Written By: Satata Karmakar | Published : December 18, 2023 6:57 PM IST
Medically Verified By:
HIV tests are broadly categorized into screening, confirmation, or treatment monitoring. All tests for HIV screening and confirmation of diagnosis should include pretest counseling before performing the tests and post-test counseling before disclosing the results. It may be necessary to refer the patient to appropriate services such as HIV specialists and Integrated Counseling and Testing Centers (ICTC) following NACO guidelines.
We spoke to Dr. Niranjan Patil, AVP, and Scientific Business Head - Infectious Diseases, Microbiology & Molecular Biology- Head & Biosafety officer, Metropolis Healthcare Limited, to understand more about HIV screening and different ways in which this condition can be managed.
In India, HIV screening is conducted following the NACO guidelines for HIV testing. Serological tests, such as HIV1 and 2 antibody tests, can be performed. For individuals aged over 18 years who are clinically asymptomatic, the sample should react to HIV antibodies with three different kits (Strategy III) as per NACO guidelines. Antibody-based tests can take various forms, such as ELISA, CMIA, CLIA, ELFA, lateral flow immunochromatography-based rapid tests, immunofiltration, etc.
Currently, 4th generation assays based on antigen-antibody interactions can be performed, reducing the window period for detection. The window period for antibody-based tests is the time gap between the entry of the HIV virus into the human body and the appearance of detectable antibodies in human serum or plasma samples. This period may vary from 6 weeks to 6 months from person to person, depending on various factors. During the window period, HIV antibody tests may yield false-negative or non-reactive results. HIV antigen-based or HIV PCR-based tests may be recommended for HIV diagnosis during this window period for antibody-based tests.
For newborn infants and children under 18 months of age, maternally acquired antibodies may interfere with antibody-based serological screening tests for HIV. It is recommended to perform nucleic acid-based qualitative tests such as HIV1 proviral DNA PCR, HIV2 RNA PCR, or HIV p24 antigen tests. NACO recommends the use of a dried blood sample to perform DNA PCR tests between 6 weeks to 18 months of age for the diagnosis of HIV in infants.
An HIV 1 and 2 western blot test may be performed, which looks for various proteins of HIV1 and 2. However, it has a longer window period of detection compared to the screening tests and is recommended to be performed for confirmation of the screening results obtained from the antibody-based tests.
Alternatively, HIV testing can be conducted using nucleic acid-based tests such as HIV1 RNA PCR and HIV2 RNA PCR.
HIV tests for treatment monitoring
For known HIV-positive patients who are consuming HIV anti-retroviral agents, viral load tests such as HIV-1 and HIV-2 quantitative viral load tests, which look for HIV RNA viral copies, are used to monitor the response to treatment. These viral load-based tests may be performed at 6-month intervals to assess prognosis. Additionally, tests such as CD4 counts may be used as an additional parameter to monitor the response to anti-viral treatment.
Apart from these, there are tests meant for the detection of resistance to anti-retroviral agents referred to as HIV drug resistance tests, which may be genotypic or phenotypic. Generally, HIV genotypic tests involve DNA/RNA sequencing, which includes performing PCR followed by sequencing of the nucleic acid. This is followed by comparing the sequence obtained with a standard database using sophisticated software algorithms. These HIV drug resistance tests help the HIV specialist doctor choose and alter anti-HIV medications during the course of treatment for an individual patient.
Metropolis has been a pioneer in HIV testing in the private diagnostics sector for more than three and a half decades now and has been an active partner with NACO and the Government of India for HIV viral load testing.
