◦
If the results remain indeterminate after one year, the person is considered to be
HIV antibody negative.
Pretest and posttest counseling services should be provided
.
Applications of ELISA
1.
In medicine for clinical diagnosis such as:
Tracking the spread of disease e.g. HIV, HBV, common cold, bird flu etc
Detecting antibodies in blood sample for past exposure to disease e.g. HIV
Detection of antigens e.g. p24, p120
2.
In food industry
Detection of potential food allergens
Detection of toxins in food
3.
Many other areas/fields
Rapid diagnostic tests (RDTs)
Basically involve antibodies testing
Many individuals do not qualify for ART because they do not know their HIV status.
It is important to know ones serostatus because:
i.
Clinical diagnostic purposes
ii.
It is the entry point for HIV prevention and care intervention
iii.
To protect blood supplies for donations
iv.
It identifies HIV-positive pregnant women for PMTCT
v.
Monitor disease trends in population
Rapid tests are visual tests that do not require the ELISA Reader.
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These tests are available in smaller test packs and therefore, are suitable for a laboratory
having smaller sample numbers.
They are technically simpler to perform although most of them have sensitivity and
specificity comparable to ELISA.
The commonly employed rapid anti-HIV antibody tests are based on the principles of dot
immunoassay, or particle agglutination such as gelatin or latex.
Summary of characteristics of rapid HIV tests for testing And counselling programmes
Accuracy
High sensitivity >99%
High specificity >99%
High reproducibility* >98%
■
Specimen type
Preferably for use on whole blood (fi nger-prick samples) for ease of collection
and to avoid the need for centrifugation
■
Little laboratory equipment required
■
No constant electricity or water supply required
■
Easy to perform
Little technical training required
Few steps
■
Easy to interpret
Visual interpretation of results, usually without equipment
Stable end-reading point
■
Rapid <
30 minutes
■
Easy to store
Storage at room temperature for several weeks (provided there are no significant
temperature fluctuations)
Shelf-life
12 months or longer
■
Number of tests performed
Suitable for individual and small volume testing, e.g. 1−40 samples per day
■
Minimal waste and waste disposal
■
Low cost
Mostly <US$ 1.0 for the initial screening
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ADVANTAGES OF RAPID TEST
Rapid tests enable decentralization of HIV testing and counseling acceptability of HIV
testing and counseling
Short time to obtain test result
Reduced cost
Ease of performance and ease of interpretation of test results
Minimal facilities for storage and shelf-life
Flexibility in numbers of tests performed
Reduction in occupational exposure risk
Pediatric HIV Diagnosis
