Blood tests will become part of your life with cancer, so it's important that you understand what they're for. Various types of blood tests help diagnose your cancer. Sometimes, they are the first indicators of disease. Blood tests are also used to track the progression of your disease as well as help make decisions about your treatment.

Your doctor will often order a complete blood count (CBC). Your blood "counts" will be closely tracked throughout treatment.

Three primary types of blood cells are formed in your bone marrow: red cells, white cells, and platelets. Plasma is the liquid part of your blood in which the other cells travel. Certain kinds of cancer will affect the normal production of these cells. Some of the treatments you will receive, especially chemotherapy, will also affect your body's ability to produce blood cells. Here are some of the most important "counts" you will track:

Red Blood (RBC)

Your red cells are primarily responsible for carrying oxygen throughout your body.

Hemoglobin (Hgb)

Red cells contain hemoglobin, the molecule that carries oxygen and carbon dioxide in your blood throughout your body. If your hemoglobin is low, you will be anemic with symptoms like pale skin, shortness of breath, and fatigue. You may have low hemoglobin at diagnosis as well as during treatment because of your bone marrow's inability to produce new red cells.

Hematocrit (Hct)

Hematocrit refers to the volume of red blood cells in your system. (This is also called packed cell volume - PCV). Your hematocrit count is the ratio of red cells to plasma (the liquid part of your blood). It is expressed as a percentage. As an example, if your hematocrit is 30 it means that 30% of the blood that was drawn is red cells; the remaining 70% is plasma.

When you are on chemotherapy, your marrow's ability to make new red cells is decreased, so your hematocrit will go down. Because there is less oxygen in your body, you will feel tired and have little energy. If your hematocrit drops below about 18 percent, you will probably need a red blood transfusion. Your medical team will tell you the best thing to do.

White blood cells

Your white blood cells are responsible for fighting infection. Because cancer treatment affects your body's ability to produce white cells, your risk of infection becomes very high.

White Blood Cell Differential (DIFF)

The differential (or diff) refers to the distribution of different kinds of white cells in your blood. Each type of white cell will be listed as a percentage of the total. Neutrophils are the most important-infection fighting white cells. On your lab reports, the "differential" or "diff" will show the percentage of each type of white cell, all together equaling 100%. As an example:

Segmented neutrophils (or segs) 49%
Band neutrophils (or bands) 10%
Basophils 1%
Eosinophils 1%
Lymphocytes 29%
Monocytes 10%

Absolute neutrophil count (ANC)

This count is a measure of your body's ability to fight infection. It is the percent of neutrophils (segs + bands) multiplied by the total white blood count (WBC). The magic number is an ANC of 1,000 or more. When your ANC is less than 1,000, you are at very high risk for infection.

IMPORTANT:

If you have a fever higher than 38.5 C and your ANC is less 0 than 1,000, you will usually be admitted to the hospital to begin antibiotic treatment. Because the fever may be caused by a bacterial infection, extreme caution must be taken. Even if you feel perfectly fine, this precaution is necessary. Spending a few days in the hospital - just in case - is much better than taking a chance with a potentially life-taking infection.

Platelets

Platelets are the cells in your blood necessary to stop bleeding. Because chemotherapy affects your bone marrow's ability to produce platelets, you will probably need platelet transfusions during your treatment. Signs of low platelet count include:

• Bruising with no apparent cause
• Any unusual bleeding (nosebleeds, bleeding gums, vaginal or anal bleeding, prolonged bleeding from a cut)
• Petechiae (small red or purple spots on the skin)

Summary Chart

The following chart helps to summarize the important things to know about blood counts. Some labs use different measures to report results. Just be sure you are comparing apples to apples.

Blood Cultures

If your ANC (Absolute Neutrophil Count) is less than 1,000 and you develop a fever of more than 38.0 C, the risk of serious bacterial infection is high. You will probably be hospitalized and started on IV antibiotics. In order to know exactly what antibiotics best kill the bacteria, blood cultures might be drawn.

What this means is blood is drawn from your central line, and sent to the lab to see what type of bacteria grows in the culture medium (a substance that germs grow in). The most effective antibiotic to treat the specific bacteria can then be administered.