapid tests
• ELISA tests
• Chemiluminescence methods

Anti-HCV
HBsAg
Tests for residual risks

• NAT test methods
  
• Supplemental marker
• tests

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Rapid tests

• Agglutinating tests
• Latex tests
• Color forming tests
• IC tests

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Rapid tests

• Advantages
• Ease of use
• No capital equipment
• Use in Remote areas
• Quick TAT
• Bed-side tests
• Random test

• Disadvantages
• Sensitivity and specificity is a concern
• Limited area of coating
• Limited washing efficiency
• Subjective visual results

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Rapid tests-Performance examples
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ELISA methods

• Advantages
• 96 tests format
• Objective results
• Automatable
• Appreciable sensitivity Specificity
• Narrower detection window

• Disadvantages
• Demands skill sets
• Decade old method
• Detection capability surpassed by newer methods
• Sero-conversion detection panels

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Chemiluminescence methods
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Chemiluminescence methods

• Limitations
• Limited suppliers
• Capital equipment

• Advantages
• Lasting luminescence
• Increased sensitivity
• High precision when automated
• Wider detection limits

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Enhanced Chemiluminescence

• Example of Sero-conversion sensitivity

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TESTS FOR RESIDUAL RISK for TTI

• NAT test methods
  
• Supplemental marker
• tests

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NAT testing

• How is NAT Testing Performed in Blood Screening?
• In most countries NAT testing for blood screening
  is performed on pooled samples (pool size varies
  between 1 to 96 across countries) by one of the
  following methods
• PCR - Polymerase Chain Reaction
• Roche Cobas Ampliscreen
• TMA Transcription Medicated Amplification
• Chiron Geneprobe

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NAT methods

• Advantages
• Direct detection of viruses
• Higher sensitivity than ELISA
• Closure of window period of detection

• Limitations
• High skill sets
• High TAT
• Infra-structure
• Sample processing step yet to be automated
• Room for error
• Cost of single NAT 10X ELISA

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NAT Testing

• Will NAT Testing replace existing Immunoassay
  screening tests in Blood Screening?
• NO,
• Small percentage of Antibody positive donors have
  been tested negative by NAT tests.
• It is possible that an antibody positive and NAT
  Negative donation might transmit infection to the
  recipient.
• Therefore NAT Testing will not replace current
  serology tests in blood screening 1,2
• So far no country has discontinued the serology
  screening for HBsAg, Anti HIV and Anti HCV after
  implementation of NAT screening
• 1http//www.bloodservices.ca/CentreApps/Internet/U
  W_V502_MainEngine.nsf/9749ca80b75a038585256aa20060
  d703/708f54b29790a54585256abe0050069d?OpenDocument
  
• 2.http//72.14.203.104/search?qcache63M5sxAngMoJ
  www.nzblood.co.nz/site_resources/PDF_Documents/dn
  r_nat.pdfwillNATreplaceAntibodyscreeninghle
  nglusctclnkcd5

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Alternatives to NAT
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Alternative to NAT

• Complete closure of window of detection in HIV
  HCV- as good as NAT

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HBsAg aHBc test for complete window closure

• aHBc test still mandatory in U.S. blood banks
• Apollo group / Private segment isnt far !

Complete window closure
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aHBc scores where NAT fails
Why? 6/69 donors who transmitted HBV were shown
to have a-HBc but no HBV DNA. Some HBsAg
anti-HBc were HBV DNA negative
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aHBc testing

• Advantages
• Complements Questionnaire
• Existing platform
• Just another additional test
• Small step for a lab but BIG step in blood
  safety!!
• Limitation
• No confirmatory tests
• Reduces donor pool

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aHBc testing -Suggested algorithm
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anti-HBs- Half Back?
TK Ghosh Birla Kolkata
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How safe is aHBs? A Literature Review.

• Anti-HBs positive subjects are much less
  infectious ( Allain Vox Sang 86, 83-91 2004. 97
  components with low a-HBc positive a-HBs given to
  131 recipients gave no transmission)
• Low levels of viraemia may be less infectious
• Gerlich, Boxall (CDC 2, 178, 1999)- less than
  1000 copies/ml may be less infectious.

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Add Fourth Angle to the Triangle

HIV test

• aHBc test

HCV test
HBsAg test
aHBc to the current menu adds Blood safety
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Its all about double protection! Thank you