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Re: Difference between CD4 Count and CD4 Percentage

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How to Interpret CD4 and CD8 Test results

Re: /message/8740

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

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.

Dr Diwakar Tejaswi

Patna, India

e-mail: <diwakartejaswi@...>



ce J. T-cell subsets in health, infectious disease, and

idiopathic CD4+ T lymphocytopenia. Ann Intern Med 1993; 119;55†" 62.

Malone JL, Simms TE, Gray GC, et al. Sources of variability in

repeated T-helper lymphocyte counts from human immunodeficiency virus

type 1†" infected patients: total lymphocyte count fluctuations and

diurnal cycle are important. J Acquir Immune Defic Syndr 1990: 3

(2):144†" 151.

Bartlett J. 2003 Medical Management of HIV Infection. s Hopkins

Press, 2003: p.18.

Blankson JN, Gallant JE, Quinn TC, et al. Loss of HIV-1-specific

immunity during treatment interruption in two chronically infected

patients. JAMA 2002, 288(2); 62†" 64.

Mellors JW, Munoz A, Giorgi JV, et al. Plasma viral load and CD4+

lymphocytes as prognostic markers of HIV-1 infection. Ann Intern Med

1997, 126(12); 946†" 954.

Egger M, May M, Chene G, et al. Prognosis of HIV-1-infected patients

starting highly active antiretroviral therapy: a collaborative

analysis of prospective studies. Lancet

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Dear Forum,

Re: /message/8740

This is a valid question from an grass root level worker.

knowing this at grass root level is much important.

In adults we usally talk about cd4 count and usally below 200 is

defined as AIDS or advanced stage when the oppurtunistic infections

will occur.

But for children, usally the counts will be very high and 3 or 4

times higher than the adults. this will come to adult range of cd4 by

5-6 years mostly.

If the cd4 count says 500 in 2 years, it still means it it equal to

200 in adults. To overcome this confusion, cd4 percentage is a good

marker. normal is above 25% severe immunodeificeny is <15%.

So is children, it will be based on cd4% and in adults on cd4 count


Dr. Mari Raj,

ART MO, Tirunelveli, Tamilnadu.

e-mail: <marirajdr@...>

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