Update on HIV Testing

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Update on HIV Testing
A Very Fast
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Message

• There are numbers of tests
• They should be used in combination (strategies)
• Combinations must be consistent

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Laboratory Tests

• diagnosis of infection
• acute, recent, established or late stage disease
• prognostic markers
• monitoring of ARV therapies
• immunological and virological markers
• toxicities
• diagnosis of opportunistic infections
• drug resistance testing

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typical primary HIV-1 infection
symptoms
symptoms
HIV proviral DNA
HIV antibodies
window period
HIV viral load
HIV-1 p24 antigen
0 1 2 3 4 5 6 / 2 4 6 8 10
1 infection
weeks
years
Time following infection
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HIV Assays Methodologies FOR THE DIAGNOSIS
(DETECTION) MANAGEMENT OF HIV
Virus Detection Quantification
RNAmodified Ag Viral Culture, phenotyping
EIASimple, rapid tests Immunoblots Incident
assays
Antibody Antigen Detection
ARV Resistance genotypingARV Sensitivity
CD4
DNA(RNA)
DIAGNOSIS
MANAGEMENT
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Spectrum of anti-HIV testing
early
recent / established
advanced
DNA PCR
RNA PCR
p24 Ag
3rd gen ELISA
1st gen ELISA
Detuned ELISA
1wk 2wk 3wk 2mo 6mo 1yr
2yr 3yr 8yr
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HIV Testing -Direct Detection of Virus

• HIV p24 antigen serology
• - In isolation or Ab/Ag Combo test
• - Diagnosis of primary infection viraemia
• Virus culture / isolation
• Nucleic acid detection - (NAT)
• Clinical uses Proviral DNA vs. plasma
  RNA(viral load)
• resolution of inconclusive serology /
  neonatal
• subtyping
• drug resistance monitoring

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Principle of Immunoassays
ANTI-HUMAN IMMUNOGLOBULIN WITH DETECTOR
SAMPLE ANTIBODY
ANTIGEN
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Available Assays

• EIAs including
• rapid, simple
• particle agglutination,
• dot/blot
• Western blot
• Antigen Ab/Ag
• Incidence assays
• Direct Virus Detection

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Particle Agglutination
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Western Blot

• Expensive 80 - 100
• technically more difficult
• visual interpretation
• lack standardisation
• - performance
• - interpretation
• - indeterminate reactions resolution of ??
• Gold Standard for confirmation

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Antibody testing limitations

• Difficulties in interpretation
• Limitations - window period
• antibodies appear within 3-4 weeks
• Direct detection HIV p24 antigen or DNA/RNA
  (NAT) pre-antibody
• Combo test earlier detection
• Primary infection therapy delayed antibody
  response

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Ag/Ab Combo tests
Ab Ag

• Detection of Ag Ab in a single test
• utility in primary infection pre-seroconversion
  window period
• Incident populations at risk
• Blood bank
• Automated platforms available

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Issues with Combo Assays

• Testing strategies
• False reactivity rates
• Confirmation strategies
• Replacement of other assays (especially in the
  USA)
• Cost
• Legal issues

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Conclusions

• HIV-1/2 Ag/Ab combo assays perform well
• Differences in limit of detection of Ag
• (140 - lt25 pg/mL)
• May shorten window period by 3-5 days
• PHI detection without indication
• Issues associated with introduction
• Strategies and confirmatory algorithms
• ARV therapy effects seroconversion events

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What about simple assays?
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HIV Determine test

• Detect HIV-1 HIV-2
• Cannot differentiate
• Procedural control anti Hu IgG
• Whole blood or serum/plasma
• Widely available
• No additional reagents required
• Room temperature storage
• 15 minutes to result

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BioRad HIV-1/2 Multispot

• Detects HIV-1 and HIV-2
• Will differentiate 1 and 2
• Procedural control anti-Hu IgG
• Serum / plasma only
• Additional reagents (included)
• Requires refrigerated storage
• Immunoconcentration principle
• 15 minutes to result

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WHO Recommended Strategies

• Strategy I Test all samples with one EIA
• Strategy II Strategy I with all reactives
  retested in a more specific test with different
  principle and/or antigen.
• Strategy III Strategy II with reactives tested
  in a third test differing from the first two
  tests.

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WHO Recommended Testing Strategies

• Transfusion safety
• Surveillance
• Diagnosis
• Risk factors
• No risk factors

• Strategy I
• gt10 I
• lt10 II
• Strategy II
• gt10 II
• lt10 III

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Testing Strategies

• AIM To develop the logic used in establishing
  the use of HIV tests (testing strategies)

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Objectives of Testing Strategies

• To achieve the correct diagnosis in the most
  efficient manner
• To maintain consistency in testing
• To know the predictive value of the testing
  process
• To develop baseline data for assessing changes
• To deliver useful results

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Aims in Developing HIV Testing Strategies

• To arrive at the correct sero-diagnosis
• To minimise total testing thus cost
• Minimise samples classed as indeterminate or dual
  reactors
• Detect HIV-1 negative but HIV-2 positive
• Follow likely seroconverters (HIV-1 or -2)

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Screening Assays

• Are used to detect antibody-- specific or
  nonspecific
• Are designed to handle large numbers of samples
  with rapid throughput
• Must be high performance
• Should include a full range of HIV antigens

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Ab Ag AbAg
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AbAg
Ab Ag
Ab Ag
AbAg
Ab Ag
AbAg
Ab Ag
AbAg
AbAg
Ab Ag
Ab Ag
AbAg
Ab Ag
AbAg
AbAg
Ab Ag
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Serological Testing Strategy
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HIV Testing Strategy
HIV1/2 SCREEN
NEG
SCREENING
REACTIVE
HIV-1 WB
POS
NEG
IND
NEG
SUPPLEMENTAL
ADDITIONAL TESTS
POS
IND
POINT OF REPORTING
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Supplemental Assays

• Range of assays that further define sero-status
• High Performance (higher specificity)

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The Use of Screening Assays

• Define samples as negative for a given analyte
• Enable high throughput

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Assay Selection depends on

• laboratory infrastructure
• access to reference laboratory
• desired characteristics of the test
• equipment
• performance time
• shelf life and stability of reagents
• price
• technical skills of personnel
• support (technical, kit supply, etc)

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Predictive Values

• Positive Predictive Values
• The likelihood of a sample identified as a
  reactive by a test being truly POSITIVE for the
  analyte used as the basis of the test.

True Positives
PPV

X 100
True Positives False Reactives
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Predictive Values

• Negative Predictive Values
• The likelihood that a sample identified as a
  non-reactive by a test is truly NEGATIVE for the
  analyte used as the basis of the test.

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Negative Predictive Value Non-reactive test,
prevalence 2
Sensitivity
60 70 80 90 95 98
99

99.17 99.38 99.59 99.79 99.90 99.96 99.98
99.17 99.38 99.59 99.79 99.90 99.96 99.98
99.17 99.38 99.59 99.79 99.90 99.96 99.98

60 70 90
Specificity
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Positive Predictive Value Reactive test,
prevalence 2
Sensitivity
4.95 4.95 6.49 6.49 9.43
9.43 9.43 17.24 17.24 17.24 17.24
17.24 17.24 17.24 29.41 29.41 29.41
29.41 29.41 29.41 29.41 51.02 51.02
51.02 51.02 51.02 51.02 51.02 67.57
67.57 67.57 67.57 67.57 67.57
67.57
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Cross reactivity
3SD
2SD

1SD
Frequency
1
2
3
Cut-off value
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PPV vs Prevalence
Assay 1 Assay 2 Assays 12

(in sequence)
Sensitivity 99.0 99.0
Specificity 99.5 99.9
Prevalence
PPV
PPV
PPV
0.2 2.0 20.0
28.4
66.4
99.75
80.2
80.2
99.97
98.0
99.6
99.99
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Why Follow a Strategy?
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The Importance of Maintaining a Strategy

• Consistency of laboratory records
• Consistency of results
• Clarity of results to doctors
• Maintaining data base to assess performances
• Avoiding common false reactivity
• Avoiding technical errors
• Reducing costs

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WHO Recommended Strategies

• Strategy I Test all samples with one EIA
• Strategy II Strategy I with all reactives
  retested in a more specific test with different
  principle and/or antigen.
• Strategy III Strategy II with reactives tested
  in a third test differing from the first two
  tests.

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WHO Recommended Testing Strategies

• Transfusion safety
• Surveillance
• Diagnosis
• Risk factors
• No risk factors

• Strategy I
• gt10 I
• lt10 II
• Strategy II
• gt10 II
• lt10 III

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WHO Guidelines

• Other possibilities
• strategy for confirmation
• combination of affordable simple assays
• different test principles
• different antigen preparations
• two or three ELISAs or rapid tests
• diagnosis confirmed by second sample
• detection of virus (PCR)
• antigen detection (limited lab.facilities)
• Always use a QC sample

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Cost of HIV Testing

• comparative costs (AUD)
• ELISA (Ab only) - 2 per test
• EIA (Ab/Ag combo) - 3.50
• rapid test - 10-20 per test
• Western blot 80 - 100
• p24 antigen 30
• PCR - qualitative 80 - 100
• PCR - quantitative (viral load) 90 150
• DNA sequencing (resistance) 400 700

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Summary of Testing Strategies
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Message

• There are numbers of tests
• They should be used in combination (strategies)
• Combinations must be consistent