CD4 Lymphocyte Monitoring

Description

Monitoring lymphocyte counts in a patient with HIV infection is one way to assess the degree of immunosuppression and the risk of developing opportunistic infections.

For several years after exposure to human immunodeficiency virus (HIV), an infected person will typically have either no symptoms or only minor ones such as chronically swollen lymph nodes. However, despite the absence of noticeable symptoms, HIV may be silently causing damage.

HIV infects and kills certain white blood cells called CD4 lymphocytes, reducing their number. The number of CD4 cells usually declines over time in an HIV-infected person. CD4 lymphocytes act as the 'on switch' for part of the immune system, so as the number of CD4 cells drops, damage to the immune system may progress.

Over time, individuals become increasingly susceptible to infections caused by organisms that are usually controlled by people with adequate immune systems. Those infections are called opportunistic infections.

Years after infection, HIV-infected people may develop symptoms such as night sweats, chronic diarrhea, fatigue, fever, and various skin problems. These symptoms vary in severity for each individual. If the individual receives no treatment and further immune impairment occurs, the body becomes susceptible to life-threatening complications.

CD4 Count as a Prognostic Marker

Several different measures can be obtained from a set of blood tests called lymphocyte subset studies: absolute CD4 cell count, absolute CD8 cell count, CD4: CD8 ratio, and the CD4 lymphocyte percentage (that is, the percent of all lymphocytes that are CD4 cells).

The absolute CD4 lymphocyte count is the most widely used predictor of HIV progression. Risk of progression to an AIDS opportunistic infection or malignancy is high with a CD4 count less than 200 cells/microliter.

The CD4 lymphocyte percentage may be more reliable than the CD4 count. The risk of progression to an AIDS opportunistic infection or malignancy is high with a percentage less than 20 percent.

One test by itself cannot determine a course of treatment, but the absolute CD4 lymphocyte count may help indicate which opportunistic infections are likely for that level of immunosuppression. In other words, certain infections are more likely to occur at a given CD4 lymphocyte count.

While the CD4 count measures immune dysfunction, it does not provide a measure of how actively HIV is replicating in the body. That information is provided by HIV viral load tests. Viral load tests correlate with disease progression and the response to antiretroviral medications.

Frequency of Testing

Patients whose CD4 counts are substantially above the threshold for initiation of antiviral therapy (500 cells per microliter) should have counts performed every 6 months.

Patients who have CD4 counts near or below 500 cells per microliter should have counts performed every 3 months.

No single CD4 count can be considered definitive; it is the trend over time that is significant.

Test Anxiety

Regular monitoring with CD4 cell counts or other tests raises the same psychological issues as HIV antibody testing. In order to provide better care for you, it is important to monitor your immune system repeatedly to gauge how well your body is fighting the virus. Most people adapt to the anxiety of the test over time, but counseling is always available to help you deal with your anxiety or fear.

Questions to Ask Your Doctor

What is the CD4 count?

Has the count dropped since it was last taken?

How accurate is the count?

At what level should treatment begin?

How can the symptoms be controlled?

What preventive measures should be taken?

When should the count be repeated?

Is HIV counseling available?