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Diagnosing HIV Infection & AIDS

Doctors at NYU Langone diagnose human immunodeficiency virus, known as HIV, a chronic viral infection that destroys certain infection-fighting white blood cells. If left untreated, HIV weakens the immune system, so the body is unable to fight infections and disease. When this occurs, HIV infection leads to a chronic, possibly life-threatening illness called acquired immunodeficiency syndrome, or AIDS.

HIV is transmitted through sex; by sharing needles, syringes, or other equipment; through contact with infected blood; or through pregnancy, childbirth, or breastfeeding.

A few weeks to three months after becoming infected with HIV, many people develop intense flu-like symptoms, such as fever, fatigue, and swollen lymph nodes. They may also experience weight loss and night sweats during this initial phase. However, many people who are infected with the virus have no symptoms for 10 years or longer.

After the initial phase of an HIV infection, the disease moves into a period called “clinical latency.” This means the virus is developing but is producing few if any mild symptoms. Even when it causes no symptoms, the virus can be transmitted to others.

As HIV multiplies and destroys certain white blood cells—the CD4 cells, which fight bacteria and viruses—a person may develop symptoms of infection. These might include recurring fever, intense night sweats, and prolonged swelling of lymph glands in the armpits, groin, or neck. Sores in the mouth, anus, or genitals may also occur.

Many of the severe symptoms and illnesses associated with untreated HIV arise from infections that take advantage of the body’s weakened immune system. There are many of these opportunistic infections, which include pneumonia and cryptococcosis, a fungal infection. In addition, cytomegalovirus, a common virus related to the one that causes chickenpox, or nontuberculous mycobacterial infections, a group of lung infections, may occur. People with HIV infection are also at increased risk of osteonecrosis, a bone disorder.

If a person with HIV infection is not treated, they are likely to develop AIDS, though it’s impossible to predict how long that may take. With treatment, people develop AIDS very slowly—or not at all.

To diagnose the condition, NYU Langone doctors begin by performing a physical exam and taking a medical history. Then they confirm the diagnosis based on the results of certain tests.

HIV Testing

The easiest way to diagnose HIV infection is by testing a person’s blood or saliva for evidence of the virus. There are different types of tests to detect HIV infection.

Rapid HIV Tests

There are two types of rapid HIV tests: one that looks for antibodies, which is a sign that your immune system has come into contact with the virus, and one that looks for antibodies as well as antigens, which indicate an active infection.

Rapid HIV antibody tests use a drop of blood from a small fingerstick or saliva from an oral swab. These tests can provide results in as little as 20 minutes, and can be taken at the doctor’s office or at home. A positive result on a rapid HIV test is considered preliminary, and needs to be confirmed by your doctor with a more conclusive blood test. It usually takes about 12 weeks after infection for the body to develop HIV antibodies.

An antibody–antigen test is a fingerstick rapid test that can detect HIV sooner than an antibody-only test. Antigens, which are proteins produced immediately after infection, can usually be detected within 2 to 4 weeks after HIV infection.

To learn more about HIV testing and prevention, please contact our HIV prevention navigator, part of the HIV Prevention Program at the Family Health Centers at NYU Langone. The navigator can help you schedule an in-office HIV test or arrange for an oral swab rapid antibody test to be mailed to your home. Call 718-431-2667 for more information.

Polymerase Chain Reaction Test

If a person had a recent exposure to HIV, or is experiencing symptoms of acute HIV infection such as fever, fatigue, and swollen lymph nodes, a doctor may order a polymerase chain reaction (PCR) test. Unlike antibody and antigen tests that look for the body’s response to HIV, the PCR test detects HIV itself. This test is typically used three days to one month after an exposure. An early diagnosis allows people to begin treatment immediately and helps them take extra precautions to prevent spreading HIV to others.

If a person receives a positive HIV test result, a doctor schedules a follow-up appointment to discuss the results and the next steps for treatment. The doctor may order several additional blood tests to estimate how long the person has been infected and how far the condition has progressed.

A doctor may also use blood tests to screen for complications or other infections, such as other sexually transmitted infections, as well as toxoplasmosis, which is a parasitic infection, or hepatitis, a liver infection.

Viral Load Test

A viral load test measures the amount of HIV in the blood. Knowing the viral load helps a doctor monitor HIV in the blood and determine whether medications are working.

CD4 Count

A CD4 count measures the amount of CD4 cells in a person’s blood. CD4 cells are white blood cells that fight disease and infection. HIV invades CD4 cells, using them to multiply and spread the virus throughout the body. This process also kills the CD4 cells.

A healthy person’s CD4 count can vary from 500 to about 1,500 cells per cubic milliliter of blood. Doctors diagnose AIDS when a person’s CD4 level drops below 200 cells per cubic milliliter of blood—even if there are no symptoms. Appropriate antiretroviral therapy can help people living with HIV to maintain a high CD4 count.

Our Research and Education in HIV Infection and AIDS

Learn more about our research and professional education opportunities.