The bone marrow is the thick liquid in the inner part of some bones that produces white blood cells (WBCs), red blood cells (RBCs), and platelets. One of the most common side effects of chemotherapy is damage to the bone marrow.
Cells are constantly produced and grow rapidly in the bone marrow. As a result, they are sensitive to the effects of chemotherapy. Until your bone marrow cells recover from chemotherapy damage, you may have abnormally low numbers of WBCs, RBCs, and/or platelets. This is called bone marrow suppression or myelosuppression.
While you are getting chemotherapy your blood will be tested regularly, even daily when necessary, so the numbers of these cells can be counted. This test is often called a complete blood count (CBC). If you are being treated for leukemia, bone marrow samples may also be taken periodically to check on the blood-forming marrow cells that develop into WBCs, RBCs, and platelets.
The decrease in blood cell counts does not occur right at the start of chemotherapy because the drugs do not destroy the cells already in the bloodstream (these are not dividing rapidly). Instead, the drugs affect new blood cells that are being made by the bone marrow.
As blood cells normally wear out, they are constantly replaced by the bone marrow. Following chemotherapy, as these cells wear out, they are not replaced as they would be normally, and the blood cell counts will begin to drop. The type and dose of the chemotherapy will influence how low the blood cell counts will drop and how long it will take for the drop to occur.
Each type of blood cell has a different life span:
- WBCs come in several types that have a wide range of life spans. Neutrophils, a type of white blood cell of special importance in fighting infections live for an average of 6 hours
- Platelets average 10 days
- RBCs average 120 days
The lowest count that blood cell levels fall to after chemotherapy is called the nadir. The nadir for each blood cell type will occur at different times, but usually WBCs and platelets will reach their nadir within 7 to 14 days. Because RBCs live longer, they will typically take several weeks to reach their nadir. Within 3 or 4 weeks after treatment, the blood counts improve and start to approach normal levels.
Knowing what these 3 types of blood cells normally do can help you understand the effects of low blood cell counts.
- WBCs help the body fight off infections.
- Platelets help prevent bleeding by forming plugs to seal up damaged blood vessels.
- RBCs bring oxygen to cells throughout the body so they can turn certain nutrients into energy.
The side effects caused by low blood cell counts will likely be at their worst when the WBC, RBC, and platelets are at their lowest levels.
Low white blood cell counts: The medical term for a low WBC count is leukopenia. Blood normally has between 4,000 and 10,000 WBCs per cubic millimeter (mm3). WBCs are divided into 2 main categories, based on how they look under the microscope:
- Granulocytes, which contain granules (visible specks) in the cytoplasm of the cell. This category includes 3 subtypes -- neutrophils, eosinophils, and basophils.
- Agranulocytes, which do not contain granules in the cytoplasm of the cell. This category includes 3 subtypes -- lymphocytes, monocytes, and macrophages.
Granulocytes, especially neutrophils, provide an important defense against infections and are the most numerous type of WBC. Neutropenia, an abnormally low number of neutrophils, is the most common side effect that puts people with cancer at risk for infection. To determine how likely someone is to develop an infection, health care providers look at the number of neutrophils in the blood, called the absolute neutrophil count (ANC). The normal range of neutrophils is generally between 2,500 and 6,000 cells per cubic millimeter. The lower the ANC, the less able the person is to fight off infection. Someone is neutropenic when their ANC is 1,000 or less. An ANC lower than 500 is considered severe neutropenia.
A person who is neutropenic has a high risk of developing an infection. Infections in neutropenic patients are very serious and can quickly become life threatening. Your doctor will likely watch your neutrophil count closely during chemotherapy.
Having a low WBC count or neutrophil count does not mean you will definitely get an infection. But you need to watch for these signs and symptoms:
- Sore throat
- New cough or shortness of breath
- Nasal congestion (stuffy nose)
- Burning during urination
- Shaking chills
- Redness, swelling, pain, and warmth at the site of an injury or at an IV, CVC, or implanted catheter site
Fever is a very important sign and is often the first sign of an infection. Usually you will be instructed to call your doctor or nurse if you have a fever higher than or equal to 100.5°F when taken by mouth, or if you have any other signs or symptoms of infection (such as those listed above).
Your health care team may take measures to lower your risk of infection. You may be told to stay away from small children or other people who are likely to be sick. When WBC counts are very low, doctors often prescribe antibiotics as a preventive measure. These anti-infection drugs may be given intravenously, but are most often given by mouth.
Because of the risk of infections, further chemotherapy doses may need to be delayed when you have a very low WBC count.
In some situations, doctors may prescribe growth factors (also called colony stimulating factors) to keep the WBCs from falling too low so that chemotherapy can be given on schedule. (As previously discussed, the timing of the chemotherapy cycle is important in killing the maximum number of cancer cells.) Your body normally produces several growth factors to prompt the bone marrow to make various types of blood cells. But the normal levels of these factors in the body are often not enough to keep up with demands during chemotherapy. Researchers have learned how to make these growth factors in the lab, and they are now available as drugs which help the body maintain normal blood cell levels.
The growth factors that stimulate production of WBCs are granulocyte-macrophage colony-stimulating factor (GM-CSF, also called sargramostim or Leukine®) and granulocyte colony-stimulating factor (G-CSF, also called filgrastim or Neupogen®). These drugs are often given daily, usually starting the day after you receive chemotherapy. They can be given for up to 2 weeks. A newer, longer lasting form of G-CSF (pegfilgrastim or Neulasta®) is now available and is given only once each chemotherapy cycle, usually 24 hours after completing chemotherapy.
These drugs help bone marrow recover more quickly and reduce your risk of getting a serious infection. They are commonly given as injections under the skin (SQ). Nurses give the injections if you are in the hospital or at the doctor’s office, but you or your family members can learn how to give these injections at home.
You can learn more about this in our document, Infections in People with Cancer.
Low red blood cell counts: Not having enough RBCs is called anemia. Doctors use 2 measurements to determine if you have enough RBCs.
- The red pigment in RBCs that carries oxygen is hemoglobin. If there are not enough RBCs, the blood hemoglobin concentration will be less than its usual range of 12 to 16 grams per deciliter (g/dL) in women or 14 to 18 g/dL in men.
- Hematocrit is the percentage of total blood volume occupied by RBCs. Its normal range is between 37% and 52%. Levels are normally higher for men than for women.
With anemia, you may have the following symptoms:
- Extreme tiredness called fatigue (described below)
- Pallor or paleness of the skin and mucous membranes (like the mouth and gums)
- Shortness of breath, especially with exertion (walking, going up steps, etc.)
- Low blood pressure
- A rise in heart rate or breathing rate (or both)
Anemia caused by chemotherapy is usually temporary. But blood loss caused by surgery or by the cancer (a common occurrence with colorectal cancers, for example) can make anemia even worse.
If the symptoms are severe, blood transfusions can temporarily correct the RBC levels until the bone marrow is healthy enough to replace worn-out RBCs. Because blood transfusions have some risks, doctors use this procedure only if there are serious signs and symptoms, such as severe shortness of breath and/or very low RBC counts (typically less than 8 g/dL). Other factors will also affect this decision. For example, people with heart or lung diseases are more sensitive to anemia and may have severe symptoms even though their hemoglobin levels may be higher than 8 g/dL.
An option for treating anemia caused by chemotherapy is a drug called erythropoietin (also called EPO, epoetin, Procrit®, or Epogen®). This drug is only used in patients whose treatment is not expected to cure their cancer. It is a man-made version of a naturally-occurring growth factor that prompts bone marrow cells to make more RBCs. It can relieve symptoms of anemia and reduce the need for blood transfusions, but it usually takes at least 2 weeks to start working. Procrit is generally given once a week by injection under the skin (SQ) until the hemoglobin level rises to an acceptable level (usually between 10 and 12 g/dL). A newer, longer lasting form, known as darbepoetin (Aranesp®), is given weekly, but can be given every 2 to 3 weeks in some patients.
Because these growth factors may raise the risk of blood clots, blood counts must be watched closely at follow-up appointments. If you notice shortness of breath getting worse, pain or swelling in your legs, dizziness or fainting, higher blood pressure readings, or fatigue, call your doctor right away.
Red blood cell growth stimulators were often used in the past to help patients avoid transfusions. Studies are now suggesting that these drugs may cause some cancers to grow. They may even lead to earlier deaths in some people. These effects were seen in studies that used these drugs to bring the hemoglobin up to normal (higher than 12). Earlier studies had not aimed to get the hemoglobin that high. Because of these concerns, the FDA has warned against using this type of drug to get a high target hemoglobin. The FDA also decided that people whose chemotherapy is expected to cure their cancer shouldn't get these drugs at all.
More information is available in, Anemia in People with Cancer, another American Cancer Society document.
Low platelet counts: The normal range for platelet counts is between 150,000 and 450,000 per cubic millimeter (mm3), although this varies somewhat depending on the lab. The medical term for a low platelet count is thrombocytopenia.
If your platelet count is low, you may:
- Bruise easily
- Bleed longer than usual after minor cuts or scrapes
- Have bleeding gums or nose bleeds
- Develop petechiae (small reddish-purple spots on your skin)
- Have headaches
- Have visible blood in stool or urine
- Have serious internal bleeding if the platelet count is very low
Although low platelet counts resulting from chemotherapy are temporary, they can cause serious blood loss. This, in turn, can lead to damage in internal organs.
Sometimes a low platelet count will delay necessary surgery because doctors are concerned about blood loss during surgery.
If platelet counts are very low (below 10,000) or if a person with moderately low counts is bleeding or bruising too easily, platelet transfusions may be given. Transfused platelets last only a few days and must often be repeated. Some people who have received many platelet transfusions can develop an immune reaction that destroys donor platelets.
A platelet growth factor called oprelvekin (Neumega®) is a drug that is sometimes given to people with severe thrombocytopenia. This can lower their need for platelet transfusions and can lessen the risk of bleeding. The drug is given as an injection under the skin (SQ) every day.