Lab Tests and Why They Are Important
As part of your HIV care, your provider will order several laboratory tests. The results of these lab tests, along with your physical exam and other information you provide, will help you and your provider work together to develop the best plan to manage your HIV care so that you can get the virus under control, protect your health, and reduce the chance that you will pass the virus to others.
Your healthcare provider will repeat some of these tests as part of your ongoing HIV care to continue to assess your health and how well your HIV treatment is working.
The lab tests may include:
- CD4 count: CD4 cells are a type of white blood cell. They are specialized cells of the immune system that are destroyed by HIV. A CD4 count measures how many CD4 cells are in your blood. The higher your CD4 cell count, the healthier your immune system. The CD4 count of an uninfected adult/adolescent who is generally in good health ranges from 500 cells/mm3 to 1,600 cells/mm3. In contrast, if HIV has destroyed so many CD4 cells that you have a CD4 count of fewer than 200/mm3, you are considered to have progressed to stage 3 (AIDS), the most advanced stage of HIV infection.
Why it’s important: A CD4 count is a good measure of your risk of opportunistic infections and an indicator of how well your immune system is working. Treatment with antiretroviral therapy (ART), medications that control the HIV, is recommended for everyone with HIV, no matter how high or low their CD4 count is. However, a low CD4 count (below 200/mm3) increases the urgency to start ART.
- CD4 Percentage: This measures how many of your white blood cells are actually CD4 cells. This measurement is more stable than CD4 counts over a long period of time, but, for most people, the CD4 count remains a more reliable measure of how well your immune system is working than the CD4 percentage.
Why it’s important: This measurement is less likely to vary in between blood tests than CD4 counts (which can vary from month to month or day to day).
- Viral Load (VL): An HIV viral load test, also called an HIV RNA test, tracks how many HIV particles are in a sample of your blood. This is called your viral load.
Why it’s important: A goal of HIV treatment is to keep your viral load so low that the virus can’t be detected by a viral load test. It’s important to get a viral load test to see the level of HIV in your blood before starting treatment and help guide the choice of HIV medications and then to get repeat tests to track your response to HIV treatment.
- Complete Blood Count (CBC): This is a measure of the concentration of red blood cells, white blood cells, and platelets in a sample of your blood.
Why it’s important: A CBC is one of the most commonly ordered blood tests. It can reveal infections, anemia (abnormality in your red blood cells), and other medical issues.
- Drug Resistance Tests: HIV can change form, making it resistant to some HIV medicines. A drug resistance test helps your provider identify which, if any, HIV medicines will not be effective against the strain of HIV you have.
Why it’s important: Drug resistance test results help your provider determine which HIV medicines are most likely to work for you.
- Serum Chemistry Panel: This panel is comprised of a series of several blood tests and helps provide information about your body's metabolism. It gives your provider information about how your kidneys and liver are working, and can be used to evaluate your blood sugar levels, calcium levels, and phosphorous levels.
Why it’s important: Some HIV medications can have serious side effects, and this test helps your provider monitor the impact of your medications on your body’s ability to function normally.
- Sexually Transmitted Disease (STD) Screening: These screening tests check for syphilis, gonorrhea and chlamydia.
Why it’s important: STDs can also cause serious health problems if not treated Having an STD also can increase your risk of transmitting HIV to others.
- PAP Test (Cervical and Anal): A cervical Pap test (or Pap smear) looks for cancers and precancers in a woman’s cervix. The cervix is 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.
Why it’s important: For women living with HIV, abnormal cell growth in the cervix is common, and abnormal anal cells are common for both men and women living with HIV. These abnormal cells may become cancerous if they aren’t treated.
- Hepatitis A, B, and C Tests: These blood tests check for current or past infection with Hepatitis A, B, or C.
Why it’s important: Some people who are living with HIV are also coinfected with hepatitis. 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.)
- Tuberculosis Test: This blood test checks for TB infection. If the TB blood test is not available, a TB skin test should be performed.
Why it’s important: Untreated TB can be a deadly disease for people living 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.
Why it’s important: Toxoplasmosis can be a deadly opportunistic infection for people living with HIV. Your clinician needs to know if you have been exposed to the parasite that causes toxoplasmosis or are at risk for exposure. This will help your healthcare 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.
- 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. You should not to eat for several hours before these blood tests.
Why it’s important: 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 before starting treatment to help guide the choice of medications and to treat high lipids to avoid other serious health problems.
- Fasting Glucose (blood sugar) Test: This test measures your blood sugar levels to check for signs of diabetes. You should not to eat for several hours before this blood test.
Why it’s important: Some HIV medications can affect blood sugar levels, potentially leading to complications like diabetes. It’s important to get a glucose test to know what your blood sugar is before starting 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.)
- Pregnancy Test: This test shows whether a woman is pregnant or not.
Why it’s important: If 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. You and your health care provider can discuss steps you can take prevent transmitting HIV to your baby.