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Viral Load Measurement

A viral load test measures how much human immunodeficiency virus (HIV) is in the blood. Viral load is first measured when you are diagnosed with HIV infection. This initial measurement serves as the baseline, and future viral load measurements will be compared with the baseline. Since viral load can vary from day to day, the trend over time is used to determine if the infection is getting worse. If your viral load shows a steady increase over several measurements, it means the infection is getting worse. If the trend in viral load decreases over several measurements, it means that the infection is being suppressed.

The viral load is measured using one of three different types of tests:

  • Reverse-transcriptase polymerase chain reaction (RT-PCR) test
  • Branched DNA (bDNA) test
  • Nucleic acid sequence-based amplification (NASBA) test

These tests measure the amount of the genetic material (RNA) of HIV in the blood. But each test reports the results differently, so it is important to use the same test over time.

Why It Is Done

A viral load measurement test is done to:

  • Monitor changes in the HIV infection.
  • Guide treatment choices.
  • Monitor how well treatment is working.

You and your doctor may set up a different schedule for the test, but the most common schedule is the following:

  • If you are not receiving antiretroviral therapy (ART), your viral load should be measured every 3 to 4 months.
  • If you are receiving antiretroviral therapy:
    • A viral load measurement is taken before you start treatment. This is your baseline measurement.
    • Another viral load measurement is taken 4 to 8 weeks after you start treatment to determine your response to the medicines. When you start treatment or switch to new medicines, some decrease in your viral load is expected.
    • If the expected decrease in viral load occurs and your CD4+ cell count remains stable, your viral load will be measured every 3 to 6 months. The CD4+ count monitors how well your immune system is working.

Your doctor may consider your viral load measurement along with your CD4+ count to decide when to start antiretroviral therapy.

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WebMD Medical Reference from Healthwise

Last Updated: October 22, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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