Unit 5: Choosing an HIV Test

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Unit 5 Choosing an HIV Test
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Warm Up Questions Instructions

• Take five minutes now to try the Unit 5 warm up
  questions in your manual.
• Please do not compare answers with other
  participants.
• Your answers will not be collected or graded.
• We will review your answers at the end of the
  unit.

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What You Will Learn

• By the end of this unit you should be able to
• describe the advantages and disadvantages of
  different HIV testing options
• describe how to choose a strategy for HIV testing
  

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What You Will Learn, Cont.

• By the end of this unit you should be able to
• understand the difference between sensitivity and
  specificity of a laboratory test
• identify the phases of the testing process, and
  what quality control and quality assurance
  programmes should be implemented in each phase

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Selecting an HIV Antibody Test

• Currently a wide range of different HIV antibody
  tests are available, including
• Conventional enzyme immunoassay (EIA)
• Rapid tests

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Table 5.1. Comparing EIAs and HIV rapid tests
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Selecting an HIV Testing Algorithm

• UNAIDS and WHO recommend three criteria for
  choosing and HIV testing algorythm or strategy
• objective of the test (surveillance, blood
  screening, etc)
• sensitivity and specificity of the test(s) being
  used
• HIV prevalence in the population being tested

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Table 5.2. Selection of HIV Testing Algorithms
for Surveillance
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Sensitivity and Specificity

• Sensitivity refers to the ability of a test to
  detect all persons with a disease
• Specificity refers to a tests ability to detect
  all persons who do not have a disease

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Positive and Negative Predictive Value

• Positive predictive value proportion of positive
  tests that identify people who truly have a
  disease
• The more frequent a disease is in a population,
  the higher the positive predictive value of a
  test is.
• Negative predictive value proportion of negative
  tests that identify people who truly do not have
  a disease

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Table 5.3. Guide for Calculating Sensitivity and
Specificity
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Testing Strategy 1

• Requires one test
• For use in diagnostic testing in populations with
  an HIV prevalence gt30 among persons with
  clinical signs or symptoms of HIV infection
• For use in blood screening, for all populations
  regardless of the estimated prevalence in
  population being tested

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Testing Strategy 1, Cont.

• For use in surveillance testing in populations
  with an HIV prevalence gt10 (for example,
  unlinked anonymous testing for surveillance among
  pregnant women at ANCs)
• No results are provided

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Testing Strategy 2

• Requires up to two tests
• For use in diagnostic testing in populations with
  an HIV prevalence 30 among persons with
  clinical signs or symptoms of HIV infection or
  gt10 among persons with no such signs or symptoms
  

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Testing Strategy 2, Cont.

• For use in surveillance testing in populations
  with an HIV prevalence 10 (for example,
  unlinked anonymous testing for surveillance among
  pregnant women at ANCs or patients at STI
  clinics)
• No results are provided

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Figures 5.1 and 5.2. Strategies for HIV Testing
Strategy 1 Strategy 2
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Selection of HIV Testing Technologies

• Decide which testing format to use
• an enzyme linked immunoassay (EIA),
• rapid EIA testing, or
• a combination of the two
• Conditions to consider include
• laboratory infrastructure
• availability of skilled laboratory personnel
• existence of quality assurance and control
  measures

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Laboratory Testing

• The laboratory tests now in use have
  sensitivities and specificities of 99 or more.
• In sub-Saharan Africa, HIV tests performed must
  be able to detect the presence of antibodies to
  both HIV-1 and HIV-2.
• An additional test is required to distinguish
  between HIV-1 and HIV-2.

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Quality Control

• Quality control process for running the
  specimens (such as using positive and negative
  controls), done in the lab facility itself
• To verify test device is accurate, external
  positive and negative controls must be tested.
• The test kit manufacturer or a reference
  laboratory can provide these controls.
• Positive controls specimens known to be positive
• Negative controls are specimens known to be
  negative

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Quality Assurance

• Quality assurance process for comparing results
  obtained for a specific test with other tests
  done on the same specimen, done by the lab itself
  or by outside reference laboratory
• Laboratories should monitor and assess quality
  during three phases of the testing process
• pre-analytical activities that occur before a
  specimen is tested
• analytical the actual testing of the specimen
• post-analytical activities done after a specimen
  has been tested

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Table 5.5. Quality Assurance Pre-Analytical
Phase

• Training
• Laboratory safety
• Number of trained personnel available and capable
  of performing HIV testing
• Specimen collection, labelling and transport
  conditions
• Deciding on handling of specimens before testing

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Table 5.5. Quality Assurance Pre-Analytical
Phase, Cont.

• Deciding on the sources and types of specimens to
  be tested
• Deciding on the number of specimens tested
• Selection of test kits
• Expiration dates of test kits. Kits need to be
  used before expiration dates. Older kits should
  be used before newer kits.
• HIV test kit reagents. Reagents must be stored at
  the appropriate temperature as specified by the
  manufacturer.

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Table 5.5. Quality AssuranceAnalytical Phase

• Specimen processing and storage
• Written procedure manual
• Reagent preparation
• Testing performance
• Performance and maintenance of equipment
• Correct use of reagents
• Inclusion of internal quality controls in test
  kits
• Quality control monitoring procedure

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Table 5.5. Quality Assurance Post-Analytical
Phase

• Interpreting results
• Transcribing results, such as recording results
  on the correct identifier code
• Entering data into the tracking system (computer
  or hard copy)
• Maintaining records
• Reviewing quality control

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Internal Quality Assurance

• Internal quality assurance is meant to allow
  laboratory technicians to check their performance
  for themselves
• An aliquot of every twentieth negative and every
  fifth positive specimen is put aside.
• Once there are sufficient stored aliquots, stored
  specimens are tested a second time.
• Lab technicians compare initial results and
  results of re-testing to monitor reliability of
  techniques.

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External Quality Assurance

• Countries should require that all laboratories at
  all levels participate in an external quality
  assurance programme.
• This may be instituted either by a national or
  international reference laboratory.
• Proficiency testing should be done 1-2 times a
  year.

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External Quality Assurance, Cont.

• In areas with limited infrastructure, labs can
  prepare a dried blood spot on filter paper to be
  tested at the national reference laboratory.
• External quality assurance for national reference
  laboratory should be provided by an independent
  laboratory or one of WHOs regional quality
  assurance programmes.

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External Quality Assurance Procedure

• Procedure
• National reference laboratory sends to all
  participating laboratories a proficiency panel of
  6 specimens to identify as HIV- or HIV.
• Panels are tested at local laboratories in the
  same way as they routinely test their specimens
  for HIV.
• Local laboratories report their findings to the
  reference laboratory, which collates results and
  provides feedback.

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Warm Up Review

• Take a few minutes now to look back at your
  answers to the warm up questions at the beginning
  of the unit.
• Make any changes you want to.
• We will discuss the questions and answers in a
  few minutes.

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Answers to Warm Up Questions

• Which of the following is a factor in the
  decision to select an HIV testing strategy?
• sensitivity and specificity of test being used
• objective of the test
• HIV prevalence in the population being tested
• all of the above

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Answers to Warm Up Questions, Cont.
2. Match each phase of the HIV testing process
with the components it includes

• _b_ pre-analytical
• _c_ analytical
• _a_ post-analytical

• interpreting results, entering data into tracking
  system, reviewing quality control
• training, laboratory safety, selection of test
  kits
• specimen processing and storage, analysis of
  testing performance, reagent preparation

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Answers to Warm Up Questions, Cont.

• 3. The process by which reference specimens are
  tested externally to assure accuracy of a
  technicians or laboratorys performance is known
  as
• quality control
• quality assurance
• quality performance
• none of the above

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Small Group Discussion Instructions

• Get into small groups to discuss these questions.
  
• Choose a speaker for your group who will report
  back to the class.
• Take 15 minutes for this exercise.

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Small Group Reports

• Select one member from your group to present your
  answers.
• Discuss with the rest of the class.

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Case Study Instructions

• Try this case study individually.
• Well discuss the answers in class.

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Case Study Review

• Follow along as we go over the case study in
  class.
• Discuss your answers with the rest of the class.

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Questions, Process Check

• Do you have any questions on the information we
  just covered?
• Are you happy with how we worked on Unit 5?
• Do you want to try something different that will
  help the group?

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