HIV Testing Technologies

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HIV Testing Technologies

• Austin Demby PhD, MPH
• Director, CDC-Malawi

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p-24
Antigens Lysate Recombinant Peptide
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Host Response - Evolution of Antibodies
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Spectrum of HIV Tests

• HIV diagnosis (Antibody/Antigen testing)
• Enzyme Immunoassays (EIAs)
• Western blot (WB)
• Rapid tests
• Early diagnosis in infants
• P24
• RNA, DNA PCR
• Initiation of ART
• CD4
• Monitoring of ART
• CD4
• Viral Load

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Enzyme ImmunoAssays (EIAs)
After several incubation and wash steps, a color
reaction occurs if HIV antibody is present
An automated reader gives a measurement of
optical density (presence of color) for each well
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Western Blot / Line Immunoassays

• Used as supplemental test for confirmation (only
  difficult cases)
• Detects antibodies to specific HIV antigens on
  cellulose strip
• Issues
• Multiple standards for performance and
  interpretation
• Expensive
• Limited commercial availability

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HIV Testing Occurs in a Variety of Settings
Prevent HIV Infections
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HIV Rapid Tests

• Qualitative assay to detect HIV antibodies
• Most detect HIV 1 and HIV 2
• As reliable as EIAs
• Serum, Plasma, Whole blood, Oral fluids
• Issues
• Small volumes
• Validation of use
• Appropriate training

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Three Formats of HIV Rapid Tests

• Immunoconcentration (flow-through device)
• Immunochromatography (lateral flow)
• Particle agglutination

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How Immunoconcentration Works

• HIV antibody links to bound HIV peptide antigens
  forming the color spot

Internal Control
HIV-1 peptide
HIV-2 peptide
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Immunoconcentration

• Flow-Through Devices
• Multi-Spot
• Genie II

Top view
Side view
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Reading Results Genie II
Non-reactive
Reactive
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How Immunochromatography Works
Add Sample
Control line
Test Line
Conjugate
IgG Antibodies HIV antibodies
Colloidal gold conjugated to HIV antigen
Anti-IgG/gold antibodies
HIV antigen
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Immunochromatography

• Lateral Flow Devices
• Determine
• Hema-Strip
• OraQuick
• Unigold

Control
HIV Antigen
Sample pad
Specimen Flow
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Reading Results Determine
Non- Reactive
Reactive
Sample Pad
Control line
Test line
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How Particle Agglutination Works
Anti-HIV antibodies bind to the antigen-coated
latex particles.
Antigen
Antibody
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Tests Based On Agglutination

• Agglutination devices
• Capillus
• Serodia

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Reading Results Capillus
Non-reactive
Weak Reactive
Strong Reactive
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There Are Only Three Possible Outcomes for
Single HIV Antibody Tests

• Reactive
• Test band/spot
• Control band/spot
• Non-reactive
• Control band/spot only
• Invalid
• No control band/spot present
• Test has failed. Repeat with new device.

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Choice of Appropriate HIV Rapid Tests

• Testing algorithm
• - test performance characteristics and
  manufacturers characteristics
• Antigen content and source
• - (gp-41, gp-120, gp-160) (p-24) (HIV2 gp-36)
• Test format
• - Flow through, lateral flow, agglutination
• Parallel or Serial testing issues

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Choice of Appropriate HIV Rapid Tests (2)

• WHO list of evaluated HIV rapid tests
• USG (through USAID) list of waived tests
• WHO/CDC Guidelines for test kit
• evaluation in developing countries
• Final test selection should be based on careful
  consideration of all the issues presented

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Challenges to Early Infant Diagnosis

• P-24 assay
• EIA detects p24 antigen before antibody can be
  detected
• Detected 2 to 3 weeks after HIV infection
• Detected about 6 days before antibody tests
  become reactive
• Commercially available assays still a long way
  away
• DNA/RNA PCR assays
• Centralized testing using Dried Blood Spot
  technology
• Expensive and technically challenging
• 1 week turn around

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Key Concluding Messages (1)

• Testing is a critical element of expanding CT
  services. It should be integral to planning and
  not an after-thought
• HIV rapid tests when carefully selected and used
  in combination are as reliable as EIA-WB for
  routine services
• All tests/testing require attention to training,
  supervision, and monitoring at points of service.
• As testing expands and decentralizes, training,
  supervision, and monitoring becomes even more
  important.

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Key Concluding Messages (2)

• Simple ways of providing early infant diagnosis
  (infants lt 18 months) still remains a significant
  challenge and an impediment to CT program
  expansion
• Major investment and a call to action from
  service providers and activists is long overdue
  for arguably one of the most vulnerable of mankind