Students hold oil lamps beside a symbol of AIDS in Chennai

HIV Testing

How to diagnose HIV/AIDS?

HIV is most commonly diagnosed by testing blood or saliva for the presence of antibodies to the virus. These types of HIV tests aren’t accurate immediately after infection because body takes time to develop these antibodies — usually up to 12 weeks. In rare cases, it can take up to six months for an HIV antibody test to become positive.

A newer type of test checks for HIV antigen, a protein produced by the virus immediately after infection. This test can confirm a diagnosis within days of infection. An earlier  diagnosis help people to take extra precautions to prevent transmission of the virus to others.

Tests to start treatment:

If you receive a diagnosis of HIV/AIDS, several types of tests can help your doctor determine what stage of the disease you have. These tests include:

  • CD4 count. CD4 cells are a type of white blood cell that’s specifically targeted and destroyed by HIV. A healthy person’s CD4 count can vary from 500 to more than 1,000. Even if a person has no symptoms, HIV infection progresses to AIDS when his or her CD4 count becomes less than 200.
  • Viral load. This test measures the amount of virus in your blood. Studies have shown that people with higher viral loads generally have poor prognosis than do those with a lower viral load.
  • Drug resistance. This type of test determines if your strain of HIV is resistant to any anti-HIV medications.

Tests for complications
There are other lab tests to check for other infections or complications, including:

  • Tuberculosis
  • Hepatitis
  • Toxoplasmosis
  • Sexually transmitted diseases
  • Liver or kidney damage
  • Urinary tract infections

What laboratory tests are used to monitor HIV-infected people?

Two blood tests are routinely used to monitor HIV-infected people. One of these tests, which counts the number of CD4 cells, assesses the status of the immune system. The other test, which determines the so-called viral load, directly measures the amount of virus in the blood.

In individuals not infected with HIV, the CD4 count in the blood is normally above 500 cells per mm3 of blood. People generally do not become at risk for HIV-specific complications until their CD4 cells are fewer than 200 cells per mm3. At this level of CD4 cells, the immune system does not function adequately and is considered severely suppressed. A declining number of CD4 cells means that HIV disease is advancing. Thus, a low CD4 cell count signals that the person is at risk for one of the many opportunistic infections. In addition, the actual CD4 cell count indicates which specific therapies should be initiated to prevent those infections.

The viral load actually measures the amount of virus in the blood and may partially predict whether or not the CD4 cells will decline in the coming months. Patients with high viral loads are more likely to experience a decline in CD4 cells and progression of disease than those with lower viral loads. In addition, the viral load is an important tool for monitoring the effectiveness of the therapy and determining when drugs are working or not. Thus, the viral load will decrease within weeks of initiating an effective antiviral regimen. If a combination of drugs is very potent, the number of HIV copies in the blood will decrease by as much as hundredfold, such as from 100,000 to 1,000 copies per mL of blood in the first two weeks and gradually decrease even further during the next 12-24 weeks. The ultimate goal is to get viral loads to below the limits of detection by standard assays, i.e, less than 50 or 75 copies per mL of blood. When viral loads are reduced to these low levels, it is believed that the viral suppression will persist for many years as long as the patient continues to take medication.

Drug-resistance testing also has become a key tool in the management of HIV-infected individuals. Resistance testing is now routinely used in individuals experiencing poor responses to HIV therapy or treatment failure. In general, a poor response to initial treatment would include individuals who fail to experience a decline in viral load of approximately hundred fold in the first two weeks, or a viral load of greater than 500 copies per mL by week 12, or have levels greater than 50 or 75 copies per mL by week 24. Treatment failure would generally be defined as an increase in viral load after an initial decline in a person who is believed to be consistently taking his or her medications. More recent guidelines from the U.S. Department of Health and Human Services (DHHS) and International AIDS Society-USA (IAS-USA) have suggested that resistance testing be performed in individuals who have never been on therapy to determine if they might have acquired HIV that is resistant to drugs.

Leave a Reply

Your email address will not be published. Required fields are marked *