for Veterans and the Public
Laboratory Tests and HIV: Entire Lesson
Understanding laboratory tests
Laboratory tests can help keep tabs on your health. Some of these tests will be done soon after you learn you are HIV positive. Then depending on your immune status, whether you are on medication or not, and a variety of other factors, your provider will set up a schedule for you.
The lab tests look at:
- how well your immune system is functioning (CD4 count)
- how rapidly HIV is replicating, or multiplying (viral load)
- how well your body is functioning (tests to look at your kidneys, liver, cholesterol, and blood cells)
- whether you have other diseases that are associated with HIV (tests for certain infections)
The first set of lab tests ideally is done shortly after you find out you have HIV, and the results establish a starting point or "baseline." Future tests will let you know how far from this baseline you have moved. This can help you tell how fast or slow the disease is moving and indicate whether treatments are working.
Most labs include a "normal" range (high and low values) when they report test results. The most important results are the ones that fall outside these normal ranges. Test results often go up and down over time so don't worry about small changes. Instead look for overall trends.
What follows are descriptions of the most common tests:
- CD4 count
- HIV viral load
- Resistance test
- HLA B*5701
- Complete blood count
- Blood chemistry tests
- Fasting lipid profile
- Tuberculosis test
- STD screening
- Hepatitis A, B, and C
CD4 count (or T-cell count)
CD4 cells (also known as CD4+ T cells) are white blood cells that fight infection. CD4 cell count is an indicator of immune function in patients living with HIV and one of the key determinants for the need of opportunistic infection (OI) prophylaxis. CD4 cell counts are obtained from bloodwork as part of laboratory monitoring for HIV infection.
CD4+ cell counts are usually measured when you are diagnosed with HIV (at baseline), every 3 to 6 months during first 2 years or until your CD4 count increases above 300 cells/mm3. Otherwise your CD4+ cell count may be measured every 12 months. Most people who are on HIV treatment can expect an average increase of about 50-100 cells/mm3 a year. Patients who initiate therapy with a low CD4 count or at an older age may not have the same increase in their CD4 count despite virologic suppression.
There are multiple factors that affect your CD4 count. Taking your medication is one way to keep your count high but medications or acute infections are among the things that could affect the CD4 count. If you are responding well to your medications, you may need less frequent testing going forward.
HIV viral load (or 'HIV RNA')
HIV viral load tests measure the amount of HIV in the blood. Lower levels are better than higher levels. The main goal of HIV drugs is to reduce the HIV viral load to an "undetectable" level, meaning that the HIV RNA is below the level that the test is able to count.
The lower limit of HIV RNA detection depends on the test used--some go down to 50 copies/ml, while other go as low as 20. High viral loads are linked to faster disease progression. Reducing the viral load to "undetectable" levels slows or stops disease progression and prevents HIV transmission to sex partners. Treatment for HIV suppresses the virus but does not eliminate it. Even if HIV levels are not detectable in the bloodstream, HIV is still in the body and will rebound to detectable if the HIV medicines are stopped.
The lower your viral load, the better.
CD4 counts and HIV viral load tests are usually done when you first see a medical provider and about every 3 months afterwards. Results tell whether the HIV medications are working well; and for people who have chosen to delay taking medicines, they can help you and your provider monitor your health and decide how urgent it is for you to start taking HIV drugs or medicines to prevent infections (more on this in Treatment Decisions).
Resistance test (HIV Genotype)
This test determines whether the particular virus in your body is resistant to HIV medications.
HIV reproduces rapidly and, as the virus makes copies of itself, small changes (or mutations) sometimes result. These changes can lead to different HIV strains, particularly if the person is taking (or has taken) HIV medicines but the HIV virus is not completely controlled or suppressed. If a strain that is resistant to your HIV drugs develops, the virus will be able to grow even though you are on medication. Your viral load will start to rise. The resistant virus soon will become the most common strain in your body. If this occurs, your provider may order a resistance test to check for mutations in the HIV virus.
A person can be infected with a drug resistant strain of HIV if the infection was from an individual with resistant virus. For this reason, an HIV resistance test is recommended for all people as soon as they are diagnosed with HIV.
Therefore, resistance testing is performed upon diagnosis of HIV and if a medication regimen is no longer keeping the viral load suppressed.
Pop question: True or false. Resistance refers to certain strains of the HIV virus that do not respond to HIV drugs.
Pop question: True or false. Resistance refers to certain strains of the HIV virus that do not respond to HIV drugs.
Answer: TRUE. Resistance refers to certain strains of the HIV virus that do not respond to HIV drugs. This happens when the virus undergoes a change that makes the HIV drugs no longer effective.
Complete blood count (CBC)
This test looks at the different cells in your blood, including red blood cells, white blood cells, and platelets.
- Red blood cells carry oxygen to other cells in your body. If the level of your red blood cells is too low, you have anemia. Anemia can cause fatigue. Tests that look at your red blood cells include hemoglobin and hematocrit. Hematocrit refers to the percentage of your blood that consists of red blood cells. A normal hematocrit is about 37-47% in females and 40-54% in males.
- White blood cells come in many types, and all are involved in your immune system's effort to keep you healthy (the CD4 cell is a type of white blood cell). High white blood cell counts may indicate that you are fighting an infection. Low counts may put you at risk of getting an infection.
- Platelets help with clotting, so if your platelets fall too low, your blood may not clot well. You may bleed more than usual, for example, when you brush your teeth or shave your skin. As the platelet count falls, the chance of internal bleeding rises.
These tests are usually done every 3 to 6 months, unless your lab values are fluctuating a lot, or you have symptoms of HIV disease. Then the tests may be done more often.
Blood chemistry tests
Chemistry tests examine the levels of different elements and waste products in the blood and help determine how well different organs are functioning. Usually, the tests are divided into two panels:
- Electrolyte tests (sometimes called "lytes") and kidney function--These tests help measure how well your kidneys are working, and measure the balance of fluids, acids, and sugar in your body. They include tests for sodium, potassium, chloride, blood urea nitrogen (BUN), creatinine, and glucose.
- Liver function tests (LFTs)--These tests measure whether your liver is being damaged. (Things that can damage the liver include viral hepatitis, alcohol, street drugs, and certain medications.) These tests measure alkaline phosphatase, ALT, AST, albumin, and bilirubin.
Blood chemistry tests are usually done every 3 to 6 months. It is important to have these done at baseline and while you are on HIV medications to make sure the medications are safe for your kidneys and liver.
The level of certain fats in the blood can give clues to your risk of heart disease. Cholesterol and triglycerides are important for health, but too much of them in the blood can cause fatty deposits to form in the arteries. This increases the chances of a heart attack. Too much triglyceride can also lead to pancreatitis, a serious inflammation of the pancreas. High cholesterol and high triglycerides can occur in people living with HIV. They can also be a side effect of some of the older HIV medications.
Cholesterol is measured by three different tests:
- Total cholesterol
- HDL (high-density lipoprotein), often referred to as "good" cholesterol because high levels lower your risk of heart disease
- LDL (low-density lipoprotein), often referred to as "bad" cholesterol because high levels raise your risk of heart disease
These tests are usually done at least once a year, and more often if your levels are high or you require medication to control triglyceride and cholesterol levels. Your provider may want the lipid panel to be done while you are fasting, which means nothing to eat or drink (except water) after midnight the night before the test. This gives the most accurate evaluation of the cholesterol and triglycerides in the blood. Be sure to ask your provider if the blood tests are recommended to be done fasting.
TB is short for tuberculosis, an infection usually spread by breathing in air that has been contaminated by someone with TB of the lungs. Most people who are exposed to TB don't get sick from it-the bacteria can live in the body for a long time without causing disease. But some people who carry the bacteria develop tuberculosis disease, and this is more likely if the immune system is weakened.
There are two types of tests to determine whether people are carrying the TB bacteria. One is the TB skin test (also known as PPD), which requires the person to return to the clinic 2-3 days after the skin test is placed for the test to be interpreted. The other is a blood test called an interferon-gamma release assay (IGRA) (QuantiFERON and TSpotTB are two examples of IGRA blood tests).
If a person tests positive for carrying the TB bacteria in their body, tests are done to determine whether it is currently causing infection of the lungs (which is contagious). Anyone with active TB should get an effective combination of medications to be cured. If, however, there is no active infection, antibiotics can be used to prevent trouble in the future. In this setting antibiotics are given for 3-9 months.
If you got infected with HIV from unprotected sex, there is a chance you may have become infected with other sexually transmitted diseases, too. These include syphilis, gonorrhea, and chlamydia. Hepatitis B and hepatitis C can be sexually transmitted as well, particularly among men who have sex with men.
Infections of syphilis, gonorrhea, and chlamydia can occur in the throat, penis, vagina, and rectum. The bacteria that cause syphilis and gonorrhea can also spread through the blood to other parts of your body. Having one of these other diseases can make your HIV worse. They can also make you 2 to 5 times more likely to pass HIV along to a sexual partner. Syphilis, for example, can cause open sores on your genitals, which allows easy passage of HIV from you to your partner.
Tests for STDs, hepatitis B, and hepatitis C should be done at baseline. STD tests should be repeated at least once a year if you are sexually active and have had more than one sex partner since your last clinic visit. Men who have sex with men who have multiple or anonymous sex partners are recommended to be screened every 3-6 months, and this is a good idea for anyone with new partners.
Hepatitis A, B, and C
Your liver is an organ that processes almost everything you put into your body, including medications. Viruses can infect and irritate the liver causing damage, scarring, and possibly liver failure. The three most common viruses that can infect the liver are hepatitis A, hepatitis B, and hepatitis C.
- Hepatitis A virus (HAV): this virus is transmitted through contaminated food, water, or through the feces of someone who is infected. When you are diagnosed with HIV, your providers will check your blood to see whether you have protection from HAV either from previous infection or previous vaccination. If you have protection, great! There is nothing more to do. But if you do not, you may be offered the vaccine to prevent future infection.
- Hepatitis B virus (HBV): this virus is easily spread through contaminated blood and body fluids. When you are diagnosed with HIV, your providers will check your blood to see if you have either active infection, protection from infection, or no protection from HBV. If you have protection from infection, great! There is nothing else to do. If you do not have protection, you will be offered the HBV vaccine to protect from future infection. If HBV is found in your bloodstream (i.e. active infection), you will be offered medication that can kill both HBV and HIV.
- Hepatitis C virus (HCV): This virus is transmitted through contaminated blood. When you are diagnosed with HIV, your providers will check your blood to see if you have HCV. If so, you will be offered medication to cure your HCV. There is always risk of reinfection if re-exposed to the virus. Unfortunately, there is no vaccine for protection against HCV. For more information on hepatitis C, see HIV and HCV coinfection.
Just Diagnosed Resources
- Questions to Ask Your Provider about Your HIV Diagnosis
A list of questions to print out and bring to your medical appointment.
- Just Diagnosed with HIV?
The Body's starting place for people newly diagnosed with HIV. Articles on understanding HIV, first steps to treatment, telling others.
- The CDC National HIV Hotline, including its Spanish Service and TTY Service:
1-800-CDC-INFO (1-800-232-4636), 8 am - 8 pm ET, Monday through Friday.
- More Information:
- Find websites on more specific topics, such as opportunistic infections, travel health, and more.