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What is a CD4 Count?

By Adam Hill
Updated May 16, 2024
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A CD4 count is the measured level of a certain type of protein, which is often present in certain types of white blood cells. CD4 stands for "cluster of differentiation four," and is an important component of the body's ability to produce an immune response to a would-be infection. A CD4 count can also refer to the specific lab work that is done to determine its level, as a routine part of treatment for someone with the humane immunodeficiency virus (HIV), which can lead to acquired immune deficiency syndrome (AIDS).

Whenever a person visits his HIV specialist, a CD4 count will be taken, to determine, at a glance, the condition of his immune system. CD4 is often present in T-cells and other cells which form and coordinate the body's immune system. The HIV virus can take over and use these cells to make copies of itself, which go on to use other immune cells to make other copies. For a while, the body can replace T-cells at a fast enough rate to combat this pattern. With proper treatment, this time period can be greatly extended, but the CD4 count is watched vigilantly as an indicator of the progression of HIV.

As HIV progresses, a person's CD4 count will go lower and lower, indicating that the presence of the virus is stronger. The results of the count are usually expressed in the number of cells per microliter of blood, an amount which is roughly the size of a pea. A person who is free of HIV will normally have upwards of 750 T-cells in this amount of blood. Someone who is HIV positive is considered to have a normal CD4 count if this number is around 500 in the same amount of blood. Should this number be lowered below 200, this will be an indication of serious immune damage.

A count below 200 is the threshold beyond which a person is medically defined as having AIDS, as opposed to just being infected with HIV. The CD4 count number, while important, also fluctuates considerably. For instance, a person's CD4 is usually higher in the evening than in the morning, and can be affected by the presence of an acute illness like the flu. Simple stress and fatigue can also affect the results. Thus, the CD4 count is useful over time to determine a pattern of immune system health, but the variability of this number over the course of even a single day should be taken into account when interpreting these test results.

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Discussion Comments
By anon285287 — On Aug 15, 2012

What AIDS epidemic? Look around you. Is it like the Black Death where people in every second house are dying? Think about it!

By pastanaga — On Jan 15, 2012

@KoiwiGal - We have the power to stop a lot of diseases right now. Even malaria wouldn't survive long if there was a real concerted effort of the kind that eliminated it from areas like Florida.

It is sad that AIDS keeps going even when we have the power to stop it, but honestly we've had that power since it was discovered.

Condoms are easy and cheap and more ubiquitous than the kind of health care checks you're thinking of.

But they require consistent personal responsibility and no where in the world is that a universal trait.

Once they come up with a real vaccine, then we will have a chance to overcome human nature and get rid of AIDS. No more need to have CD4 counts, HIV will become something rare and unusual.

Before that, I'm afraid the tragedy will continue.

By KoiwiGal — On Jan 15, 2012

@bythewell - AIDS is no longer a death sentence if you happen to be wealthy enough to afford health insurance or health care.

The necessary medications are still far beyond the reach of most people in developing nations, and even some people in wealthier nations.

For those people, it is still a death sentence, and even worse, for many people without access to or knowledge of birth control it's a death sentence for their children.

The thing that kills me about this is that they have a way to stop the AIDS epidemic in its tracks, right now. There is a type of medication available which can make the amount of "shedding" so negligible that it's virtually impossible to pass on the disease.

If they had mandatory AIDS tests and made everyone who has it go on this medication, AIDS could be eliminated in a matter of decades.

This is a disease that has killed millions, with millions more infected. Some countries have an infection rate of 5% or more. And these are the kind of people who aren't going to be able to afford a CD4 count. They just get sicker until one day they die.

That we have the power to stop it right now but we don't is very sad to me.

By bythewell — On Jan 14, 2012

Finally it seems like researchers are starting to make inroads on the AIDS epidemic. There are several promising vaccines that are close to being released. Unfortunately, I don't think any of them are 100% yet, but anything is better than nothing when you consider how many people are suffering around the world from AIDS.

Not to mention the fact that anyone who has access to modern medicine now has less to worry about the CD4 cell count. They have regular tests to ensure it is at the correct level, but generally doctors have enough medicines to keep those levels high.

AIDS is no longer a death sentence. Which is not to say that it is a disease anyone would ever welcome.

So always remember to be safe with your sexual activity. Even if it is no longer strictly deadly, AIDS is still a terrible disease.

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