FALSE POSITIVES AND NEGATIVES IN HIV TESTS
With the advent of modern testing methods, the number of false positives and negatives in HIV testing has reduced drastically. However, there are some cases where they still occur. Generally, they occur more commonly in anti-body based tests and false negative results are less common.
The ability of a test method to detect only HIV is called SPECIFICITY, while it ability to detect even minute quantities of the viral particles or antibodies is called SENSITIVITY.
Specificity deals more with its ability to give less false positive or negative results, while sensitivity deals more with its ability to detect HIV earlier when it is present.
Generally, two tests at least are recommended to make a definitive diagnosis of HIV; the initial test and a confirmatory test. If both are positive, then the person is positive and may require differentiation assay (to know whether its HIV 1 or/and 2), then a nucleic acid based test or/and ELISA is used to know the serotypes and viral load.
False positive result means the individual does not have the virus but tests positive in the tests. Some causes are:
- Recent immunization with influenza vaccine
- Auto-immune disorders
- Prior blood transfusions
- Recent viral infections
- Receipt of an investigational HIV vaccine
- Receipt of gamma globulin
- Collagen vascular diseases
- Human T-lymphotropic virus 1 and 2 infections
- Laboratory or technical errors
- Chronic alcoholics
- Liver cirrhosis
False negative result is a negative HIV test in a person that actually has the virus. Some of the causes are:
- Persons still in the window period
- Laboratory or technical errors e.g. expired strips
- Persons who took potent anti-retro viral drugs immediately after exposure to the virus
- Persons who have defect in HIV immunity
- People on pre-exposure prophylaxis
- Natural HIV controllers
- Persons with Hypogammaglobulineamia
- Persons who recently received potent immunosuppressive drugs
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