Interpreting CD4,when to use CD4 %..USER MANUAL

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How to Interpret CD4 and CD8 Test results

Several laboratory tests are routinely performed as part of standard
HIV patient management. These include tests related to drug toxicity,
opportunistic infections, HIV viral status (viral load), and immune
competency (CD4).
The CD4 test measures the concentration of CD4 positive (CD4+) T cells in the body. CD4+ T cells or T-helper cells are key components of the immune system that help it identify bacteria and viruses. In a healthy individual, the normal concentration of CD4+ T cells can range from 500 to 1400 cells/mm3.1
One of the hallmarks of HIV infection is the depletion of CD4+ T
cells. This depletion impairs the body's immune system and allows
opportunistic diseases to cause infections. Simply put, the lower the
concentration of CD4+ T cells, the higher the risk of developing
opportunistic infections. Late-stage HIV infection is defined by a
CD4 count of <200 cells/mm3.
One of the difficulties in interpreting CD4 test results is the
inherent variability of the results.
An individual's CD4 count can vary for numerous reasons other than the status of HIV infection. CD4 counts are influenced by time of day, the season of the year, common infections, surgery, and some drugs including corticosteroids. CD4 counts are usually lowest at midday and highest in the evening.2 Infections and major surgery also decrease CD4 counts.
Corticosteroids can drastically lower CD4 counts. Pregnancy, age,
gender, and stress have only minimal effects on CD4 counts.
In the management of HIV patients, CD4 tests are typically performed
every 2 to 6 months depending on whether or not the patient is on
therapy. Like HIV viral load results, CD4 test results are usually
serially monitored, which means that the current result is compared
to historical results to identify any trends. If a result is
inconsistent with any prior trends, the test should be repeated.3
CD4+ T cell concentrations can be reported in two different ways:
absolute CD4 counts and percent CD4 (%CD4).
Absolute counts are reported as cells per mm3; %CD4, which is the percent of CD4+ T cells in a total white blood cell count, is sometimes used because it varies less than the absolute count.
Table 1 shows the correlation between absolute and percentage counts.
Frequently, there will also be information about CD8+ T cells (T-
suppressor cells) in the CD4 test results.
T-suppressor cells work in conjunction with T-helper cells (CD4+ cells). T-helper cells help the immune system identify bacteria and viruses; T-suppressor cells are involved in stopping the immune response. CD8+ cells are measured at the same time as the CD4+ cells. In healthy adults, a normal CD8 count is between 375 and 1100 cells/mm3. Unlike CD4+ T cells, CD8+ T cells have not been found to correlate with disease outcome.
However, the ratio of CD4+ cells to CD8+ cells (T-helper cells/T-
suppressor cells) may be used as a monitoring tool for immune status
much like absolute CD4 counts are used. The normal ratio of CD4+
cells to CD8+ cells is around 1 to 2 CD4+ T cells to every CD8+ T
cell. Therefore, drops in the CD4/CD8 ratio, CD4 percentage, or
absolute CD4 counts are all indications of a depletion of T-helper
cells in the immune system.
Clinically, the concentration of CD4+ T cells, measured by absolute
CD4+ cell counts, %CD4 cells, or CD4/CD8 ratio, is essential in HIV-
positive patient management. In untreated patients, CD4 counts drop
significantly each year. By contrast, CD4 counts will typically
increase with successful antiretroviral therapy. Counts can increase
as much as 50 cells/mm3 4 to 8 weeks after starting therapy.4
Therefore, the concentration of CD4+ T cells is a critical tool when
making decisions about when to start antiretroviral therapy, and
since depletion of T-helper cells increases the risk of opportunistic
infections, CD4 counts are also needed to make decisions about
therapies to prevent opportunistic infections.5,6
Timothy M Alcorn, PhD is the Executive Director of Molecular
Pathology for Esoterix, Inc.
The CD-4 count in healthy adults ranges from 500 to 1,500 cells per
cubic millimetre of blood. In HIV infected people, it goes down by 60
cells per cubic millimetre of blood per year as HIV progresses. ART
is administered when an HIV-positive person registers a CD-4 count
under 200.