Tests and diagnosis

By Mayo Clinic Staff

HIV is most commonly diagnosed by testing your blood or saliva for antibodies to the virus. Unfortunately, it takes time for your body 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 that checks for HIV antigen, a protein produced by the virus immediately after infection, can confirm a diagnosis within days of infection. An earlier diagnosis may prompt people to take extra precautions to prevent transmission of the virus to others. There is also increasing evidence that early treatment may be of benefit.

Tests to tailor 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 you have no symptoms, HIV infection progresses to AIDS when your CD4 count dips below 200.
  • Viral load. This test measures the amount of virus in your blood. Studies have shown that people with higher viral loads generally fare more poorly than do those with a lower viral load.
  • Drug resistance. This blood test determines whether the strain of HIV you have will be resistant to certain anti-HIV medications.

Tests for complications

Your doctor might also order lab tests to check for other infections or complications, including:

  • Tuberculosis
  • Hepatitis
  • Toxoplasmosis
  • Sexually transmitted infections
  • Liver or kidney damage
  • Urinary tract infection
May. 20, 2014

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