Monitoring Your Immune System and the Virus

Part of A Practical Guide to HAART (Highly Active Anti-retroviral Therapy)

Developing any of the infections that are related to AIDS is a clear sign that the immune system is damaged and no longer able to fully protect you from invading organisms. But instead of waiting until someone becomes ill, lab tests can be used to get an idea of how well the immune system is coping with HIV infection.

The most important thing to know about the tests described below is that it is the trend of your test results over time that is important, not any single reading. Whether it's a CD4+ count or a viral load that concerns you, making a snap judgment or a treatment change based on any single test would be a very bad idea. At the very least, any significant change should be confirmed with a follow-up test. And always, always consider the pattern over the last few tests in your decision-making.

A complete immune panel reports many test results, as listed below (your doctor will not order all of these tests all of the time):

  • the total number of white blood cells (WBC);

  • the total number of lymphocytes (T cells, B cells and natural killer cells);

  • the number of T lymphocytes, or total T cells (marked as CD3+ on your lab results);

  • the number of CD4+ cells (marked as CD4+ on your lab results; these are mostly helper T cells, but note that although this count is usually discussed as though it refers only to them, it also includes some other cells [monocytes] that are CD4+ positive);

  • the number of CD8+ cells (marked as CD8+ on your lab results; these are the cytotoxic/suppressor T cells);

  • the ratio between CD4+ and CD8+ cells;

  • the number of B lymphocytes (marked as CD19 or CD20); and

  • the number of natural killer cells (marked as CD16 and CD56 on your lab results).

CD4+ Count

After an era of emphasis on viral load when many people seemed to forget the importance of CD4+ counts, it now appears that this tried-and-true measure is probably the single most important indicator of where you are in the course of HIV disease. The general advice is to check on these cells every three to six months. However, during and after times of stress or illness -- known CD4 destroyers -- or at any time when the viral load seems to be rising significantly, it may be important to check them more often.

The test actually calculates the CD4+ count by multiplying the total number of white blood cells times the percentage of white blood cells that are lymphocytes times the percentage of lymphocytes that are CD4+ cells. The CD8+ count is calculated similarly.

The CD4+ count in healthy, HIV negative people has a wide range -- from 400 to 1,500 CD4+ cells per cubic milliliter of blood in men, and 400 to 1,800 CD4+ cells per cubic milliliter of blood in women. There is considerable individual variance in the average count. The lab that does your blood work has a "normal" range, which means that what is "normal" in one lab may not be "normal" in another. However, in most people, repeated test results below 500 CD4+ cells is considered abnormal and a good healthy score would usually be above that range.

It is important to point out that there is a small percentage of people who normally have lower counts and for whom "healthy normal" might be substantially below these counts. Since CD4+ cells are not normally tested until someone is discovered to be HIV positive, most people have no way of knowing what their average count was prior to being infected and, thus, how much decline there may have been prior to their first CD4+ count.

This may be of comfort for those who know that their time of infection was fairly recent but who already have lower counts than would normally be seen after only a short period of infection. They may be needlessly upset by these initial counts, presuming that they're crashing downhill faster than normal, when really their healthy normal count was just fairly low and they're not really decreasing any more rapidly than is common. It is only with repeated tests over time that real trends in CD4+ cell count status can be identified.

CD4+ Percentage

The normal range for percentages of CD4+ cells is from 32% to 50%. It is important to track the changes in this percentage over time because a change of even 3 percentage points in your CD4+ cell percentage is considered significant. It is possible for your CD4+ cell percentage to drop even though your actual CD4+ cell count stays the same, due to changes in the total lymphocyte count.

Remember: the absolute CD4+ count is derived from multiplying the CD4+ percentage by the total number of lymphocytes. Thus, if the total lymphocyte number goes up and the CD4+ percentage goes down, the calculated CD4+ absolute count might stay the same. It is thought that percentages under 20% mean that you may be at risk for Pneumocystis carinii pneumonia (PCP), and below 15% that you are probably at risk of other opportunistic infections.

The CD4+ percentage does not vary as much as the CD4+ count does. When used in combination with the CD4+ count, the CD4+ percentage can give you a good idea of how well your immune system is fighting HIV and may better reflect your immune status when your absolute numbers fluctuate, as they tend to do.

CD8+ Count

In HIV positive people, the CD8+ count rises as these cells attempt to bring HIV infection under control. Researchers believe that the CD8+ cells are producing important protective antiviral factors. The normal range for CD8+ cells is between 375 and 1,100 cells. Some have theorized that, in general, CD8+ counts above 500-600 are a good sign, whereas counts below this range are not, and that a rapidly declining CD8+ count is an early warning that the body's control of HIV is lessening. However, note that CD8+ cell counts usually decline a bit after people start taking potent anti-HIV therapy. This is because the amount of HIV in the blood decreases. Because less HIV is being produced, the immune system reduces the number of CD8+ cells. In addition, it is important to note that one CD8+ cell is not the same as another. There are certain classes of CD8+ cells (in particular, CD38 positive cells) that have been seen to relate to disease progression. Especially in later disease stages, it appears that some of the increases in CD8+ cells that occur may consist, at least in part, of such cells. Thus, although, in general, an increase in CD8+ cells might be seen as a good, protective thing, there are no absolutes on this.

Interpreting Immune Cell Changes

Regardless of the initial count, it is very important to monitor any changes over time. Without treatment, the overall level of CD4+ cells declines in HIV positive people by an average of around 50 to 100 CD4+ cells each year. The lower the CD4+ count, the more damage HIV has done to your immune system. Generally speaking:

  • In HIV positive people not taking treatment, a CD4+ count of about 500 cells suggests mild damage to the immune system.

  • A count between 350 and 500 CD4+ cells suggest moderate damage.

  • The onset of infections or other symptoms related to immune dysfunction usually occurs when the CD4+ cell count drops below 400.

  • Most, but not all, opportunistic infections and conditions occur when the count goes below 200, or the CD4+ percentage falls below 20%. At this point, it is clear that the immune response is seriously compromised.

  • The most common opportunistic infection that occurs in people with CD4+ counts between 100 and 200 is Pneumocystis carinii pneumonia (PCP).

  • Many of the other serious infections, including Mycobacterium avium complex (MAC), cytomegalovirus (CMV) and cryptosporidiosis (crypto), most commonly occur in those with CD4+ counts under 50.

Any substantial decline in CD4+ absolute count or percentage (in the neighborhood of 50 to 100 cells or more, or 3 or more percentage points) that is confirmed by follow-up testing is worrisome, and particularly so if the decline has occurred in a relatively short period of time. A drop that pushes you down to the point where you become vulnerable to infections (for example, dropping from 240 CD4+ cells to 150) would also be cause for more concern than losing the same number of cells when your counts are still relatively high (for example, dropping from 640 to 550 CD4+ cells). That person with 550 CD4+ cells still has relatively good immune function, good protection from opportunistic illnesses, and time to continue watching for trends that may indicate whether or not treatment is looking like a good idea. But the person who has dropped to 150 CD4+ cells is already vulnerable to opportunistic illness and in more pressing need of considering good treatment options, including not only HAART but also prophylaxis (preventive medicine) against the opportunistic infection most likely at this stage -- PCP.

Because many factors -- such as allergies, infections and stress -- can affect immune cell counts on any given day, it is important not to become so CD4+ cell-obsessed that even a minor bouncing around causes undue worry, and to always confirm that a change is "real" with a second test. Again, in the long run, it is the trend of the count over time that is most important. It would never be wise to make decisions about treatment on the basis of a single test. And when any count seems to be out of line with previous tests, consider all the possible factors that might have affected it.

Factors That Affect Immune Cell Counts and Ways to Reduce Variation

First, both CD4+ and CD8+ counts naturally bounce around quite a bit over the course of a day. Usually, the number of CD4+ cells is lowest early in the morning and rises during the day to a high in the evening for people with normal sleep patterns. In people who work night shifts, this pattern reverses. The daily variation is less in HIV positive people than in those who are HIV negative. One study found that between 8 a.m. and 10 p.m., CD4+ counts varied by an average of 506 cells in HIV negative people, but by only 59 cells in HIV positive people. However, even that number of cells could help explain a sudden decrease if you normally have your blood drawn in the late afternoon, and this time you did it first thing in the morning.

Many other factors can affect the CD4+ count:

  • illnesses -- even the common cold -- can worsen the count, but it is usually a temporary decrease (vaccines can have a similar effect):

  • women's CD4+ counts rise and fall at different times during their menstrual cycles;

  • oral contraceptives (birth control pills) may lower CD4+ counts slightly;

  • lack of sleep has been known to temporarily decrease counts;

  • acute stress and periods of depression can also lower CD4+ cell counts;

  • recreational drug use often results in decreased counts, especially for the next few hours, so indulging in a street drug or alcohol might cause a significant decrease;

  • corticosteroid drugs, such as prednisone, can lower counts for many weeks;

  • counts can be temporarily increased after eating or exercise or any time blood pressure is elevated;

  • smokers often have higher counts than non-smokers; and

  • different labs can get different results when they test the same sample of blood.

To help eliminate as many of these test-changing factors as possible, it is best to always try to have your tests done at the same time of day, by the same lab, and, for women, at the same time during the menstrual cycle. The easiest way to avoid some of the likely count variation is to always be tested first thing in the morning, before eating or exercising.

In addition, ask your doctor about rescheduling your blood test, preferably waiting a couple of weeks, if:

  • you have an active infection like a cold or the flu or an outbreak of herpes

  • you've recently stopped or started smoking

  • you've been having trouble sleeping for more than a few days.

If the test can't be rescheduled, make a note of any of these problems. If your test results are unusual, your note may be able to explain them.

Viral Load

Viral load is the amount of HIV in your blood. Viral load tests measure the amount of HIV in a sample of blood. The results are reported as the number of copies of HIV RNA in a millilitre of blood (copies/ml). Viral load tests can measure as few as 20 or more than 1 million copies in the blood sample. The standard test in most common use in Canada measures down to 50 copies, below which your virus is considered undetectable. The so-called ultrasensitive tests can measure down to as few as 20 copies.

It is important to note that although viral load may be "undetectable" this does not mean that HIV has been wiped out. Rather, it means that the amount of HIV being produced in your body is very low -- so low that it can't accurately be counted. If you stop taking your treatment or if HIV develops resistance to your antiretroviral drugs, your viral load will once again become detectable.

In general, a high viral load is a warning signal that CD4+ cells may be heading for a decline and that the risk of disease progression is elevated. For people using antiretroviral treatment, a change in viral load test results is generally considered to be an important measure of the effectiveness of a drug cocktail. The initial goal of treatment is to reach an undetectable viral load within four to 12 weeks of beginning a HAART regimen -- and to keep the reading there long-term. And, on the other end of the treatment spectrum, in someone who has previously been undetectable, an increase in viral load is an indication that the drug combination is no longer working to fully suppress the virus. If several tests confirm that your viral load is staying above detectability, and especially if it has returned to your baseline level (the viral load you had before starting treatment) or is staying above a significant threshold (20,000 to 50,000, more or less), then it may be time to discuss with your doctor why this might be happening. Factors which could cause this problem include:

  • lack of adherence to your drug regimen

  • malabsorption of drugs

  • the inability of today's drugs to fully and permanently suppress the virus in a way that prevents resistance over the long haul

After talking to your doctor, depending on what you both think may be affecting your viral load, it may be time to consider a treatment change.

However, things are never as easy as we'd like them to be, and these generalities have many exceptions. Without any treatment at all, some people with HIV manage to coexist with a viral load of 100,000 or more for years with no apparent immune decline, as evidenced by their stable CD4+ cells. And on the other side are the less lucky in whom a viral load of a mere 10,000 to 20,000 may be enough to cause a downhill slide in immune function, with CD4+ cells that drop and drop. Watching the pattern of CD4+ cells over time and comparing it to viral load results is the only way to identify such people.

For those taking treatment, it is equally important to look at individual variables rather than just using some generic rule. For example, consider that 1-3 month time frame after starting HAART or changing treatment for reaching an undetectable reading. If your viral load was really high to begin with (say half a million or higher), it might take six months to reach the magical undetectable mark. For those who have been undetectable but suddenly start to see virus, especially if it's only a very low level, it is important to know that it may be just a viral "blip," a temporary increase that seems to occur in some people, after which the virus may again disappear with no treatment change. Only repeated tests can distinguish whether the virus is really making a comeback or just briefly poking its head aboveground.

Viral load test results can vary because of changes in your body or in the test procedure. Your viral load can be affected by vaccinations (like a flu shot) or by illnesses because both of these call upon the immune system to respond, and that response activates HIV. As a result, even a cold or sinus infection could cause the viral load to temporarily increase.

As with the CD4+ count, you can reduce some of the variation in your test results by always having your viral load test done at the same lab and at the same time of day. And, again, ask your doctor about rescheduling the test for a couple of weeks if you have any active infection or have recently been vaccinated.

Drug Resistance

One of the characteristics of retroviruses like HIV is that they often make mistakes as they make copies of themselves. These mistakes -- called mutations -- are small, subtle changes in the genetic structure of the virus. Sometimes, these mutations are harmful to the virus and make the virus unable to replicate (make new copies of itself). However, other mutations can allow the virus to replicate even when anti-HIV drugs are being used. Virus that is able to multiply when someone is taking HAART is said to be drug resistant. In contrast, virus that is stopped by antiretroviral drugs is said to be sensitive to those drugs.

The highest likelihood of the development of drug resistance occurs when -- due to skipping doses or taking them irregularly -- you end up with a small amount of drug in the body but not enough to fully suppress the virus. This lets the virus reproduce in the presence of that small amount of drug. And that's when the virus may accidentally mutate into a form that is resistant to the drug(s) you're taking. Then, even when you take the drugs as scheduled, that resistant virus will not be suppressed and, furthermore, it will have an advantage in reproducing itself.

The result is that the viruses that the drugs worked on will be replaced by the resistant ones. The end result is treatment failure -- the drugs will no longer work for you. Because there are a limited number of drugs available, this will limit your future treatment options. This is particularly problematic with drugs that are cross-resistant -- meaning that the development of resistance to one drug in a particular class results in resistance to the others in that class, too. For example, HIV that is resistant to one non-nuke, such as nevirapine, will probably be resistant to the other two non-nukes (delavirdine and efavirenz). With protease inhibitors, if there is high-level resistance to one protease inhibitor, there likely may be cross-resistance to the others.

It is very important to have a discussion with your doctor about the "all or nothing" approach in the following cases -- such as when you have the flu or gastroenteritis or when you are admitted to a hospital. These situations can affect your ability to take your medications (meds) on time as noted below:

  • Infections can cause you to vomit your meals, fluids or meds, and have diarrhea.

  • When you are admitted to a hospital because certain tests need to be performed, you may have to fast or not eat food for prolonged periods. This can cause you to miss doses of your medications.

  • You are in the middle of a difficult or very stressful period of your life.

If you just can't eat or function properly, it may be better to temporarily completely stop taking all your drugs, in the way directed by your doctor, rather than to miss several doses here and there.

The obvious sign that drug resistance may have developed is an increase in viral load. But in order to specifically check whether resistance is present and, if so, to which of the drugs being taken, there are two types of resistance tests that can be used:

  • Genotypic tests identify specific mutations in the virus that can lead to resistance to a particular drug.

  • Phenotypic tests measure the amount of drug it takes to inactivate a sample of virus: the more drug needed, the more resistant the virus is.

Drug resistance tests may be used with people who recently have been infected with HIV (in order to determine if they have been infected with drug-resistant virus) and, more often, for people whose drug cocktail is no longer working (to try to determine which of the drugs is failing). In both cases, the goal is to determine which drugs are most likely to be effective in fully suppressing the virus.

However, it is important to know that the usefulness of these tests is limited. The blood sample that is taken is likely to contain mostly the virus that is currently the dominant population in the body. So, you might receive test results that don't show resistance to X, Y or Z drug, but that is just because the viruses resistant to those drugs didn't end up in the sample. If you then started to take those drugs (X, Y or Z), eventually HIV would develop resistance to them. At some point in the future, your test may then detect some level of resistance to those drugs. In general, a resistance test should be able to rule drugs out, not in. So, you can use it to help find out what drugs are not likely to be working very well, but not to say with certainty which drugs will work.

The risk of developing drug resistance can be reduced by taking all your drugs exactly as they are prescribed. Resistance can only develop when HIV can replicate. The more the virus replicates, the more it can mutate -- and the greater the chances of drug resistance developing. On the other hand, if HAART can shut down HIV replication as much as possible, it will be much less likely for mutations to occur, and drug resistance may be prevented.

Taking drugs precisely as directed is crucial for avoiding drug resistance but can be very difficult over the long haul. Even so ...

  • Always try to follow the instructions you were given for taking your medications (with or without food, with large amounts of liquid, a certain amount of time before or after a meal, etc.).

  • Never, ever skip a dose. Don't say to yourself, "Gee, it's Saturday night and I have a date and I don't want to have gas, so I'll just skip that dose." Or "Gosh, I deserve a vacation from all this. I'll just skip taking the meds this weekend and start over on Monday." That kind of thinking will help give the virus a leg up toward replicating and mutating. The end result for you could be drugs that no longer work and, eventually, no remaining treatment possibilities.

The far better answer is to choose from among your available combinations (based on your treatment history and, if available, resistance testing results) the one that causes you the least problems. And then consider all the strategies discussed in CATIE's Practical Guide to HIV Drug Side Effects to manage any remaining side effects.

In Canada, drug resistance tests are not widely available yet. They are freely available through some specialist HIV clinics in the larger cities. Some provincial public health labs are checking the tests to find out which ones give the most accurate and reliable results. Both types of tests are expensive.