Suspected of having AIDS? Experts teach you to test correctly and check yourself quickly!

Author: Zhang Wei (Beijing Ditan Hospital, Capital Medical University)

When you suspect that you may have been exposed to HIV (Human Immunodeficiency Virus) and want to confirm whether you are infected, you should go to a professional health care facility for testing.

HIV antibodies or antigens, or HIV nucleic acids, are measured in blood, or other types of samples, to determine the presence or status of viruses and their active status.

In addition, we sometimes hear doctors say that "the initial screening is positive and needs to be further clarified by a confirmation test." What does this mean?

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1. What is the initial screening test?

After infection with HIV, the body produces "antibodies" that take about 3 weeks for HIV and its corresponding antibodies to appear in the bloodstream and be detected by existing conventional means.

HIV-1/2 antibody screening methods include enzyme-linked immunosorbent assay (ELISA), chemiluminescence or immunofluorescence test, rapid test (spot ELISA and spotted immunocolloidal gold or colloidal selenium, immunochromatography, etc.), simple test (gelatin particle agglutination test), etc.

Most medical institutions use the above test methods for initial screening testing. When HIV infection is present, more than 99% can show positive. However, sometimes the test results can be "false positive", that is, people who are not infected with HIV may also show positive test results, which is a limitation of existing technical means.

Therefore, a single test cannot be used to definitively diagnose HIV infection, and if positive, repeat testing with two different tests is used, if both are negative, they are reported as HIV antibody negative; if one yin and one yang or both are positive, further confirmation tests are required.

How are HIV test results understood? Normal: No HIV virus or antigens or antibodies are found.

If infected with HIV, HIV RNA can be detected in the blood at 1 week, antigens at 2 weeks, and antibodies at 3 weeks.

If the test is performed during the "window period" and the result is negative, HIV infection cannot be ruled out and the test needs to be repeated.

Negative viral load (nucleic acid) test at 2 weeks after high-risk behavior, negative for 4-generation antibodies (including antibodies good and antigen) for 4 weeks, and negative for 3-generation antibodies for 6 weeks to exclude infection.

Indeterminate: Test results do not clearly indicate whether hiv infection is present.

Possible causes are that the results are interfered with by some other infection, hormone, etc. If this happens, PCR can be performed to test for HIV viral load. If both viral loads are less than the detection threshold, HIV infection is generally not considered.

Abnormalities: HIV antibodies or antigens are found.

Using the same blood sample, repeated positive results by ELISA method or chemiluminescence must be confirmed by another test, such as an immunoblot test. If you are still positive, the infection can be basically confirmed.

2. What should I do if I am hive positive?

The initial screening may have a "false positive", and the initial hiv antibody screening "positive" does not necessarily mean that there is AIDS, but it can only be said that there is a suspicion of HIV infection, or the possibility of HIV infection is relatively large.

At this time, do not be too anxious, you should go to the local CDC or a laboratory with confirmation qualifications in a professional hospital to do HIV confirmation tests.

3. What is a confirmation test?

Confirmation test refers to the diagnostic method currently used to confirm HIV infection, and the main technical method is the western blotting test.

It has been reported that the specificity of the western blot test is not very good, with a "false positive" rate of about 2%, but it is still the most commonly used confirmation test for HIV infection.

If the results of the western blot test are "inconclusive", that is, it is not certain whether there is infection, HIV viral load testing, that is, polymerase chain reaction (PCR) testing, can also be used.

This test can detect the number of infected viruses (i.e., HIV RNA).

PCR testing is not as widely used as antibody testing because it requires strong technical skills and expensive equipment. This test can be done after 1 week of exposure to the virus.

Even if other tests are negative, the application of PCR may detect the RNA of the virus. PCR testing is very useful for detecting recent infections, i.e. shortening the window period.

When antibody or western blot test results are inconclusive, if two viral load tests are greater than the detection threshold, hive infection may be determined.

*The content of this article is a popularization of health knowledge and cannot be used as a specific diagnosis and treatment recommendation, nor is it a substitute for face-to-face consultation by a practicing physician, for reference only.

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