HIV Test after 18 days : which test to do
Learn which test has the best chance of diagnosing an HIV infection , 18 days after exposure. In depth analysis of 3rd generation, 4th generation and RNA PCR tests as well as their likelihoods of showing positive.Published Date : 2023-09-09T20:54:05.696Z
Updated Date : 2023-09-09T20:54:05.696+00:00
Table of Contents
How does the HIV virus multiply inside the body
What viral particles are in the body around 18 days after exposure?
What is a window period?
Which are the different tests that can be done to detect HIV?
Will a 4th generation lab based test detect HIV at 18 days?
Will a 4th generation Point of Care based test detect HIV at 18 days?
Will a third generation lab based assay detect HIV at 18 days?
Will a third generation point of care based assay detect HIV at 18 days?
Will a RNA PCR test detect HIV at 18 days?
What is the confirmatory test for HIV at 18?
References
How does the HIV virus multiply inside the body
As individuals encounter the HIV virus, its replication takes root within submucosal cells. The virus establishes interaction with CD4 helper T cells, which hold a crucial role in the immune system. Subsequently, viral RNA, carrying the virus's genetic code, infiltrates these CD4 cells. The viral RNA is then altered into viral DNA using reverse transcriptase. This introduced viral DNA takes charge of the cell's internal mechanisms, guiding them to generate an augmented quantity of viral particles. Ultimately, the infected cell attains its limit, leading to its rupture and the dissemination of newly formed virions into the bloodstream.
What is a window period?
The window period encompasses the initial weeks or months after HIV infection, when viral replication is high but the immune response has not yet reached levels detectable by tests.
Which are the different tests that can be done to detect HIV?
The detection of HIV incorporates a range of testing strategies, each targeting specific components of the virus. This includes tests that zero in on the p24 antigen, antibodies such as IgM and IgG, and the application of RNA PCR for superior sensitivity.
Third Generation Tests
3rd generation tests are so called because they detect antibodies to the HIV 1 and HIV 2 strains. These tests are available in two formats - lab based automated assays, which automate the processes of pipetting and dispensing and point of care assays that can be done using standard manual pipetting.
| Test Type | Description | Test Names |
|---|---|---|
| 3rd Generation | 3rd generation tests detect antibodies against HIV. |
|
Fourth Generation Tests
4th generation tests are so called because they detect both the HIV P24 antigen as well as antibodies to the HIV 1 and HIV 2 strains. These tests are available in two formats - lab based automated assays, which automate the processes of pipetting and dispensing and point of care assays that can be done using standard manual pipetting.
| Test Type | Description | Test Names |
|---|---|---|
| 4th Generation | 4th generation tests detect both antigen and antibodies. |
|
Will a 4th generation lab based test detect HIV at 18 days?
There is a moderate chance of a 4th generation lab based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - p24 antigen, IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
A 4th generation HIV test is an up-to-date diagnostic approach that detects the p24 antigen and both IgM/IgG antibodies together in a single test, enhancing accuracy..Lab based assays as described above are fully automated and are considered to be one of the most sensitive tests for early diagnosis of HIV. If you were exposed to HIV, there is a 41.8% chance that the 4th generation lab based assay will be able to detect the virus at 18 days. This is based on the varying levels of the p24 antigen as well as the time it takes for the antibodies to develop in the body agains the virus. It is recommended that you retest after some days since the chances of detecting HIV increase with time.
There is a moderate chance of a 4th generation lab based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - p24 antigen, IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
Will a 4th generation Point of Care based test detect HIV at 18 days?
There is a moderate chance of a 4th generation point of care based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
.Point of care assays as described above are generally performed with methods like lateral flow immunochromatography and are well suited for low resource and bedside settings. These assays have now achieved comparable results to lab based assays. If you were exposed to HIV, there is a 40.5% chance that a 4th generation point of care based assay will be able to detect the virus at 18. This is based on the varying levels of the p24 antigen as well as the time it takes for the antibodies to develop in the body agains the virus. It is recommended that you retest after some days since the chances of detecting HIV increase with time.
There is a moderate chance of a 4th generation point of care based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
Will a third generation lab based assay detect HIV at 18 days?
There is a moderate chance of a 3rd generation lab based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
An established diagnostic approach, the 3rd generation HIV test detects both IgM and IgG antibodies against the virus, aiding in its timely identification..Third generation assay only test for the IgM and IgG antibodies, as such the latency for positivity with these assays is greater. Third generation lab based assays use automation in various steps of the test and as such are considered to be more accurate than the point of care tests, however they require more expensive equipment. If you were exposed to HIV, there is a 37.5% chance that a 3rd generation lab based assay will be able to detect the virus at 18 days. This is based on the time it takes for the antibodies to develop in the body agains the virus. It is recommended that you retest after some days since the chances of detecting HIV increase with time.
There is a moderate chance of a 3rd generation lab based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
Will a third generation point of care based assay detect HIV at 18 days?
There is a moderate chance of a 3rd generation point of care based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
.Third generation assay only test for the IgM and IgG antibodies, as such the latency for positivity with these assays is greater. Third generation point of care based assays use lateral flow chromatography or similar techniques and are suited for low resource settings. If you were exposed to HIV, there is a 29.9% chance, that a 3rd generation point of care based assay will be able to detect the virus at 18 days. This is based on the time it takes for the antibodies to develop in the body agains the virus. It is recommended that you retest after some days since the chances of detecting HIV increase with time.
There is a moderate chance of a 3rd generation point of care based test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
This is because the analytes measured by this test, namely - IgM and IgG antibodies are not yet present in adequate concentration in your blood by day 18 of the infection.
Will a RNA PCR test detect HIV at 18 days?
There is a relatively high chance of a RNA PCR Molecular Test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
RNA PCR assays can detect viral loads as low as 20 copies of viral RNA/ml. RNA PCR assays can detect the virus as early as 10-12 days, and almost all patients will show positivity between 20-30 days.Based on the fact that you have been exposed 18 days ago, there is a 74.9% chance of the RNA PCR test being able to detect the virus.You should retest after some days, for confirmation.
There is a relatively high chance of a RNA PCR Molecular Test being able to detect the virus in your body on day 18 after exposure to the HIV virus.
What is the confirmatory test for HIV at 18?
There is no 100% confirmatory test for HIV. Any negative test is recommended to be repeated after 45-90 days. Positive tests are usually reconfirmed on repeated sampling in accordance with the guidelines of your country's health organizations. While the RNA PCR test usually has the highest chance of detecting the virus, it is never recommended as a first line test, owing to its cost and complexity. A first line screening test is usually done (4th generation) and if it is positive, additional testing is recommeded.
References
- Hurt CB, Nelson JAE, Hightow-Weidman LB, Miller WC. Selecting an HIV Test: A Narrative Review for Clinicians and Researchers. Sex Transm Dis. 2017 Dec;44(12):739-746. doi: 10.1097/OLQ.0000000000000719. PMID: 29140890; PMCID: PMC5718364.Hurt et,al
- Kevin P. Delaney and others, Time Until Emergence of HIV Test Reactivity Following Infection With HIV-1: Implications for Interpreting Test Results and Retesting After Exposure, Clinical Infectious Diseases, Volume 64, Issue 1, 1 January 2017, Pages 53–59,Delaney et.al
Reviewed By - Dr.Bhargav Raut
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