Bone Marrow Suppression
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 short-term 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 at times, 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 begin to drop. The type and dose of the chemotherapy will influence how low the blood cell counts will go and how long it will take for the bone marrow to recover.
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. Usually WBCs and platelets will reach their nadir within 7 to 14 days. Because RBCs live longer, they will typically take a few 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 probably be at their worst when the WBC, RBC, and platelets are at their lowest levels.
For information about low red blood cell counts, low white cell counts and low platelets, see the other sections of this document.