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