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.
viral load is measured using one of three different types of tests:
Reverse-transcriptase polymerase chain reaction
Branched DNA (bDNA) test
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
Monitor changes in the HIV
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:
A viral load measurement is taken before
you start treatment. This is your baseline measurement.
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
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
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
Put the needle into the vein. More than one needle stick
may be needed.
Attach a tube to the needle to fill it with
Remove the band from your arm when enough blood is
Apply a gauze pad or cotton ball over the needle site as
the needle is removed.
Apply pressure to the site and then a
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
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.
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.
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
HIV is not detected in the
HIV is detected in the blood.
Your doctor will compare your current measurement with previous
If your viral load increases, it means the infection is
getting worse. If the viral load drops, it means that the infection is being
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
infection, such as
Having gotten a recent vaccine, such as a flu vaccine.
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.
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 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. To learn more about
the CD4+ count, see the topic
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.
How this information was developed to help you make better health decisions.