Together with regular medical care, good adherence, and a healthy lifestyle, the following blood tests can be very important in the management of HIV. Speak to your doctor about how you can use these tests to help make treatment decisions.

Viral load is the amount of HIV in your bloodstream. It is measured by a polymerase chain reaction or PCR test (also called a viral load test). Viral load tests are an important tool to:

• Monitor HIV progression:
  While CD4 cell counts are your best measurement of how healthy your immune system is today, viral load tests can help you figure out whether you’re at risk for more immune damage in the near future. When compared over time, results tell you whether HIV is reproducing at a steady, fast, or slow rate. The higher your viral load, the more likely you are to lose CD4 cells
• Figure out when it’s time to start treatment:
  People with higher viral loads seem to be at greater risk for HIV-related complications, including death. U.S. Treatment Guidelines suggest that anyone with a viral load above 55,000 consider treatment. (Some doctors prefer to use CD4 counts to guide decisions about when to start treatment in HIV+ women.)
• Measure how well HIV drugs are working:
  HIV drugs work by preventing the virus from reproducing. If the drugs are working, your viral load should go down. If there is a problem, your viral load may go up.

The goal of HIV treatment is to keep viral load as low as possible for as long as possible. With effective HIV treatment regimens, viral load can be reduced to levels that cannot be detected by lab tests. With most viral load tests this is below 50 copies.

Have a viral load test when you are first diagnosed and every three to four months when you are not on HIV therapy.

Have a viral load test before starting treatment and another one two to eight weeks later. If the regimen is working, your viral load should drop by 90% within two months and be undetectable (less than 50 copies) within six months of starting treatment. If these levels are achieved, viral load is usually measured every three to six months.

If these levels are not achieved after starting treatment, or if your viral load has recently become detectable on stable therapy and keeps increasing, it can signal that your regimen isn’t controlling HIV as well as it should. You and your doctor should consider all possible reasons (problems with absorption, adherence, or drug resistance) and take steps to correct the problem, including considering changing drug treatments.

Resistance tests are used to determine which drugs will work best against your virus. There are several types of resistance tests available.

Genotype tests analyze the genetic makeup of your virus. They look for changes (mutations) in HIV’s enzymes that can make it harder for drugs to work effectively. Your test result will list any mutations found.

Each drug is associated with a mutation or mutations that can make that drug less effective. Some HIV drugs don’t stop working unless multiple mutations are present.

We still don’t know everything about these mutations, or which combinations of them are most problematic. Because of this, it can sometimes be difficult to figure out how to make treatment decisions based on genotype results.

The phenotype test cultures (grows) your virus in a laboratory. It is then placed in test tubes containing samples of the various HIV drugs. If a certain drug is not able to control the virus, more of that drug is added to the test tube. Depending on how much drug is needed, the lab can determine how resistant the virus is to the drug.

Phenotypic resistance results are reported as susceptible, sensitive, or less susceptible. Susceptible means that the drug will probably work well. Sensitive means that the drug will work as expected in the average person and less susceptible means the drug will probably not work very well for you.

Phenotype test results are easier to interpret than genotype.

This is a genotype test that goes one step further – it uses phenotype data from many patients to predict whether your virus will be sensitive or resistant to each of the HIV drugs.

None of the resistance tests are perfect. They cannot detect every mutation in your HIV or be used to predict exactly which drugs will work for you. However, they are quickly becoming another tool to determine treatment options in certain situations such as:

• Someone who was just infected with HIV, also called acute infection (testing is used to see if the person was infected with a drug-resistant strain)
• Someone who is failing his or her current regimen (testing is used to guide the choice of a new regimen)
• A pregnant woman (testing is used to determine the best regimen to prevent mother-to-child HIV transmission)

All resistance tests should be taken while you are still on HIV drugs to get the best results.

When any drug is approved, a standard dose is determined. This dose may be safe and effective for most people, but for some people, it may be more or less than needed. If people get too little of an HIV drug, it may be less effective and lead to the development of resistance. If they get too much, they may have problems with side effects.

Therapeutic drug monitoring (TDM) measures levels of drugs in the bloodstream. Based on the results, doctors may be able to adjust doses as necessary in different individuals. Ideally, this should reduce side effects from too much drug in the blood stream and minimize the potential for drug resistance from too little.

Drug level testing may be particularly helpful for HIV+ women. Some women have higher levels of certain drugs in their bloodstreams and experience more side effects than men.

These sex (male vs female) differences may be related to hormone changes that occur when women get their periods. Drug level differences also may be linked to basic biology and physiology of cells (there are differences in the cells of men and women). They may also be linked to weight differences.

TDM is not approved for use with HIV drugs yet and there are still unresolved issues regarding the practical application of results. But the hope remains that TDM can lead to better-tolerated regimens and more knowledge about HIV drugs in women.

1		Anastos, K. et. al. (2002). The women’s interagency HIV study collaborative study group. Archives of Internal Medicine, 162. 1973-1980.
2		Kashuba, A. (2002). Overview of sex differences in pharmacology. Presentation for AACTG Pharmacology Committee.
3		NATAP. (2003). Knowledge of genotypic resistance mutations among providers of care to patients with Human Immunodeficiency Virus. Retrieved October 2004 from http://www.natap.org/2003/Jan/012403_3.htm.
4		United States Department of Health and Human Services. (2004). Guidelines for the use of antiretroviral agents in HIV-infected adults and adolescents. Retrieved October 2004 from http://aidsinfo.nih.gov/guidelines/default_db2.asp?id=50.