Understanding HIV-Related Lab Tests I: Complete Blood Count and Blood Chemistry

Table of Contents

• Lab Tests Are Important Tools
• The Basics
• Complete Blood Count (CBC)
• Blood Chemistry (Chemistry or Chem Screens)
• The Bottom Line

Lab Tests Are Important Tools

Having regular lab tests is a necessary part of caring for your health. If you are living with HIV (HIV+), lab tests are especially important tools that help you and your health care provider keep track of how you are doing in the following areas:

Immune System Status

• How HIV is affecting your immune system
• If you need to start or switch HIV drugs
• Example of lab test: CD4 cell count test (see our info sheet on Understanding CD4 Cells and CD4 Cell Tests)

HIV Illness

• How HIV is responding to the drugs you are taking
• Which drugs to use
• The specific characteristics of your virus
• Examples of lab tests: viral load test, resistance test, tropism test (see our info sheet on Understanding Lab Tests II)

Overall Health

• How your body's organ systems are functioning
• If you have side effects from the drugs
• If you are having problems that are not related to HIV
• Examples of lab tests: complete blood count, blood chemistry (explained below)

The Basics

When you are first diagnosed as HIV+ and when you first start taking HIV drugs, you should get "baseline" tests that give a picture of your health at that moment. Later tests can be compared against these results to see how things are going, and if they are changing. Most lab tests should be done every three to six months, or as often as your health care provider recommends.

Because different labs use different equipment, test results from different labs can vary. Therefore, it is a good idea to have your tests done at the same lab each time. If you get an unexpected result on one test, your health care provider will probably want you to get a second test to see if the results are the same as the first one. Try not to worry too much about a single unexpected result -- usually trends over time are more important.

Most lab reports show the normal range of results from each test and highlight any of your results that are outside the normal range. The ranges listed below are general and may not be exactly the same as your lab. Look at your lab report for the normal ranges they use.

Complete Blood Count (CBC)

Blood is made up of different types of cells including red blood cells, white blood cells, and platelets. The complete blood count (CBC) is a test that measures the amount of these cells in a sample of your blood. CBCs are especially important for HIV+ people because some HIV drugs and infections can cause changes in your red or white blood cell counts.

• Red blood cells (erythrocytes)
  Red blood cells (RBCs) carry oxygen throughout the body. A typical RBC count for women is four to five million red blood cells. Hematocrit (HCT) measures how much of your blood is made up of RBCs, and hemoglobin (HGB) tests measure the amount of hemoglobin in your blood. Hemoglobin is the protein in RBCs that allows them to carry oxygen. A normal HCT for women is 36 to 44 percent and a normal HGB level is 12 to 15. A low RBC count, HCT, or HGB may mean you have anemia, which can cause you to feel tired. For more information, see our Anemia and Women info sheet.
• White blood cells (leukocytes)
  White blood cells (WBCs) are produced by the immune system and help defend the body against infection. A normal total WBC count is 4,500 to 10,000. A high count may mean that your body is fighting an infection. Low counts may be caused by certain drugs or infections. There are different types of white blood cells that are listed on your lab report as "the differential." The differential tells you the amount of each type of white blood cell as a percentage of the total WBC count.
  • Neutrophils
    These cells fight bacterial infections. A normal neutrophil percentage is about 50 to70 percent of the total WBC count. When your neutrophil count is low (a condition called neutropenia), you are more likely to get bacterial infections.
  • Lymphocytes
    There are two types of lymphocytes: B cells and T cells. B cells make antibodies and T cells attack germs. Usually, lymphocytes account for about 20 to 40 percent of the total number of WBCs. CD4 cells are a type of T cell that is measured separately. For more information, see our sheet on Understanding CD4 Cells and CD4 Cell Tests.
  • Monocytes and Macrophages
    These cells engulf or "eat" and destroy disease-causing organisms (germs). They normally make up about two to ten percent of the total WBC count.
  • Eosinophils and Basophils
    These cells play a role in allergic reactions and defend against parasites. They normally make up about one to eight percent of the total WBC count.
• Platelets (thrombocytes)
  Platelets are necessary for blood clotting. A normal platelet count is about 130,000 to 440,000. If your platelet count is low, you may bleed or bruise easily.