What are my HIV testing options?
Next combo tests offer faster, more reliable results
When an HIV infection is suspected, it is most commonly diagnosed by tests that can detect cells called antibodies and/or antigens in either the blood or saliva.
An antibody is a type of protein secreted by white blood cells that can detect and destroy foreign bodies like viruses or bacteria. An antigen, by contrast, is any substance that can provoke an immune response in the form of antibodies (as happens with HIV).
The tests used to confirm HIV infection are designed to react with these agents. A “positive” result means that HIV antibodies/antigens have been detected and that an infection has occurred. A “negative” result means that no antibodies/antigens have been detected and that HIV infection has not occurred.
Conversely, a “false positive” is when a test incorrectly indicates an HIV infection, while a “false negative” is when the test incorrectly shows that no infection has occurred. Both of these are relatively rare are using current testing assays.
Understanding the window period
People will usually develop measurable levels of HIV antibodies within 30 days of infection, although some may take longer—up to three months in some cases. HIV antigens, by contrast, take between two to five weeks to develop.
Before this happens, there is a period wherein antibody/antigen levels are too low to be reliably detected.
This is called the window period. It is during this time that an infected person can pass HIV to others, but still have a negative result if given an HIV test.
If you believe you have been infected and suspect when you might have been accidentally exposed to HIV, it’s important that you share this with your doctor or testing center.
They can then help determine if the HIV test falls within the window period or if it can be performed with reasonable levels of reliability.
HIV antibody tests
The HIV ELISA (enzyme-linked immunosorbent assay) is a highly sensitive test that changes color when HIV antibodies are present. Results are assigned a numeric value, with values below 1.0 indicating a negative result and values above 1.0 indicating a positive (or reactive) result. Although the ELISA offers a high probability of HIV infection, it is not used alone as in the detection of HIV.
When an ELISA test produces a positive result, a second antibody test, called the Western Blot, is used to confirm the results. Together, the ELISA and Western Blot are shown to have an accuracy of 99.9 percent in the general U.S. population, with a false-positive rate of about one out of every 250,000 tests performed.
Occasionally, the tests can return with an indeterminate or inconclusive result. This can happen for a number of
The infection may have been too recent to reliably detect.
There may have been problems with the test sample or the testing procedure itself.
Acute infections like syphilis ?or Lyme’s disease can sometimes elicit a false positive result, as can autoimmune conditions like lupus or diabetes.
If a person has an inconclusive result, the tests should be repeated.
Combination antigen/antibody tests
On June 27, 2014, the Centers for Disease Control and Prevention recommended a new strategy for HIV testing using 4th generation combination assays. These next generation tests are able to test for both HIV antibodies (Ab) and antigens (Ag) and can confirm an HIV infection up to four weeks earlier than ELISA/Western Blot assays.
There are two such tests approved by the U.S. Food and Drug Administration for use in HIV screening: the Alere Determine HIV 1/2 Ag/Ab Combo and the Abbott ARCHITECT HIV Ag/Ab Combo.
Based on their high level of testing accuracy, the CDC recommends the following three-step approach:
Conduct initial testing with Ag/Ab combo assays. If the result is negative, then no further testing is needed.
If the first result is positive, conduct a second test to differentiate HIV-1 and HIV-2 antibodies, a step considered important in determining the course of therapy for the HIV-infected individual.
If the second result is negative, a third test (called the HIV-1 NAT) would be performed to differentiate acute HIV1 infection from an initial false positive result. The HIV-1 NAT is able to detect small quantities of viral RNA is as little as one to two weeks.
Due to the reliable combination of Ag/Ab testing, confirmation by way of a Western Blot is no longer considered necessary.
Rapid in-home HIV tests
Rapid in-home HIV tests are ELISAbased assays that can deliver results in as a little as 20 minutes (as opposed to standard ELISA/Western Blot assays that can take several days). The tests are performed using saliva samples, the results of which can either be “negative” or “preliminary positive.” Preliminary positives must be confirmed with a Western Blot performed in a lab.
In 2012, the FDA approved the first in-home rapid HIV test for direct sale to consumers. While the products are easy to use and offer linkage to care for those who do test positive (via a 24-hour consumer hotline), some are concerned that the lack of face-to-face counseling and potential breaches in informed consent may undermine prevention efforts.
Furthermore, while the in-home tests offer the same sensitivity and specificity as point-of-care tests, clinical research has demonstrated a false negative rate of around seven percent (or roughly one out of 12 tests).
Another study published by the University of California, San Francisco has suggested that fourth generation rapid tests have a real-world accuracy of around 86 percent in correctly identifying HIV-positive cases but only 54 percent accuracy in confirming serostatus during the early, acute stages of HIV infection.
With mounting evidence suggesting that early diagnosis and treatment may prevent a number of long-term complications — including a possible reduction in the viral reservoirs where HIV can persist for decades — the need for accurate identification during acute infection is considered imperative.
The window period is the time that an infected person can pass HIV to others, but still have a negative result if given an HIV test.