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 highly active antiretroviral therapy (HAART), 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.
How To Prepare
You do not need to do anything before you have this test.
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Apply a gauze pad or cotton ball over the needle site as the needle is removed.
- Apply pressure to the site and then a bandage.
How It Feels
You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. But many people do not feel any pain (or have only minor discomfort) after the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your veins, and your sensitivity to pain.
There is very little risk of complications from having blood drawn from a vein.
- You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
- In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
- Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.
A viral load test measures how much human immunodeficiency virus (HIV) is in the blood. The results can take up to 2 weeks.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab and depend upon which testing method is used (RT-PCR, bDNA, NASBA). Your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Viral load results are reported as the number of HIV copies in a milliliter (copies/mL) of blood. Each virus is called a "copy," because HIV reproduces by making copies of itself (replicating).
HIV is not detected in the blood.
HIV is detected in the blood. Your doctor will compare your current measurement with previous values.
If your viral load increases, it means the infection is getting worse. If the viral load drops, it means that the infection is being suppressed.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include having another infection, such as pneumonia, or certain immunizations, such as a flu shot.
What To Think About
- The results from the different methods (RT-PCR, bDNA, NASBA) to measure viral load are not interchangeable. This makes it important to use the same method of measuring each time.
- An undetectable viral load result does not mean that you no longer have HIV in your blood. It simply means that the amount of HIV in the blood was too low for the test to detect. HIV still can be passed to another person even when the viral load cannot be detected.
- The viral load test is not used routinely to diagnose HIV. The HIV antibody test is used for this purpose. For more information, see the topic Human Immunodeficiency Virus (HIV) Test.
- The viral load test is more accurate than a CD4+ count to evaluate the activity of HIV. The CD4+ count measures how well your immune system is working and may be used to determine when to start antiretroviral therapy. The viral load test is used to determine the response to antiretroviral therapy. No HIV should be detected in the blood of people whose treatment is successful. For more information about the CD4+ count, see the topic CD4+ Count.
Other Works Consulted
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
|Primary Medical Reviewer||E. Gregory Thompson, MD - Internal Medicine|
|Specialist Medical Reviewer||Peter Shalit, MD, PhD - Internal Medicine|
|Last Revised||April 8, 2010|