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For Surveillance of HIV infection in the population
For Screening of blood and blood products
Sensitivity and specificity of the test being used
Prevalence of HIV infection in the population where the test is being used
Tests that can be used
Serological methods: antibody/antigen based test
Enzyme Immunosorbent Assay (ELISA)
Viral detection methods
Culture: Rarely used
Common and widely used tests
Based on the principal of antigen antibody reaction
Antibody takes some time to be produced after an infection
Therefore all these tests have a problem of making a diagnosis during the period immediately after infection with HIV prior to the appearance of detectable antibodies
“ Period of time between the onset of infection with HIV and the appearance of detectable antibodies”
Sensitivity of the test kit (ability to detect low levels of antibodies)
The duration the body takes to produces antibodies (5-7 days) after infection
The level of antibodies produced (low levels during early infection).
Over 40 different kits available
Have relatively simple methodology
High sensitivity of 99.3-99.7% and high specificity of >99.7%
Suitable for testing large samples
Detect both HIV-1/2 antibody
Developed in the late 1980s
Can be performed in less than 20 minutes
therefore also referred as “Simple/Rapid” (S/R) assays
Can be performed easily without instruments
A positive result is indicated by the appearance of a colored dot or line
Examples – Determine, Unigold and Oraquick.
All positive tests should be confirmed with another test
Not usually necessary to confirm negative tests
There are very specific assays that are used to verify positive HIV results e.g. Western Blot
Designed to identify individuals who are not infected but who have reactive screening test results
High specificity- therefore produce few false-negative results
Alternative Confirmatory Strategies
Developed by UNIADS/WHO for use in confirming initial HIV positive tests
maximizes accuracy while minimizing high cost associated with Western Blot but retaining similar predictive values to Western blot and others.
Three testing strategies recommended by UNAIDS/WHO
Strategy used depends on purpose of the test and the prevalence of HIV in the population
The strategy used works on the principle of using two screening tests either in parallel or sequentially
Report sensitive Consider +ve A +ve -ve specific B +ve -ve sensitive A +ve -ve Report Indeterminate Report sensitive C +ve -ve + - - Low risk A +ve -ve sensitive specific B +ve -ve Report Report TRANSFUSION TRANSFUSION SURVEILLANCE DIAGNOSIS DIAGNOSIS I II III WHO HIV antibody testing strategies + - + High risk Sensitivity >97% Specificity >95% SERIAL TESTING PARALLEL TESTING
HIV tests are highly sensitive.
A positive HIV tests will be sometimes obtained in absence HIV infection (no HIV antibodies in the blood) referred as a “false-positive”
Influenza immunization may temporarily cause a false-positive
Autoimmune diseases - RA/SLE
Identified by additional testing.
All positive results must be confirmed by another test method.
A confirmed positive result from the second test method means that the individual is infected with HIV.
This is a negative HIV test results in an HIV infected person ( where the HIV test should have been positive).
newly infected patient at the window period
No HIV antibodies are yet being produced
End stage of HIV
Prolonged immune reconstitution with HAART
Atypical host response
Type N or O strains or HIV-2 (ELISA 20-30% FN in HIV-2)
If it occurs in high-risk patients, repeat the test after a time before reassuring the person that they are not infected with HIV
Occurs when 2 different testing kits gives different results (-/+ or+/-)
Causes of Indeterminate results:
in people with clinical signs meeting WHO criteria 3, stages III or IV.
During sero-conversion phase
Infection with O strain or HIV-2
HIV vaccine recipients
Technical or clerical error
How to handle indeterminate results
Obtain and test a second sample after a minimum of 2 weeks in asymptomatic individuals
test the second sample using the appropriate strategy and if indeterminate use confirmatory assay.
If confirmatory test result is also indeterminate, follow-up the person for a longer period (3 to 12 months).
If the results remain indeterminate after one year, the person is considered to be HIV-negative.
Unit 5B: Laboratory Monitoring and Follow-Up
CD+4 absolute counts
CD4+ T-Cell Counts
CD4 cells have a central role in the function of immune system.
Reduced number and quality of CD4 cells causes a weakened immune system
The level of CD4 cells used to measures the strength of the immune system.
Monitoring ARV Therapy
Normal values ranges from 500-1400 cells/ml of blood
With ART the median increase in CD4 count is 100 to 150 cells per year.
Magnitude of increase in CD4 cells depends on the baseline CD4 count and adherence to the ARV.
A reasonable frequency of CD4 count measurements in patients on antiretroviral therapy is every 6 months.
Factors Affecting CD4 Count
Diurnal variation: low in the morning and high in the afternoon- stick to specific time appropriate for each patient
Active infections including Opportunistic Infections :therefore, treat OI’s before checking CD4 Count
Use of CD4 T cells in HIV management
Prognostic indicator in HIV disease
Benchmark for initiating prophylactic medications and ART
Guidance on the management of asymptomatic patients
Information on the efficacy of ARVs
Use of Viral load and resistance testing
Not widely available
May become increasingly available in future
Assessment of circulating HIV RNA load
Has a prognostic value
at any CD4 count the higher the viral load the faster the disease progression (decline in CD4 count)
Current use of viral load
Not currently recommended in general patient management
Current guidelines may change in future as the tests becomes more widely available and affordable
Early detection of new HIV infection
Diagnosis in children < 18 months
Determine response to therapy
Determine treatment failure
Deciding when to initiate therapy
Initiation of HAART currently based on WHO Stage and CD4 count
Expensive and not generally available in many countries.
Can be used to identify drugs the HIV is resistant to.
Helps in the management of patients who have failed treatment, to select new ARVs where there is resistance
Recommendation: in research settings
Other tests: Hematological tests
anemia before AZT
Bone marrow suppression during ARV
White blood cell counts and differentials
High WBC level may signify infection
Low WBC may indicate disease progression or bone marrow suppression (cotrimoxazole)
TLC <1200/ml has been correlated with CD4 count<200 cells/ml
TLC should not be used make decisions on initiation of ARV in asymptomatic patients
Others tests: Biochemistry tests
Serum alanine or aspartate aminotransferases
Assesses possible hepatitis co-infection
Monitors for liver toxicities from ARV
Serum creatnine +/ – blood urea nitrogen
Baseline renal function
Possible renal toxicity
Hyperglycemia and diabetes in PI based regimen
To rule out pregnancy and avoid drugs contraindicated in pregnant such as Efavirenz
Elevation associated with PI regimen (Indinavir, Atazanavir )
Lipids (cholesterol, triglycerides)
Elevation in PI based regimen, d4T
Others tests: Biochemistry tests
For screening of syphilis
Evaluation of possible active TB
Pap smear/VIA or VILI
Screening cervical cancer
cervical cancer an AIDS indicator
Commonest cancer in women
Regular screening recommended in HIV+ women
HIV infections cause production of antibodies and viral products which can be used to make a diagnosis
EIA long and rapid tests are commonly used for diagnosis of HIV
CD4 counts can be used as a guide for initiating prophylactic medications and ART, to provide information on the efficacy of ARVs and to monitor HIV progression
Viral load tests can be used for early detection of new HIV infection, for determination of response to therapy and sometimes for when to initiate therapy