Keeping Track of HIV Infection
All people with HIV infection should have regular medical care. Options for medical care will depend to some extent on the resources available (see chapter 7; options for financing this care are discussed in chapter 9).
Regular medical care usually includes medical evaluations every three to four months. During the visits, your previous medical problems should be reviewed, and any symptoms or conditions that may or may not be related to HIV infection should be discussed. During the visits, you should also have a physical examination and any necessary laboratory tests. Your physician should then candidly discuss your health status with you and should recommend subsequent medical care.The principal laboratory tests are the CD4 cell count and the HIV viral load test. These tests are usually given to all people with HIV infection every three to four months. The purpose of the CD4 count is to evaluate the state of the immune system. The purpose of the viral load test is to evaluate the prognosis based on the rate of viral reproduction. The two tests are complementary. A low CD4 count means vulnerability to complications regardless of the viral load. And the viral load gives the speed of progression regardless of the CD4 count. These tests are critical to making good decisions for treatment: the CD4 count shows how vulnerable the person might be to the complications of HIV, and the viral load shows how well treatment is working.
Viral Load Test
The viral load test, introduced in 1996, measures the number of HIV in a given amount of blood. The terms viral load and viral burden are used synonymously; the proper scientific term is quantitative plasma HIV RNA. The results are reported as “copies per milliliter,” meaning the number of viruses per milliliter of blood. Although this test measures the amount of HIV in the blood, over 95 percent of the HIV is in the lymph system.
But the total amount of HIV in the body is accurately represented by the amount of HIV in the blood.The viral load indicates prognosis. The average viral load of someone who has had no treatment is 30,000 to 50,000 copies per milliliter. People who have high amounts of virus, like 100,000 or 1,000,000, and who aren’t taking treatment will have a disease that tends to progress rapidly and CD4 cells that decline quickly. They will develop AIDS sooner and live for a shorter time. People who have a low viral load, like 1,000 or 10,000, and who aren’t taking treatment will have a disease that progresses relatively slowly and CD4 cell counts that decrease relatively slowly. They will live relatively longer. Therefore, both the CD4 count and the viral load predict the course of the disease. If the CD4 count is low and the viral load is high, the prognosis (without treatment) is poor. If the CD4 count is high and the viral load is low, the prognosis is good.
The viral load is most useful for monitoring people’s responses to treatment. When people take antiretroviral treatment, the viral load decreases rapidly and dramatically, at least ten-fold or a hundred-fold and within two to four weeks. For example, a person with a viral load of 100,000 who receives antiretroviral treatment on January 1 will, on February 1, often have a viral load of 10,000 (a ten-fold or one log decrease) or 1,000 (a hundred-fold or two log decrease). The viral load varies, depending on how the test is done. This variation is about three-fold; that is, a result showing 10,000 copies of HIV might really be 3,000 or 30,000 copies. The viral load also varies with different methods of doing the test; so the same laboratory and the same methods should be used for repeated tests over time.
One goal of therapy is to get the viral load down to where it is undetectable, meaning that it’s less than the arbitrary threshold of the test, usually less than 50 copies per milliliter. The second goal of therapy is to keep the viral load down as long as possible.
When the amount of virus is this low, the virus is reproducing only minimally and the disease does not progress. Fewer viruses also mean fewer mutations—that is, fewer new genes that make the virus resistant to drugs—so the benefit of knocking back the virus is likely to last.CD4 Cell Count
The CD4 cell count is an indicator of the status of the immune system. The CD4 cell count measures the concentration of CD4 cells in a given amount of blood; for example, a CD4 count of 1,000 means 1,000 CD4 cells per milliliter of blood. The CD4 count for a healthy person is 500 to 1,450; 95 percent of people without HIV infection have counts in this range. Counts above 500 are usually considered normal. Counts of less than 500 mean the immune system has been damaged; counts of less than 350 mean the damage is moderate; counts of less than 200 mean the damage is severe; and counts of less than 50 mean the disease is advanced but not irreparable. Most people do not get the complications of HIV infection until their CD4 counts are less than 200, which is the threshold used to define AIDS. These complications aren’t actually common until the CD4 counts are less than 50.
When the new drugs control HIV, people’s CD4 counts increase in both number and quality. That is, the CD4 count goes up and the new CD4 cells work like they’re supposed to. The average increase, if viral load is low, is about 50 to 100 or 150 the first year, and then about 100 per year thereafter. This means that if a person with a CD4 cell count of 50 started treatment, and the treatment brought the viral load down to undetectable, the CD4 count would increase to 100 to 200 in one year. Many people, even if their counts were well below 50 to start with, have counts that go up in several years to 500 or more.
The relation between viral load and CD4 count, however, is not invariable and differs in different people. Many people whose treatment is not completely controlling the virus still have CD4 counts that go up; the counts, however, don’t usually go up as fast or as high as when the virus is completely suppressed.
Sometimes physicians call an increasing CD4 count despite persistent high levels of virus the “viral load-CD4 disconnect” or “discordant.” We don’t know why people with the same degree of viral suppression can have differing responses in their CD4 counts. When the virus is suppressed and the CD4 count doesn’t respond, we consider changing regimens. In most cases, however, people continue on the regimen that suppressed the virus. We do know that these people seem relatively well protected from HIV complications.You need to be cautious in interpreting the CD4 cell count. As with the viral load test, the count can vary with the laboratory technician and the method used to do the test: the same laboratory technician doing the same test twice on the same blood sample can show counts that differ by 30 percent, so that a count of 500, if repeated, might be 350 or 650. Two laboratories working on the same specimen might show results of 70 and 130, or 140 and 260, or 210 and 390, or 280 and 520, and so on.
Other factors alter CD4 counts. The CD4 count is highest in the evening and lowest at noon. It is also lower after heavy exercise or when you have an infectious disease like influenza. We emphasize this because many people have unrealistic expectations of the test and become alarmed when the count decreases slightly. But the CD4 cell count is not particularly fine-tuned, and modest decreases from one test to the next— for example, from 500 to 400—are considered to be “within the error of the test.” Repeated tests showing trends over long periods are far more reliable than any isolated sampling. When major decisions about treatment depend on the CD4 count, or when a value for the count doesn’t make sense, the usual recommendation is to repeat the count. Almost everyone with HIV infection knows his or her CD4 counts and has them measured at periodic intervals, usually every three to six months.
The cost of the test is usually $40 to $100, and no one seems to know why the charge varies so enormously.