Having regular lab tests is a necessary part of good health care. Lab tests are important tools that help you and your health care provider keep track of how you are doing in the following areas:

Immune system status

• How HIV is affecting your immune system
• If you need to start or switch HIV drugs
• Example of lab test: CD4 cell test (see sheet called Understanding CD4 Cells and CD4 Cell Tests)

Overall health

• How your body systems are functioning
• If you have side effects from the drugs
• If you are having problems that are not related to HIV
• Examples of lab tests: complete blood count, blood chemistry tests, blood fat and sugar tests (see sheet called Understanding Lab Tests I)

HIV illness

• How HIV is responding to the drugs you are taking
• Which drugs to use
• The specific characteristics of your virus
• Examples of lab tests: viral load test, resistance test, tropism test (explained in this sheet)

Viral load is the amount of HIV in your bloodstream. Viral load can be measured by two different lab tests: polymerase chain reaction (PCR) or branched DNA (bDNA). It is best to stick with the same kind of test and not switch between the two or it will be difficult to compare results over time.

Viral load results are reported as copies of HIV in one milliliter of blood. Numbers can range from about one million copies to as few as 50 copies. If you have less than 50 copies, your health care provider may tell you that your results are “undetectable.”

Being undetectable is the best result because it means your virus is under control. However, undetectable does not mean that you have been cured of HIV; it just means that there is not enough virus for the test to measure (below 50 copies).

Viral load tests are an important tool to:

• Monitor HIV progression
  When compared over time, viral load results show if the amount of HIV in your bloodstream is higher or lower than it was before. The higher your viral load, the greater the chances of your immune system being damaged.
• Measure how well HIV drugs are working:
  HIV drugs work by preventing the virus from making copies of itself (reproducing). If the drugs are working, your viral load should go down. If there is a problem, your viral load may go up.

One goal of HIV treatment is to keep viral load levels as low as possible for as long as possible. This gives you the best chance of staying healthy. With effective HIV treatment regimens, viral load can be reduced to undetectable in many people. This means that your HIV medications are working and you should continue to take them. HIV is still in your body. If you stop taking your HIV drugs, the virus usually starts reproducing and your viral load will go up.

• If you are not on HIV treatment, have a viral load test
  • When you start receiving HIV care
  • Repeat test every three to six months
• When you start treatment, have a viral load test
  • When starting and two to eight weeks after treatment was started
  • Repeat test every one to two months until viral load becomes undetectable
• Once you are on a stable treatment regimen and undetectable, have a viral load test
  • Every three to six months
• When you change treatment, have a viral load test
  • When changing and two to eight weeks after treatment was changed
  • Repeat test every one to two months until viral load becomes undetectable
    

If your HIV drugs are working, your viral load should become undetectable within six months of starting treatment. If this does not happen or if your viral load becomes detectable after being undetectable on a stable treatment regimen and keeps increasing, it can signal that your regimen isn’t controlling HIV as well as it should.

You and your health care provider should consider all possible reasons if your viral load is detectable; this includes problems with absorbing the drug into your body, trouble sticking to the regimen, or development of drug resistance (info on drug resistance in section below). You will then need to take steps to correct the problem, including additional testing and considering changing drug treatments.

Even though HIV drugs are designed to stop the virus from reproducing, sometimes HIV changes in such a way that it is able to overcome the effects of a drug. These changes to HIV are called mutations. Some mutations prevent certain HIV drugs from working. When this happens we say that HIV has developed resistance to that drug.

Resistance decreases the ability of HIV drugs to control your virus and knocks out your treatment options. The best way to prevent resistance is to stick closely (adhere) to your HIV drug regimen. With good adherence, resistance is less likely to develop.

Drug resistance tests are used to determine if your virus has developed resistance to HIV drugs. There are several types of resistance tests available.

• Genotype test
  This test uses HIV from your blood to check for mutations that cause drug resistance
• Phenotype test
  This test challenges your virus with all HIV drugs (in a test tube) to determine which ones are still effective against your HIV
• Virtual phenotype test
  This is a genotype test that goes one step further – it uses phenotype information to predict which drugs will be effective against your virus (and its mutations)
  

In most cases, the genotype is the preferred test. For people who have been on HIV treatment before and may have HIV that is resistant to a number of different drugs, including protease inhibitors, the phenotype test may be done in addition to the genotype.

Resistance testing is recommended for:

• People who have just become infected with HIV, whether or not they are going to take HIV drugs right away
• People who have never taken HIV drugs and are starting to receive medical care, whether or not they are going to take HIV drugs right away
• People who have never been on HIV drugs and are planning to start
• People who are on HIV drugs and see their viral load go up
• People who have recently started HIV drugs and their viral load is not coming down enough
• HIV+ pregnant women

Resistance testing is not usually recommended for:

• People who have stopped HIV drugs for four weeks or more
• People with a viral load below 500 copies

Resistance tests are helpful when choosing a drug regimen. The tests are only a guide, however. Other factors, such as past medications, side effects, and adherence must be taken into account as well.

Tropism has to do with the way HIV infects white blood cells in your body called CD4 cells. In order to enter a CD4 cell, HIV attaches itself to receptors on the outside (surface) of the cell.

Each CD4 cell has a CD4 receptor and two co-receptors called CCR5 and CXCR4 on its surface. To enter the CD4 cell, HIV must attach to the CD4 receptor and either the CCR5 or the CXCR4 co-receptor.

HIV that uses CCR5 to enter the cell is called CCR5 tropic or R5 virus. HIV that uses CXCR4 is called CXCR4 tropic or X4 virus. Virus that uses both co-receptors is called dual or mixed tropic.

Finding out the tropism of HIV is important because there is a class of HIV drugs that work against CCR5 tropic HIV. This class is called CCR5 antagonists or entry inhibitors. CCR5 antagonists work by attaching to the CCR5 co-receptor on the CD4 cell’s surface. This blocks HIV from attaching to the CCR5 co-receptor of that CD4 cell. If HIV cannot attach to the CD4 cell, it cannot enter and infect the cell. CCR5 antagonists work best for people whose HIV is CCR5 tropic.

Tropism testing lets your health care provider know if you have CCR5 tropic virus. You must take this test if you are thinking of taking a CCR5 antagonist. At this point there is only one CCR5 antagonist available called Selzentry (maraviroc), but there are others in development.

Regular lab tests are very important in the management of your health and your HIV. Speak to your health care provider about when you need to take the above tests and how they can be used to help you make treatment decisions.