The human immunodeficiency virus (HIV) attacks and destroys immune system cells. If too many are lost, the body have trouble fighting off infections and other diseases. HIV is a lentivirus (a subgroup of retrovirus) that causes HIV infection and over time the acquired immunodeficiency syndrome (AIDS); 9-11 years average survival time after HIV infection, without treatment. According to statistics, around 29% of HIV-infected people are unaware of their status. Approximately 25% of HIV-positive people learn that they are infected at the time of an AIDS diagnosis.
+HIV infects helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through: pyroptosis of abortively infected T cells, apoptosis of uninfected bystander cells, direct viral killing of infected cells, and killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell number declines below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.
Most people with HIV don't have AIDS. People with AIDS have an extremely low number of immune cells, causing progressive failure of the immune system; they are at risk for life-threatening illnesses, such as dangerous opportunistic infections, severe pneumonia, cancers (Kaposi sarcoma). While there is no cure for HIV, the disease can be effectively controlled with medicines called antiretroviral therapy (ART). ART can significantly reduce the amount of HIV in the blood. People with HIV who take ART before the disease gets too advanced can live long, healthy lives. If one is living with HIV, it's important that the health care provider is seen regularly.
HIV is mainly spread through sexual contact and blood; there is high HIV infection risk if it is about:
- a man that has had sex with another man
- have had sex with an HIV-infected partner
- have had multiple sex partners
- have injected drugs, such as heroin, or shared needles with someone else.
HIV can spread from mother to child during birth and through breast milk (not through pregnancy ever since the female and baby's blood do not mix). If pregnant, the doctor may order an HIV test. The mother may be given medicines for pregnancy and delivery that greatly reduce risk of spreading the disease to the baby through the delivery process.
A negative test result may mean that one doesn't have HIV, but it may also mean that it is too soon to tell if there is infection. It may take a few weeks for HIV antibodies and antigens to show up in the body. If the result is negative, the health care provider should order additional HIV tests at a later date. There is a window (2-12 months after exposure) in which the immune system begins making antibodies against HIV. It's possible to get a negative test result within the first three months of being exposed to HIV. To confirm a negative status, one must be tested again at the end of the 3-months period. No test can detect HIV immediately after exposure. If there was exposure, getting a test the following day won't rule out infection. During the window period, a person may have HIV but still test negative. If the first test result is positive, a follow-up test to confirm the diagnosis is performed. If both tests are positive, it means one has HIV.
- nucleic acid tests (NAT)/HIV viral load
- antigen/antibody tests
- antibody tests
NAT/viral load test: the amount of virus in the venous blood; detects HIV sooner than the other tests, but is expensive (not routinely used as screening test, unless: high risk/possible exposure, early symptoms of HIV infection). It is mostly used for monitoring HIV infections. An HIV RNA PCR or NAT (nucleic acid amplification) may detect very early (acute) HIV infection, because HIV RNA appears in the blood within the first few days of infection. If the antibody test is negative but the NAT is positive, it may indicate that the patient is very newly infected. NAT testing is also used to confirm a positive result.
Antigen/antibody tests: HIV antigens (antigens: the foreign substances, part of the virus, triggering the immune system) and antibodies (antibodies: produced by the host's immune system in response to infection) in the blood. These tests usually find HIV within 2-6 weeks of infection and are one of the most common types of HIV tests. At HIV exposure, antigens (such as p24) show up in the blood before HIV antibodies are made. It is mainly performed on venous blood, but there are also finger prick antigen/antibody tests.
HIV antibody tests only search for the antibodies to HIV in blood/oral fluid. An HIV antibody test can determine if you have HIV from 3-12 weeks after infection, because it can take a few weeks or longer for the immune system to make antibodies against HIV. In general, antibody tests using venous blood can detect HIV sooner than those on finger prick blood/oral fluid. Most rapid tests (as well as the most tests approved as self-tests and the typical screening tests) are antibody tests.
The most commonly used testing for HIV are the rapid immunochromatographic tests on cassettes (mainly as antibody detection). The 2 pictures below show the principle of immunochromatography testing on cassettes ready and rapid to use.
Rapid immunochromatography test procedure:
Example of a rapid immunochromatography test: in about 10-20 minutes the device indicates whether HIV-1 or HIV-2 antibodies are present. If only one line appears on the strip (the control line that confirms the accuracy of the test functionality), it means that the person is not infected with HIV. If 2 lines appear, the person is likely infected. If the result is positive, a confirmation test must be performed. Again, it is important to mention that as with all antibody tests for HIV, it could take from 2 to 4 weeks for a newly infected person to develop antibodies to the HIV virus and thus test positive for HIV. Therefore, if there is a negative result but a possibility of a recent exposure to HIV, the test must be repeated.
To perform a rapid oral fluid/finger-prick blood test, the tester collects either oral secretions or a drop of blood from a finger-stick sample. For oral secretions, the device involves swabs once around both the upper and lower gums. The tester then inserts the device into a vial containing the developing solution (see image on the left for oral fluid tests).
Test kits usually have a certain shelf-life. False positives are possible with some rapid tests and have sometimes been associated with other conditions. Invalid tests may be repeated or tested using EIA and/or Western blot. And most importantly, reactive results should be considered preliminary and require confirmatory Western blot testing/other testing.
A negative result using a rapid HIV test should not be considered definitive (window period important). Some tests are capable of detecting HIV antibodies in as little as 14 days after infection. But for individuals who may have had a recent exposure, there is a need to recommend retesting in 3 months. If acute HIV infection is suspected, PCR or bDNA testing may also be warranted.
The results of the Western blot/other testing as confirmatory tests, once returned from the laboratory, are definitive in the event of a preliminary positive rapid HIV assay. In the event of a negative preliminary result, it is recommended to repeat with a confirmatory test to rule out the possibility of sample mix-up or evolving seroconversion. It also might be worthwhile to consider other diagnostic testing (which may give false positives with some rapid tests), such as hepatitis A, B, or C screening, rheumatoid factor, EBV infection, and also HIV PCR if there was the possibility of a recent exposure to HIV.
If preliminary testing showed positive but the confirmatory proved negative, retesting should be performed at the end of the 3-months period. The most likely scenario, after a preliminary positive rapid assay, is that the confirmatory testing will also be positive. In this case, the HIV positive diagnosis is definitive.
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