Diagnostic Methods in HIV Infection

HIV (Human Immunodeficiency Virus) is an infectious agent that enters human immune cells, weakens the immune system, and leads to the development of opportunistic infections.

Being HIV positive means that HIV is present in a person’s body. However, this does not mean that the person becomes ill immediately. HIV may remain asymptomatic for many years. With treatment, people living with HIV can lead long and healthy lives.

AIDS (Acquired Immune Deficiency Syndrome) is a clinical condition caused by HIV. It occurs when extensive damage to immune cells allows opportunistic infections to progress and result in severe disease. Bacterial, viral, fungal, or protozoal infections that develop when the immune system is insufficient are referred to as opportunistic infections. With early diagnosis and advances in treatment, people living with HIV can live for many years without progressing to the AIDS stage.

• Everyone between the ages of 15 and 64 (at least once in their lifetime)
• People who have had unprotected sexual intercourse or whose partner’s HIV status is unknown
• People at risk of transmission through blood exposure (exposure to blood and blood products, sharing needles, etc.)
• Pregnant women (to prevent mother-to-child transmission)

People in these groups are advised to undergo HIV testing.

HIV/AIDS infection is diagnosed using laboratory tests specific to the disease.

The appropriate test should be selected according to the time elapsed since exposure.
Risk Assessment — Evaluate the potential exposure and symptoms (fever, sore throat, rash, and swollen lymph nodes).

Note: If you believe you have recently been exposed to HIV, the earliest test that can be performed is an HIV RNA PCR test within 10–14 days. However, for definitive confirmation, an HIV-1 and HIV-2 Antibody Test should be performed after 3 months.

The tests used in the diagnosis of HIV are as follows:

HIV RNA (PCR) — Molecular Tests

The HIV RNA test helps detect HIV at an early stage by directly identifying the genetic material (RNA) of the HIV virus.

During the first 8–10 days after HIV transmission, the virus cannot be detected using currently available tests. This period is referred to as the “Eclipse Phase.”
Molecular methods (PCR);

• Viral RNA can be detected using the PCR method approximately 10 days after transmission, once the Eclipse Phase has ended. Because this test can detect the virus approximately 10 to 14 days after exposure, before antibodies become detectable, it is used for the early diagnosis of HIV.
• It is also effective in confirming inconclusive results obtained from other HIV tests and in monitoring prognosis and treatment in confirmed HIV infection.
• It is used in the diagnosis of acute HIV infection, when the antibody response is insufficient.

Serological Tests — HIV Screening Tests

At all our branches, the 4th-generation HIV DUO ELISA test is performed using a bioMérieux analyzer.

This test detects HIV-1 and HIV-2 antibodies and the HIV-1 p24 antigen.

ELISA tests that detect antibodies specific to HIV-1 and HIV-2, or both antibodies and the HIV-1 p24 antigen, are frequently used in the diagnosis of HIV infection. These tests are classified into generations according to the characteristics of the antigen and/or conjugate used. Today, the use of fourth-generation ELISA tests, referred to as “combo” tests, which can detect HIV-1 and HIV-2 antibodies together with the HIV-1 p24 antigen, is recommended.

Fourth-generation HIV Combo  ELISA tests have higher sensitivity than other test kits and can detect infected individuals at an early stage, at approximately day 17.

During the first eight to ten days after transmission of the virus, known as the Eclipse Phase, there is no serological or virological diagnostic method available for detecting the infection. The end of the Eclipse Phase is indicated by the detection of viral RNA using the PCR method at an average of 10 days after transmission, followed by the detection of the p24 antigen by ELISA 4–10 days later. This period, during which antibodies cannot be detected, is called as acute HIV infection. Infectivity is very high during this period, when the number of viral particles increases rapidly.

Negative Result (HIV Non-Reactive): After all samples have been screened using fourth-generation ELISA tests for the presence of HIV-1 and HIV-2 antibodies and p24 antigen, if there are no clinical findings suggestive of HIV infection and no history of exposure, the result is reported as “HIV non-reactive”. This means that HIV infection has not been detected. However, tests performed during the early period may be misleading; therefore, the test should be repeated in suspected cases.

If clinical findings are present, the test result is reported as “HIV negative” but repeating the test after two to four weeks is recommended. A negative result from a test performed during the early period does not mean that the infection is completely absent from the body. Individuals with suspected infection should repeat the test at the appropriate time, even if the test result is negative.

In the presence of a recent high-risk exposure or signs of acute retroviral syndrome, viral HIV RNA testing should be performed immediately. If positivity is detected by NAT, the result is reported as “HIV-1 positive”; if negative, it is reported as “HIV-1 negative.”

The content on this website is provided for general informational purposes only and should not be considered a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional regarding any medical condition or treatment.

Date Updated: 05.08.2026
Editors: Alev Dülger Dağlı
Contact: [email protected]