Understanding Your Lab Test Results

When you have cancer it seems that someone is always taking blood for some kind of test. Lab tests can show small changes before you notice any problems. They are done to help watch your body’s response to treatment. Your doctor can take action as soon as your blood counts change to help prevent many side effects.

Here we will talk about some of the most common types of blood tests and what they can tell the doctor about your health.

Complete blood count (CBC)

The most common lab test that you will have done during treatment is called a complete blood count, or CBC. Blood is made up of water, proteins, nutrients, and living cells. A CBC tells your health care team about the cells in your blood. It measures 3 basic types of blood cells:

• Red blood cells
• White blood cells
• Platelets

Each of these cells has a special purpose. And each can be harmed by cancer and cancer treatments.

Red blood cells (RBCs)

RBCs carry oxygen to and carbon dioxide away from the cells in your body. The CBC measures red blood cells in many ways, but the simplest measure is either

Hemoglobin (Hgb), the part of each RBC that carries iron

or

Hematocrit (Hct), the percent of RBCs in the blood

When the Hgb and Hct values fall too low, it is called anemia (uh-nee-me-uh).

Platelets (Plts)

Platelets help control bleeding. You may bruise or bleed easily when your platelet levels are low. The risk of bleeding goes up when platelet levels drop below 20,000.

When the platelet count is low, your health care team may call it thrombocytopenia (throm-bo-sy-tuh-PEEN-e-uh).

White blood cells (WBCs)

WBCs fight infection. There are many types of white blood cells and each fights infection in a special way.

The most important infection-fighting WBC is the neutrophil (new-truh-fil). The number doctors look at is called your absolute neutrophil count (ANC). A healthy person has an ANC between 2,500 and 6,000.

The ANC is found by multiplying the WBC count by the percent of neutrophils in the blood. For instance, if the WBC count is 8,000 and 50% of the WBCs are neutrophils, the ANC is 4,000 (8,000 × 0.50 = 4,000).

When the ANC drops below 1,000 it is called neutropenia (new-truh-peen-e-uh). Your doctor will watch your ANC closely because the risk of infection is much higher when the ANC is below 500.

Chemistry panel

Another type of blood testing looks at blood chemistry. Chemistry panels may also be called by other names (such as metabolic profile, or blood chemistry profile). One blood sample can be used to measure many things like:

• Fats (lipids)
• Proteins
• Sugar (glucose)
• Electrolytes (elements like potassium, magnesium, and calcium)
• Enzymes

Certain blood chemistry tests can show how well your organs are working. For instance, liver function studies tell your doctor how well your liver is working. Other tests look at how well your kidneys are working. The chemistry panel may also show other problems with body function.

Some treatments can cause changes in the levels of your body’s blood chemistry, such as a drop in the amount of potassium in your blood. Your blood chemistry balance can also be changed by dehydration (not enough fluid in the body), which may be caused by nausea, vomiting, or diarrhea. Your doctor will order blood chemistry tests if he or she is concerned that you may have any of these problems.

If the tests show that certain electrolytes are too low, your doctor may decide to replace them. If the tests show you are dehydrated, you may be given intravenous (IV) fluids. It’s important to have all the tests your doctor orders because most of the time you will not have any symptoms until one or more blood chemistry values are dangerously low or high.

How to find normal values

Each lab has its own range for what it considers normal values for complete blood counts and chemistry panel results. What’s normal for one lab might not be normal for another, so it’s important to know what your lab’s normal range is when looking at your results. Normal ranges for some tests also vary by age and gender. As a rule, the normal ranges are written on the lab report, next to your test results.

Some people find it helpful to ask for a copy of their results and have a member of their health care team go over the numbers with them.

Common terms and numbers you may see on a CBC report and what they mean are on this chart:

*Note that results are often given in short form, as shown on this table; for instance, a WBC result may be shown as 6.2 rather than 6,200, which is why the Units column shows multiplying by 1000 (X 1000). RBCs are often shown as multiples of a million.

^# These number ranges vary among labs.

If you have questions about your lab tests or need cancer-related information or support, please call us any time, day or night, at 1-800-227-2345 or visit us online at www.cancer org.