Study Shows That Some Tests Fall Short In Early Infection
As the United States aims to increase early diagnosis and treatment of people with HIV, a greater focus has been placed on determining the accuracy of HIV tests in real-world settingsnot only to minimize the number of false positive or negative test results, but to better identify people during the early stages of infection when the risk of transmission is especially high.
In order to do this, researchers from the University of California, San Francisco conducted a review of over 21,000 HIV tests performed between the years 2003 and 2008 in some of the city’s high-prevalence populations.
Of four types of tests used during this periodfrom first-generation antibody tests to rapid oral tests761 people were diagnosed with HIV , while 58 were identified during acute infection.
The study also aimed to compare the accuracy of newer testing assaysincluding fourth-generation antigen/antibody testsby retesting the blood from the 58 people previously diagnosed with acute HIV infection.
As accuracy is related to sensitivity and specificity , the take-home message is that there is room for improvement in HIV testing to capture more acute infection.
What Is The Window Period
The window period is time between HIV infection and the point when a test will give an accurate result. Different types of tests have different window periods.
- 4th generation antibody/antigen tests: 45 days.
- 3rd generation antibody only tests: 60 days.
- Point of care tests (self-sampling, self-testing and rapid tests: 90 days.
During the window period a person can have HIV and be very infectious but still test HIV negative.
UK guidelines recommend a window period of six weeks for a 4th generation antigen/antibody test. By this time 99% of infections will be detected . Testing after only four weeks will detect 95% of infections.
A negative result at 6 weeks with a 4th generation test does not need to be confirmed.
A negative result from testing earlier, for example after four weeks, needs to be confirmed by a second later test.
How Soon Can A Blood Test Detect Hiv
The window period is when a person is first exposed to HIV and when the virus will show up on types of HIV blood tests.
The window period can last 10 to 90 days, depending on their bodys immune response and the type of test that theyre taking.
A person may receive a negative test result during the window period even though theyve contracted HIV.
A person can still transmit HIV to others during this window period. Transmission may even be more likely because there are higher virus levels in a persons body during the window period.
Heres a quick breakdown of the types of HIV tests and the window periods for each.
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How Accurate Are Hiv Tests
Some tests can detect HIV within 10 days of exposure, but detection ultimately depends on how quickly ones immune system reacts to the virus. For some people, detection could take months.
Accuracy of a negative test result depends on a persons body and the type of test that was used. There are a number of HIV tests that have been developed since the virus was first detected in the 1980s.
Each test has whats called a window period, or the time between contact with the virus and when the virus can be detected in the body.
The window period is different for each test and person. Ask a healthcare professional about the window period for your specific test.
Newer laboratory tests work to detect antibodies to HIV as well as a viral protein called p24 to detect an infection. Because p24 can appear before antibodies to HIV, antigen/antibody tests have a tighter window period than older tests for antibodies alone.
In fact, the newest types of antigen/antibody tests are 99 percent conclusive within 44 days of exposure.
Is The Combo Test After 6 Weeks Correct
If conventional testing methods take 2-3 months to give accurate results, with the HIV test method the time is shortened. After 6 weeks it can be determined quite accurately whether you have HIV or not.
If the routine test is in the early stage of infection when the concentration of HIV in the blood is not high, the detection of p24 antigens is difficult, usually only detecting HIV antibodies when the virus has developed.
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Facts You Should Know About The Rapid Hiv Test
It is now clear from a number of studies that getting treatment as soon as possible after becoming infected with HIV is better than waiting. HIV-infected patients who are treated early have fewer complications from HIV infection and are less likely to infect other people than those who wait to be treated. Studies also show that people who know they are HIV-positive may change their behavior to decrease the risk of infecting others.
The U.S. Centers for Disease Control and Prevention now recommends that all people between the ages of 13 and 64 get tested for HIV regardless of risk.
HIV testing is also recommended at least once a year for those at higher risk of getting HIV infection. These include
- people who use injection drugs and share needles or syringes
- people who have unprotected sex with men who have sex with men , or with people who have sex with multiple partners or anonymous partners
- people who exchange sex for drugs or money
- people who have been diagnosed with hepatitis, tuberculosis , or an STI such as chlamydia, gonorrhea or syphilis and
- people who have unprotected sex with someone with any of the above risk factors.
What Are The Different Types Of Hiv Tests
The window period and accuracy for HIV testing varies by test and the bodys individual immune response. The following are types of HIV tests, window periods for each, and accuracy information.
Generally, tests that use blood from a lab draw deliver accurate results sooner than tests that use finger pricks or oral swabs.
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Are Hiv Tests Accurate
Yes. Modern HIV tests are very accurate.
This accuracy has to be considered with the window period.
For example, 4th generation tests will pick up 99% of infections at six week.
Testing earlier, for example after four week, only detects 95% of infections. Testing earlier needs a confirmatory test three months after the risk.
A positive test result is routinely confirmed using a different type of test called western blot. The western blot test looks for immune responses to specific HIV proteins and is 100% accurate as a confirmatory test.
Can anything affect the result of my HIV test?
HIV antibody tests, confirmed by the second test, are not affected by other circumstances.
This includes infections, medications, most vaccinations, putting on weight, eating or drinking anything before the test, use of alcohol or recreational drugs, mouthwash or time of day.
Your test result is accurate even if you had flu or a cold or are using any medication.
You do not need to fast before your test. Food and drink do not affect the results.
Rapid/point Of Care :
- Blood is drawn by a finger prick and tested on the spot. This procedure usually takes about 40 minutes.
- Results will be given to you during the same visit.
- If the test result is positive, a standard blood draw is done as described on the previous page to confirm the positive result.
- A clinician should always get your consent before testing you.
- Both tests are 99.5% accurate for any sexual acts/shared needle use that took place more than 3 months prior to having the test.
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What Should I Do If My At
If you use an at-home rapid HIV test and get a positive result, you should immediately contact your doctor. They will likely recommend that you get a second test from a healthcare professional to confirm the results. False positives are a possibility, so you will want to confirm the tests results.
If you are at high risk of HIV, your best option is to talk to a doctor about taking PrEP. This will protect you from the risk of HIV transmission. PrEP is a medication regimen that can reduce the risk of HIV transmission by up to 99% when taken as directed.
Should I Tell Anyone Else Of My Test Results
Yes. If you test positive for HIV infection, it is important that you tell your healthcare practitioners as well as all current and future sex partners and/or anyone with whom you share needles. Counseling services are often available from the clinic that performed the test or from your healthcare provider that will help you to inform the people who need to know.
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Window Periods Of Rapid Tests
The window period refers to the time after infection and before seroconversion, during which markers of infection are still absent or too scarce to be detectable. Tests cannot reliably detect HIV infection until after the window period has passed. All tests have a window period, which varies from test to test.
Delaney and colleagues estimated window periods for a handful of rapid tests in a 2017 study. However, all these estimates were based on testing blood plasma. In practice, tests are usually done on fingerprick blood and the window period is likely to be several days longer.
The fourth-generation Determine HIV-1/2 Ag/Ab Combo was estimated to have a median window period of 19 days . This indicates that half of all infections would be detected between 15 and 25 days after exposure. Ninety-nine per cent of HIV-infected individuals would be detectable within 43 days of exposure.
The third-generation INSTI HIV-1/HIV-2 test was estimated to have a median window period of 26 days . This indicates that half of all infections would be detected between 22 and 31 days after exposure. Ninety-nine per cent of HIV-infected individuals would be detectable within 50 days of exposure.
UK guidelines take a cautious approach, describing the window period for all rapid, point-of-care tests as 90 days.
Hiv Tests For Screening And Diagnosis
HIV tests are very accurate, but no test can detect the virus immediately after infection. How soon a test can detect HIV depends on the type of test being used. There are three types of HIV tests: antibody tests, antigen/antibody tests, and nucleic acid tests .
An initial HIV test usually will either be an antigen/antibody test or an antibody test. If the initial HIV test is a rapid or self-test and it is positive, the person should go to a health care provider to get follow-up testing. If the initial HIV test is a lab test and it is positive, the lab will usually conduct follow-up testing on the same blood sample as the initial test. Although HIV tests are generally accurate, follow-up tests allow the health care provider to confirm the result.
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What Is It Used For
An HIV test is used to find out if you have been infected with HIV. HIV is the virus that causes AIDS . Most people with HIV don’t have AIDS. People with AIDS have an extremely low number of immune cells and are at risk for life-threatening illnesses, including dangerous infections, a severe type of pneumonia, and certain cancers, including Kaposi sarcoma.
If HIV is found early, you can get medicines to protect your immune system. HIV medicines may prevent you from getting AIDS.
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What Do The Results Mean
If your result is negative, it can mean you don’t have HIV. A negative result may also mean you have HIV but it’s too soon to tell. It can take a few weeks for HIV antibodies and antigens to show up in your body. If your result is negative, your health care provider may order additional HIV tests at a later date.
If your result is positive, you will get a follow-up test to confirm the diagnosis. If both tests are positive, it means you have HIV. It does not mean you have AIDS. While there is no cure for HIV, the disease can be effectively controlled with medicine. The medicine used to treat HIV is called antiretroviral therapy . 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 you are living with HIV, it’s important to see your health care provider regularly.
How Accurate Is An Hiv Test After 2 Weeks
It will depend on the type of HIV test. Generally speaking, HIV tests are highly accurate when theyre performed correctly and after the proper window period.
An antibody test may not be accurate after 2 weeks because it typically takes the body a few weeks or even months to produce HIV antibodies.
An antibody/antigen test can technically detect HIV in as little as 18 days, or about 2.6 weeks.
According to a 2017 study, only 25 percent of people with HIV will receive a positive test result within 13.0 to 14.8 days of taking an antibody/antigen test. After 17.8 to 19.2 days, that ratio improves to 50 percent. After 43.1 to 44.3 days, the test will detect HIV in 99 percent of HIV-positive people.
An RNA test can detect HIV in 10 to 14 days, according to the San Francisco AIDS Foundation. The National Cancer Institute states that an RNA test can detect HIV .
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How Confidential Are Hiv Test Results
Your HIV status, like other medical conditions and test results, is protected by the HIPAA Privacy Rule and cannot be shared with friends, family, or employers without your written permission. Your HIV status may be shared with your healthcare providers who have a “need to know” in order to treat you. Also, in order to determine the incidence of HIV and to provide appropriate prevention and care services, all new cases of HIV are reported to state and local health departments.
Certain testing centers provide either anonymous or confidential HIV testing and counseling. You can also contact your state or local health department to find out where testing may be available.
Timing Of Serological Testing In Infants
The most recent advances in EIA technology have produced combination assays, which allow for the simultaneous detection of p24 HIV antigen and HIV antibodies. This approach has further shortened the window period, i.e. the interval between HIV infection and detectable HIV antigen/antibodies. Rapid tests appear to offer similar performance characteristics but they detect antibody 28 days later than third-generation EIAs.
All children born to HIV-infected mothers carry detectable maternal HIV antibody and this declines slowly over the first year of life. The rate of decay of maternal antibody has been ascertained largely by analysis of studies to detect HIV antibody in children who have not been breastfed. The mean and/or median age at the time of seroreversion ranges between 9 and 16 months of age in studies from both developed and developing countries . These data indicate that maternal antibody may remain detectable through the first 6 months of life but significant decay occurs by 912 months of age. Most HIV-uninfected children do not have detectable antibody at 12 months of age .
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Generations Of Hiv Antibody Tests: When They Can Be Done And Their Accuracy
This table summarizes four generations of HIV Ab teststhat currently can be performed. They all confirm seroconversionâthe bodyâs response to the virus via production of antibodies.
*Please note that with each generation, the test has become more accurate sooner.
|HIV Ab tests|
|15â20 days post exposure 50% accuracy||44 days post exposure is 99% accurate|
How Is The Test Used
HIV tests are used to screen for and diagnose HIV infections.
Different types of tests may be used for HIV screening:
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