|Understanding Laboratory Tests|
| CD4 count (or T-cell count)|
The CD4 count is like a snapshot of how well your immune system is functioning. CD4 cells (also known as CD4+ T cells) are white blood cells that fight infection. The more you have, the better. These are the cells that HIV kills. As HIV infection progresses, the number of these cells declines. When the CD4 count drops below 200 due to advanced HIV disease, a person is diagnosed with AIDS. A normal range for CD4 cells is between 600 and 1,500. Usually, when a person with low CD4 cells starts HIV medicines, the CD4 cell count increases as the HIV virus is controlled. Most but not all people will experience an increase in CD4 cell with effective HIV treatment.
The higher your CD4 count, the better.
The same test that measures your CD4 count usually includes a CD8 cell count, too. CD8 cells (also known as CD8+ T cells) are another type of white blood cell that seek out and destroy cells infected with viruses, including HIV-infected cells.
| Viral load (or 'HIV RNA')|
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 viral load as much as possible for as long as possible, and for most patients, the goal of HIV treatment is an HIV viral low that is "undetectable," meaning that the HIV RNA is below the detection limit of the test. The lower limit of HIV RNA detection depends on the test used, some go down to 75 copies/ml, while other go as low as 20. High levels--from 30,000 (in women) to 60,000 (in men) and above--are linked to faster disease progression.
Unlike many other infection where treatment can lead to a cure, we know that with current HIV treatment, even if HIV levels are undectable, the 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 viral load tests are usually done when you first see a new provider and every 3 months when HIV treatment is started.
| Resistance test (HIV genotype)|
This test determines whether the particular virus in your body is resistant to anti-HIV medications.
HIV reproduces rapidly and, as the virus makes copies of itself, little changes (or mutations) sometimes result. These changes can lead to different HIV strains, particularly if the person is taking 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.
A person can be infected with a drug resistance strain of HIV even if they have never taken HIV medicines. For this reason, an HIV resistance test is recommended for all HIV infected people as soon as they are diagnosed.
| Complete blood count (CBC)|
This test looks at the different cells in your blood, including red blood cells, platelets, and white blood cells.
|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 lead to fatigue. Tests looking at your red blood cells include red blood cell count, hemoglobin, and hematocrit.|
|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.|
|White blood cells come in many types, and all are involved in your immune system's effort to keep you healthy. High white blood cell counts may indicate that you are fighting an infection. Low counts may put you at risk of getting an infection.|
These tests are usually done every 6 to 12 months, unless your lab values are fluctuating a lot, or you have symptoms of infections associated with HIV disease. Then the tests are done more often, every 3 to 6 months.
| 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, magnesium, 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 are viral hepatitis, alcohol, medications, and street drugs.) These tests measure alkaline phosphatase, ALT, AST, albumin, and bilirubin. It is important to have a baseline measure of your liver health, because you may need to take HIV medications in the future, and some of these medications can cause liver damage.|
Blood chemistry tests are usually done a couple of times a year.
| TB test|
TB is short for tuberculosis, a disease that people with HIV are at higher risk for getting. Most people who are exposed to TB don't get sick--the bacteria can live in the body for a long time without causing disease. You can be tested for exposure to TB with several different tests. One is the TB skin test (also known as PPD), which requires a return visit 2-3 days after the skin test is placed for an interpretation. There are also blood tests for tuberculosis called interferon gamma release assays (QuantiFERON and TSpotTB are two kinds of these blood tests)
HIV can make both of these tests less reliable, particularly if the immune system is weakened. Neither of these tests can tell the difference between exposure to TB (a person is not sick with TB) and active TB (where a person is sick with TB). If a person has been exposed to TB, treatment can reduce the risk of becoming sick with TB in the future.
| STD screening|
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 gonorrhea, syphilis, and chlamydia. Hepatitis C is increasingly recognized as a sexually transmitted disease as well, particularly among men who have sex with men
The bacteria that cause these diseases can be found in the throat, penis, vagina, and rectum. The bacteria that cause syphilis are also found in the blood. Having one of these other diseases can make your HIV advance faster. 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.
| Hepatitis A, B, and C|
Your liver is an organ that processes almost everything you put into your body, including drugs. The three most common types of viral hepatitis (A, B, and C) can damage your liver.
Some of the same behaviors that put people at risk for HIV (unprotected sex, injection drug use) can put them at risk for hepatitis.
If you have both HIV and hepatitis B or C, your treatments for either disease can be affected. If you have HIV, your hepatitis may progress faster. If your liver is damaged from hepatitis, it may be harder for your body to process your HIV medications.
What's more, some HIV treatments can damage your liver, so if you have hepatitis, your doctor may want you to try other treatments.