ppt2.hiv testing technologies
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HIV TESTING TECHNOLOGIES
HIV TESTING TECHNOLOGIES
Highly sensitive, specific, simple-to-use, rapid antibody tests that do not require sophisticated laboratory services, running water or electricity is an important advance
Testing can occur outside laboratory settings, does not require specialized equipment and can be carried out in primary health facilities by appropriately trained non- laboratory personnel, including counselors
Overview of HIV Testing
HIV tests detect antibodies or antigens associated with HIV in whole blood, saliva, or urine
Blood sampling is the most common method of testing
HIV tests are very accurate
Types of HIV tests
1. Antibody testELISAWestern Blot Rapid tests
2. Antigen test(HIV Viral Tests) p24 antigen test PCR (polymerase chain reaction) tests
DNA.RNA PCR
Antibody tests
After infection with HIV, the body makes antibodies to fight the virusIt may take 4 to 6 weeks, but occasionally up to 3 months for antibodies to become detectable in the bloodRapid HIV tests and the ELISA are the most common antibody tests
ELISA
99.5% sensitive, standard screening test Identifies antibodies to HIV infected pt.Highly sensitive but not always specific.Accurate only in pt over 18 month of ageDoes not detect “window period”Designed for large number of patientsIs not cost effective b/se all positive result should be confirmed by additional tests?
Limitations of the ELISA:
Tests must be done in batches of 4090Positive results must be confirmed with another ELISA or Western blotSpecimens sent to a laboratory for testing—results may take days to weeks Test requires refrigeration and specific reagents
Western Blot
Detects bands of protein specific to HIV antibody Negative in the absence of protein band Positive with the presence of protein band Confirmatory test.
Several rapid test detects HIV Anti body They share characteristics of ELISA Most of them are 99-100% sensitive and specific Specimen saliva, urine or blood Determine KHB (screening test)Capillus stat –pack test (confirmatory) Uni-Gold or serocard Tie breaker
Rapid tests
Accurate results within 20-40 minutesCan be done in the clinic settingNo batching required Limitation- under 18 month & window
period HCWs can be trained to perform the testsUsually do not require special equipment,
electricity or refrigeration
Rapid tests cont’d
Benefits of rapid HIV testing include
On-site testing and same day resultsLower risk of administrative errorAccepted by clientsFewer resources required:
Human resourcesResources at the facilityFinancial resources
Lower risk of occupational exposure
Rapid HIV Testing Algorithms
1. Serial testing2. Parallel testing
Serial testing
Blood sample taken and tested once If first test result is non-reactive, result is
given to client as HIV-negative If first test result is reactive, blood sample is
tested again using different brand of rapid test¨ If second test is reactive, result is reported as
HIV-positive¨ If second test is negative, a third test known as
a “tiebreaker” is performed
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Algorithm for Use of 3 Rapid Tests in Testing and Counseling Services
Pre-Test Education and/or Counseling
First HIV Rapid Test
Positive Test Result Negative test result/ Counsel for Negative Results
Second HIV rapid Test
Positive Test Result/Counsel for Positive Results
Negative Test Result
Third HIV Rapid Test
Negative Test Result/ Counsel for Negative Test
Result
Positive Test Result/Counsel for Positive Test Result
First HIV Rapid Test
Positive Test Result Negative test result/ Counsel for Negative Results
Positive Test Result/Counsel for Positive Results
Negative Test Result
Third HIV Rapid Test
Negative Test Result/ Counsel for Negative Test
Result
Positive Test Result/Counsel for Positive Test Result
Rapid HIV Testing(Serial testing)
First Test
Positive NegativeCounsel for Negative Result
Second Test
NegativePositiveCounsel for Positive
Result
Tie-breaker Test
PositiveCounsel for Positive
Result
NegativeCounsel for Negative
Result
Two HIV tests are performed on same sample at the same time, e.g., in parallel
If both are non-reactive, client reported HIV-negative
If both are reactive, client reported HIV-positive
If one is reactive and the other non-reactive, a “tiebreaker test” is performed
Parallel testing
Rapid HIV Testing(Parallel Testing)
Both Tests PositiveCounsel for Positive Result
Both Tests NegativeCounsel for Negative Result
Tie-breaker Test
PositiveCounsel for Positive
Result
NegativeCounsel for Negative
Result
First AND Second Test
Discordant
Interpreting HIV Antibody Tests
A positive HIV test Means that antibodies to HIV are present. It does not mean that the client has AIDSA negative HIV test :
The person is not infected with HIV, orThe person is infected with the virus but is in
the window period A negative test does not mean that person cannot become infected.
There is no such thing as immunity to HIV infection
Antigen test( HIV Viral Tests)
Viral tests detect the presence of HIV in bloodViral tests must be done by trained personnel
in the laboratory
p24 antigen test
Measures one of the HIV proteins used for
screening blood Infant diagnosis
PCR (polymerase chain reaction) tests
DNA.RNA PCR Highly sensitive and specific for HIV Used when the result of diagnostic tests are
unclear Antigen testing Most commonly utilized to diagnose HIV
infection in children <18 month RNA PCR detects and measures amount of virus
in blood (viral load)
Five Steps to HIV Testing
1. A specimen is obtained2. The specimen is processed 3. Test is conducted by a HCW or laboratory
technician 4. The client is told their result5. HCW provides post-test counselling, support
and appropriate referrals
Testing Procedure for HIV Infection
Infection control and Standard Precautions
Proper labelling Proper specimen
collection procedures Required volume per
test
Proper reagents per test
Correct timing per test Interpretation of resultsProper record-keepingProper disposal
procedures
Observe these points:
Testing Procedure for HIV Infection (Continued)
Factors affecting test performance: Storage and handling of test kits Changes in the environment Accuracy of equipment;
external and internal controls Shelf-life of the chemicals for the
tests (reagents) Technique for sample collection Quality of sample Use of equipment
Monitoring
Progress in implementationAssess effectiveness and impact (+ and -)
Access to testing and counselling, knowledge of serostatusUptake of prevention, treatment, care and support servicesMortality and morbidityHIV awareness and treatment literacySocial impact (e.g. rates of disclosure, discrimination, adverse outcomes)
Cost effectiveness, Quality of lab servicesReasons why PITC is performed