Lab Tests and Why They Are Important
Before you start treatment with HIV medicine (called antiretroviral therapy or ART), your health care provider will order several baseline lab tests. You may start treatment or be referred for treatment before the test results are in.
Your lab test results, along with your physical exam and other information you provide, will help you and your provider work together to manage your HIV care.
Your health care provider will repeat some of these lab tests as part of your ongoing HIV care to see how well your HIV medicine is working so that you can get the virus under control, protect your health, and prevent transmitting the virus to others.
Viral Load Test
One important test is your HIV viral load test. It’s a lab test that measures how many HIV particles are in a sample of your blood. This is called your viral load. You want your viral load to be low. The higher your viral load, the greater your risk of becoming ill because of HIV and the more likely you are to transmit HIV. The viral load is highest during the acute (early) phase of HIV, and when a person is without treatment.
Why it’s important: Taking HIV medicine can make your viral load very low--so low that the virus can’t be detected by a viral load test. This is known as having an undetectable viral load. People with HIV who take HIV medicine as prescribed and get and keep an undetectable viral load can live long, healthy lives and have effectively no risk of sexually transmitting HIV to their HIV-negative partners. An undetectable viral load does not mean there is no HIV in your body. It means that the amount of HIV in your blood is too low to be measured in a standard viral load test. HIV is still in your body and will rebound to detectable if you stop taking HIV medicine.
CD4 Cell Count
A CD4 cell count measures how many CD4 cells are in your blood. CD4 cells are infection-fighting cells of the immune system. As HIV disease advances, your CD4 count drops. The higher your CD4 cell count, the healthier your immune system. The CD4 count of an adult/adolescent who is generally in good health ranges from 500 to 1,200 cells/mm3. In contrast, if a person has a CD4 count of fewer than 200/mm3, they are considered to have progressed to stage 3 (AIDS), the most advanced stage of HIV.
Why it’s important: A CD4 cell count is a good measure of how well your immune system is working and your risk of opportunistic infections. Treatment with ART is recommended for everyone with HIV, no matter how high or low their CD4 count is.
Once you’ve started HIV treatment, CD4 cell count and viral load tests are used to monitor whether your HIV medicines are working effectively to control your HIV. If the test indicates your medicines aren’t working, your doctor can prescribe different ones that may work better.
Other Important Lab Tests
There are other lab tests that will help your health care provider get important information about your health and work with you to choose the right HIV medications for you.
Blood Chemistry Tests: This group of tests measures several different chemicals in your blood to help monitor the health of your organs, especially your heart, liver, and kidneys. Health care providers use these tests to look for side effects caused by HIV medicines.
CD4 Percentage: This is a measurement of how many of your white blood cells are actually CD4 cells. CD4 cell counts are typically used to assess a person’s immune function, but a CD4 percentage can also be used. A CD4 percentage is less likely to vary in between blood tests than CD4 counts, which can vary from month to month or day to day.
Complete Blood Count (CBC): This test measures the concentration of red blood cells, white blood cells, and platelets in a sample of your blood. A CBC is one of the most commonly ordered blood tests. It helps your health care provider keep track of your overall health and spot infections or other potential medical problems.
Drug Resistance Tests: HIV can change form, making it resistant to some HIV medicines. A drug resistance test helps your health care provider identify which, if any, HIV medicines will not be effective against the strain of HIV you have and choose which HIV medicines are most likely to work for you.
Fasting Glucose (Blood Sugar) Test: This test measures your blood sugar levels. Some HIV medications can affect blood sugar levels, potentially leading to complications like diabetes. It’s important to get a glucose test when you start HIV treatment to help guide the choice of HIV medications and then to get repeat tests to monitor possible increases in your blood glucose. (Read more about diabetes and people living with HIV.)
Fasting Lipid Panel (Cholesterol and Triglycerides): Lipids are fat or fat-like substances found in the blood and body tissues. These tests measure your lipid levels, including cholesterol and triglycerides. That’s important because some HIV medications can affect your cholesterol levels and the way your body processes and stores fat. High lipids can make you prone to other medical problems, including heart problems. It’s important to know what your lipids are when you start treatment to help guide the choice of medications and to treat high lipids to avoid other serious health problems.
Hepatitis A, B, and C Tests: Some people with HIV also have viral hepatitis. These blood tests check for current or past infection with Hepatitis A, B, or C. Checking you for hepatitis A, B, and C infection can help your provider to determine if you need to be treated, or if you are a candidate for one of the existing hepatitis A or B vaccines. (Read more about how hepatitis affects people living with HIV.)
PAP Test (Cervical and Anal): A cervical Pap test (or Pap smear) looks for cancers and precancers in a woman’s cervix—the lower part of a woman’s uterus (womb), which opens into the vagina. The test involves using a swab to take cell samples directly from the cervix. An anal Pap test can be done on a male or female; it involves a swab to take a cell sample from the anal canal. For women living with HIV, abnormal cell growth in the cervix is common, and abnormal anal cells are common for both men and women with HIV. These abnormal cells may become cancerous if they aren’t treated.
Pregnancy Test: This test shows whether a woman is pregnant or not. If you have HIV and you are pregnant, you can greatly lower your risk of passing HIV to your baby and protect your own health by taking ART during pregnancy, labor, and delivery.
Sexually Transmitted Disease (STD) Screening: These screening tests check for syphilis, gonorrhea and chlamydia. STDs can cause serious health problems if not treated. Having an STD also can increase your risk of transmitting HIV to others.
Tuberculosis (TB) Test: This blood test checks for TB infection, an infection usually spread by breathing in air that has been contaminated by someone with TB of the lungs. If a TB blood test is not available, a TB skin test is typically performed. This test is important because untreated TB can be a deadly disease for people with HIV. Early screening and treatment will help limit your risk of severe illness, as well as lower your chances of transmitting TB to others if you do have it.
Toxoplasmosis Screening: This test checks for past exposure to a parasite that can cause severe damage to the brain, eyes, and other organs in people with weakened immune systems. Toxoplasmosis can be a deadly opportunistic infection for people with HIV. Your health care provider needs to know if you have been exposed to the parasite that causes toxoplasmosis or are at risk for exposure. This will help your provider to decide if you need preventive treatment. If your CD4 count falls below 100/mm3, you will probably need to do another screening, even if your earlier screens were negative.
Frequency and Timing of Testing
After you start HIV treatment, not all lab tests will be conducted at every medical visit. Some will occur every few months. Others will depend on whether you are stable on HIV treatment and doing well. View this chart about the timing of various tests and talk to your provider about what is recommended for you.