CD4 and CD8/Viral Load

Posted by Agatha / on 06/17/2009 / 0 Comments

Also known as: T4 count, T-helper cells, T-suppressor cells, Cytotoxic T-cells
Formal name: CD4 lymphocyte count, CD8 lymphocyte count, CD4/CD8 ratio, CD4 percent
Related tests: HIV antibody, p24 antigen test, HIV viral load, HIV genotypic resistance testing, HIV phenotypic resistance testing

How is it used?

If you have been diagnosed with HIV, a CD4 test by itself, a CD4 percent, or a CD4/CD8 ratio is used to help evaluate and track the progression of HIV infection and disease. CD4 cells are the main target of HIV, and the number of CD4 cells will decrease as HIV progresses. Since CD4 cells are usually destroyed more rapidly than other types of lymphocytes and because absolute counts can vary from day to day, it is sometimes useful to look at the number of CD4 cells compared to other types of lymphocytes. Sometimes a CD4 cell count is compared to the total lymphocyte count, and the result is expressed as a percentage, or a CD4 cell count may be compared to a CD8 cell count, and the result is expressed as a ratio.

The CD4 count, CD4 percent, or a CD4/CD8 ratio can tell your doctor how strong your immune system is and can help predict the risk of complications and debilitating infections. These tests are most useful when they are compared with results obtained from earlier tests. They are used in combination with the HIV viral load test, which measures the level of HIV in the blood, to determine the progression and outlook of HIV disease and to monitor the effectiveness of Sometimes, these tests may be used to help diagnose or monitor other conditions such as lymphoma, organ transplantation, and DiGeorge syndrome (see FAQ #4).treatment.

When is it ordered?

A CD4 count, or sometimes a CD4 percent or CD4/CD8 ratio, is ordered with a viral load test when you are first diagnosed with HIV as part of a baseline measurement. The tests should be repeated about two to eight weeks after starting or changing anti-HIV therapy. If treatment is maintained, they should be performed about every three to four months thereafter

 What does the test result mean?
NOTE: This test has no single number that identifies an abnormal result. Your lab report (see a sample report) should include a range of numbers (reference range) that identifies what is expected for you based on your age, sex, and the method used in that laboratory. You can find more information about expected results at Reference Ranges and What They Mean. Lab Tests Online strongly recommends that you discuss the meaning of your test results with your doctor.

A CD4 count may be interpreted as an absolute level, as a ratio to CD8, or as a percent of total lymphocytes. In this section, we use CD4 count to refer to any of these ways of expressing it. In general, the CD4 count goes down as HIV disease progresses. Any single CD4 count value may differ from the last one even though your health status has not changed. Your doctor will take several CD4 test results into account rather than a single value and will evaluate the pattern of CD4 counts over time.

If your CD4 count declines over several months, your doctor may recommend beginning or changing anti-retroviral treatment and/or starting prophylactic treatment for opportunistic infections such as Pnmocystis pneumonia (PCP) or Mycobacterum avium infection. Your CD4 count should increase or stabilize in response to effective combination anti-HIV therapy.

According to public health guidelines, preventive therapy should be started when an HIV-positive person who has no symptoms registers a CD4 count under 200 cells per cubic millimeter of blood. Some physicians will opt to consider treatment earlier, at 350 cells/mm3. The Centers for Disease Control and Prevention considers HIV-infected persons who have CD4 counts below 200 cells/mm3 to have AIDS, regardless of whether they have any signs or symptoms.

Is there anything else I should know?

The CD4 count tends to be lower in the morning and higher in the evening. Acute illnesses, such as pneumonia, influenza, or herpes simplex virus infection, can cause the CD4 count to decline temporarily. Cancer chemotherapy can dramatically lower the CD4 count.

The CD4 count does not always reflect how someone with HIV disease feels and functions. For example, some people with higher counts are ill and have frequent complications, and some people with lower CD4 counts have few medical complications and function well.


This article was last reviewed on March 28, 2009.
This page was last modified on April 8, 2009.

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What Are CD4 Cells?

CD4 cells help to organize your body's defenses against disease. Doctors can take a sample of your blood and count the number of CD4 cells. Healthy adults and teenagers usually have a CD4 count of at least 800 cells per CUBIC MILLIMETER of blood (a cubic millimeter is a very small amount, roughly one small drop).

What Does HIV Do to CD4 Counts?

HIV attacks CD4 cells, and as time goes by people with HIV often see their CD4 counts drop. The lower your CD4 count, the greater your chances of getting a number of very serious diseases. When your CD4 count is below 200, the risk of illness becomes severe.

I've Heard That You Can Have a Low CD4 Count and Still Be Healthy. Is That True?

While there have been a few medical reports of people who seemed healthy even though they had very low CD4 counts, these cases are rare. Research overwhelmingly shows that people with low CD4 counts are much more likely to get sick than people who have a normal amount of CD4 cells.

The AIDS denialists who claim that CD4 counts are meaningless often point to a study of AIDS patients called the Concorde study, in which people who had a small increase in CD4 counts did not live longer than those whose CD4 counts stayed the same. But that study was done nearly 10 years ago, before modern combination therapy, and the CD4 increases were very small. Newer studies with more potent treatments show that a big boost in CD4 cells almost always lowers the risk of getting seriously ill.

For example, the deadly pneumonia called PCP occurs much more often in people with very low CD4 counts. In one study with over 1,000 patients, almost everyone who got PCP had a CD4 count below 200. Study after study has shown the same thing: The lower your CD4 count, the greater your chance of getting PCP or other serious infections.

The AIDS denialists leave out these important facts.

Why Are Viral Load Tests Used?

CD4 counts give you and your doctor a good idea of how much damage HIV has done to your immune system. But you also need to know how fast that damage is happening. Viral load tests, which tell the doctor how much HIV is in your blood, are a very important clue to how quickly HIV is doing harm.

These tests go by several different names, like PCR (polymerase chain reaction) or bDNA (branched DNA), but they all work roughly the same way. They count HIV's genetic material -- the building blocks of the virus.

What Does Viral Load Tell Us?

People with a high viral load are much more likely to get sick or die of AIDS than people with a low viral load.

The AIDS denialists sometimes suggest reasons why these tests might give a wrong answer. They point to a few old reports, from when viral load tests were new and still experimental, as evidence that they don't work. But there is a huge pile of newer evidence showing that viral load tests work extremely well. Many studies have shown that people with high viral loads are more likely to get sick or die from AIDS-related illnesses than people whose viral load is lower.

For example, one very important study has followed thousands of gay men since 1984. A few years ago researchers did viral load tests on the very earliest blood samples from that study and then looked at how many of those patients were still alive. The men with the highest viral loads were 77 times more likely to have died of AIDS than those with the lowest viral loads. Other studies in the U.S. and Europe have shown the same thing: A higher viral load almost always means a higher risk of sickness and death.

What Happens When Treatment Reduces My Viral Load?

Studies have shown that when treatment reduces your viral load, it also reduces your chance of getting an AIDS-related infection or dying. Recently, a group of expert scientists reviewed 18 studies of anti-HIV drugs, which involved over 5,000 patients. Over and over again they found the same thing: The more viral load was reduced, the healthier the patients stayed.

The Bottom Line

No medical test is perfect, and mistakes or misunderstandings sometimes happen. You should always go over your test results carefully with your doctor to make sure you understand them.

But the people who claim that viral load and CD4 tests are useless are not telling the truth. These tests give you and your doctor important information that can help you make the best treatment choices.

ISSN # 1052-4207

Copyright 2001 by John S. James. Permission granted for noncommercial reproduction, provided that our address and phone number are included if more than short quotations are used.

Back to the AIDS Treatment News May 11, 2001 contents page.

This article is part of's archive. Because it contains information that may no longer be accurate, this article should only be considered a historical document. 

CD4 & viral load
May 13, 2009

I am on ART for almost 5 years. I have done couple of viral load testing. The first one was done on April 2007 and the last one was done on Janaury, 2009 and the result for both the testing came out with less than detectable limit. On the other hand CD4 count is still low below 400 though I have been noticing it gradually increase. When I started ARV my CD4 count was only 5 and at that time I was diagonise with PCP. I am still healthy since the initiation of ART and haven't ecounter any major illness so far. My CD4 count is suppose to increase because my viral load is still remain less than dectable limit since last two years. I heard that the higher the CD4 count the lower the viral load but the comparision is seems to be opposite in my case. Do you think that this is a problem or need to consult with a physician?

Response from Dr. Henry

Recovery of CD4 cells is highly variable with a significant % (perhaps 10-15%) having a suboptimal increase despite good viral suppression (called discordant response). Antiretroviral therapy only suppresses HIV levels-CD4 recovery depends on viral suppression and other key factors including thymus status, genetics, level of immune activation and others. If your HIV levels are fully suppressed then the ART is doing its job-there is little data that switching meds or adding HIV meds will predictably hasten CD4 recovery (which in some cases will slowly climb over the years if patient). IL-2 has been looked at as a CD4 booster and was recently shown to provide no clinical benefit despite an increase in the measured CD4 count. KH



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