Blood work:
A complete guide for monitoring HIV
May 2007 View PDF En
español
Lymphocyte subsets:
CD4 cells and viral load
Specific tests for people with HIV
Lymphocytes are a type of white blood cell. Routine counts provide
information about the state of your immune health. Three types of
lymphocytes are routinely tested: B cells, T cells (CD4+ and CD8+
cells) and NK cells (natural killer cells). B cells are involved
in the production of antibodies. They also deal with infections
that are outside cells. CD8+ cells deal with infections that are
inside cells. CD4+ cells “help” B cells and CD8+ cells
do their jobs.
CD4+ and CD8+ cell counts
CD4+ cells help control the activity of other cells. HIV infects
CD4+ cells and makes more copies of itself. Over time, HIV causes
a decline in the number of these cells. So getting routine CD4+
cell counts done is the main way to keep track of your immune health.
In HIV-negative people, normal CD4+ cell counts
are 500–1,500/mm3 of blood. Normal CD8+ cell counts are 300–800/mm3.
In general, people have 2-to-1 ratios of CD4+ to CD8+ cells. So
for every two CD4+ cells, an HIV-negative person has one CD8+ cell
in their blood. However, in most people living with HIV who are
not on anti-HIV therapy, it’s common for the normal CD4+/CD8+
ratio to be reversed.
It’s also helpful to look at the percentages
of CD4+ and CD8+ cells in a blood sample. The CD4+ percentage is
the percentage of CD4+ cells in the total lymphocyte count. The
normal range is 28–58%. Another helpful measure is the CD4+/CD8+
ratio.
CD4+ cell counts are also the best guide for when
to start preventive therapy for opportunistic infections, or OIs.
CD4+ cell counts may vary due to many factors, such as the time
of day, an active infection, stress or lab variations. Therefore,
it’s important to look at your CD4+ cell count trends over
time and not be alarmed by any one test result. CD4+ cell counts
also are used to make decisions on when to start or change therapy.
What do CD4+ cells counts mean?
Above 500 CD4+ cells
- No unusual conditions likely. Emphasize good health
habits and health care maintenance, including vaccines and nutrition.
200–500 CD4+ cells
- Increased risk for shingles
(zoster), thrush (candida),
skin infections, bacterial
sinus and lung infections, and TB.
- Life-threatening OIs (such as PCP,
MAC and CMV)
are rare.
- NoAnti-HIV therapy is generally recommended when CD4+ cell counts
are in the 200 to 350 range.
50–200 CD4+ cells
- Increased risk for PCP and other opportunistic infections.
- Preventive treatment for PCP is indicated.
- If counts are below 100, consider preventive treatment for MAC,
CMV and invasive fungal infections.
Below 50 CD4+ cells
- Increased risk for opportunistic infections, including
MAC and CMV.
- Continue preventive medication.
Viral load tests
Viral load tests measure the amount of HIV in about a teaspoon of
blood. They are important for monitoring HIV disease and how well
therapy is working. When HIV levels decrease or stay low and stable
over time, it’s a sign that potent anti-HIV therapy is working.
When the levels increase, it’s often a sign that a regimen
has stopped working.
At first, two tests should be taken about 2–4
weeks apart to establish a baseline level. After that, viral load
tests should be done every 3–4 months. People should generally
avoid having viral load tests done during an active infection (like
a cold), after a vaccination (like flu) or during flare-ups of infections
(like a cold sore). These can all cause HIV levels to briefly increase.
They usually return to normal within a few weeks after a vaccination
or the end of the infection.
A viral load test should also be done 3–4
weeks after starting or changing therapies. To get accurate results
and trends over time, it’s wise to get the same brand of test
done each time at the same lab. The trend of viral loads over time
is the most important and not an individual result.
Low, stable and decreasing viral load is considered
a good thing. High or increasing levels call for attention as it
may point to the failure of a regimen. Viral load below 10,000 copies
is generally considered “low.” Viral load above 100,000
copies is generally considered “high.”
Women may have a “naturally” lower viral
load than men, especially in early HIV infection. Therefore, women
should be aware that a viral load above 30,000 or even 60,000 might
indicate a “high” viral load for them.
People with “undetectable” viral load
should remember that it does not mean that their HIV is gone. HIV
may actually be there, but just in too small of a quantity to detect.
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