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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. 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 spread through contact with the body fluids or blood of someone with the virus. It’s transmitted through sex; by sharing needles, syringes, or other equipment; 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 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, he or she is 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.

Blood Tests

The easiest way to diagnose HIV infection is by testing a person’s blood or saliva for antibodies to the virus. The immune system produces antibodies when it detects harmful substances, such as viruses or bacteria. It usually takes about 12 weeks after infection for the body to develop HIV antibodies, but it can take up to six months after infection for an HIV test to have a positive result.

If a doctor suspects a person has an acute HIV infection, meaning the person has recently come into contact with the virus, he or she may order a blood test to check for HIV antigens, which are proteins produced immediately after infection. This test can help the doctor to confirm a diagnosis before an HIV antibody test would show a positive result.

An early diagnosis allows people to begin treatment immediately and helps them take extra precautions to prevent spreading HIV to others.

If a person tests positive for HIV infection, a doctor schedules a follow-up meeting 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 diseases, 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, decide when to start treatment, 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 he or she has no symptoms.

Our Research and Education in HIV Infection and AIDS

Learn more about our research and professional education opportunities.