What is HIV Testing?

Laboratory tests for AIDS include HIV antibodies, HIV nucleic acids, CD4 + T lymphocytes, and HIV genotype resistance tests. HIV1 / 2 antibody detection is the gold standard for the diagnosis of HIV infection; HIV nucleic acid quantification (viral load) detection and CD4 + T lymphocyte count are two important indicators for judging disease progression, clinical use, efficacy and prognosis; HIV genotype resistance Drug testing can provide scientific guidance for the selection and replacement of highly effective antiretroviral therapy (HAART) protocols.

Basic Information

English name

detection of acquired immune deficiency syndrome

Visiting department

Infectious Diseases

Multiple groups

HIV-infected patients

HIV testing methods

1. HIV1 / 2 antibody and antigen detection

Including screening tests (including initial screening and retesting) and confirmation tests. HIV1 / 2 antibody screening methods include ELISA, chemiluminescence or immunofluorescence tests, rapid detection (spot ELISA and spot immunocolloid gold or colloidal selenium rapid test, gelatin particle agglutination test, immunochromatographic test), etc., confirmation tests are commonly The method is western blotting.

A negative test for a screening test can produce a negative HIV1 / 2 antibody report. It is found in individuals who are not HIV-infected, but a screening test for a newly infected person in the window period can also be negative. If it is positive, repeat the test by using the original reagent and another reagent from a different principle or from a different manufacturer, or repeat the test from another reagent from a different principle or from a different manufacturer. If the two tests are negative, HIV antibodies are negative; if one or two reagents are positive, an HIV antibody confirmation test is required. The confirmation test did not produce HIV-specific bands and reported HIV1 / 2 antibody negative. The confirmation test showed HIV1 / 2 antibody specific bands, but it was not enough to determine positive. Reporting of HIV1 / 2 antibody was uncertain and could be followed up after 4 weeks. If the banding does not progress or is negative, report a negative result; if banding progresses during the follow-up period and meets the HIV antibody positive determination criteria, the HIV antibody is positive. If the banding still does not meet the positive criteria, continue to follow up to 8 weeks. If the band does not progress or is negative, it is reported as negative; if it meets the HIV positive diagnostic criteria, it is reported as positive, and if it does not meet the positive criteria, it can be decided whether to follow up. Those who have been tested positive for HIV1 / 2 antibody will issue a confirmation report of HIV1 / 2 antibody positive, and do a good job of consultation, confidentiality and reporting in accordance with regulations.

Antigen detection: mainly detects the P24 antigen core protein of HIV1. In the early and late stages of infection, the P24 antigen appears in free form and in most cases in the form of an antigen-antibody complex. P24 is usually detected within 1-2 weeks after infection and decreases with the production of P24 antibodies. It usually lasts for 0.5-5 months, and if it persists or reappears, it indicates a poor prognosis.

2. Viral load determination

Commonly used methods include reverse transcription PCR (RT-PCR), nucleic acid sequence-dependent amplification (NASBANuclisens), branched DNA signal amplification system (bDNA), and real-time PCR (realtime PCR). The clinical significance of viral load measurement includes predicting the course of the disease, providing a basis for starting antiviral therapy, assessing the effect of treatment, guiding the adjustment of treatment plans, and reference indicators for early diagnosis of HIV infection. The diagnosis of HIV infection in infants and young children under 18 months of age can use nucleic acid detection methods, and the positive results of two nucleic acid tests are used as a reference for diagnosis. After 18 months of age, they can be confirmed by antibody testing. The HIV viral load test results are below the lower limit of detection. The results of this experiment are reported below the lower limit of detection. They are found in individuals who are not infected with HIV, who have received successful antiviral therapy, or who are themselves able to effectively inhibit viral replication. HIV viral load test results above the lower detection limit can be used as auxiliary indicators for the diagnosis of HIV infection, but cannot be used alone for the diagnosis of HIV infection. Recommended viral load testing frequency: For patients who have received antiviral therapy for more than 6 months and the virus is continuously inhibited, it can be tested every 6 months. The frequency of HAART detection within 6 months or when viral load suppression is not ideal or when treatment regimens need to be adjusted needs to be determined by the clinician based on the patient's specific situation. If conditions permit, it is recommended that untreated asymptomatic HIV-infected persons be tested once a year, and tested every 4 to 8 weeks before the initial HAART treatment or adjustment of the treatment plan, or at the beginning of the initial treatment or adjustment of the treatment plan. After the viral load is lower than the lower detection limit, the test is performed every 3 to 4 months. For patients with good compliance, continuous virus suppression for more than 2 to 3 years, and stable clinical and immunological status, the test can be performed every 6 months. .

3.CD4 + T lymphocyte detection

After HIV infection in humans, CD4 + T lymphocytes progressively decrease, the ratio of CD4 + / CD8 + T cells is inverted, and cellular immune function is impaired. If HAART is performed, CD4 + T lymphocytes can be increased to varying degrees at different stages of the disease course. The current commonly used method for detecting CD4 + T lymphocyte subsets is flow cytometry, which can directly obtain the absolute value of the number of CD4 + T lymphocytes, or convert it to the absolute number of CD4 + T lymphocytes after counting by WBC classification. The clinical significance of CD4 + T lymphocyte count is to understand the body's immune status and disease progression, determine the stage of the disease and the timing of treatment, determine the effect of treatment and the clinical complications of HIV-infected patients. The detection interval of CD4 + T lymphocyte count needs to be determined by the clinician according to the specific situation of the patient. It is recommended that HIV asymptomatic infection with CD4 + T lymphocyte number> 350 / L be detected every 6 months; for Patients who have received antiretroviral therapy are tested every 3 months during the first year of treatment. Patients with stable disease for more than 1 year may be tested every six months.

4. HIV genotype resistance test

There are genotypes and phenotypes for resistance detection. At present, genotype detection is mostly used at home and abroad. HIV genotypic resistance testing is recommended when the viral load of antiviral therapy is unsatisfactory or when antiviral therapy fails and the treatment plan needs to be changed; if conditions permit, it is best to perform resistance testing before antiviral therapy. In order to choose the right antiviral drug, get the best antiviral effect. For those who fail antiviral treatment, resistance testing must be performed when the viral load is> 1000 copies / ML and antiviral drugs have not been discontinued. If the drug has been discontinued, genotypic resistance testing must be performed within 4 weeks of discontinuation. HIV resistance in HIV genotype testing indicates that the virus in the infected person may be drug resistant. At the same time, it needs to be closely integrated with the clinic and fully consider factors such as compliance, tolerance to the drug, and metabolic absorption of the drug. . Changing the antiviral regimen requires the guidance of an experienced physician. HIV resistance is negative, indicating that the sample did not detect resistance through genotypic resistance testing, but it is not certain that the infected person does not have drug resistance.

5. Virus isolation

The commonly used method is the co-culture method, that is, mononuclear cells are separated from normal human peripheral blood, stimulated and cultured with PHA, and then mononuclear cells are added to the patient. Currently it is only used for experimental research and is not used as a diagnostic indicator.

Detection of HIVRNA and P24 antigens can shorten the "window period" of antibodies and help early diagnosis of HIV infection in newborns.