What Happens During the Stem Cell Transplant Process?

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Stem Cell Transplantation Program


The first part of the stem cell transplant process is called conditioning. During this time, you'll receive chemotherapy and/or radiation therapy to damage and possibly destroy your bone marrow.

The stem cell transplant itself replaces the damaged bone marrow with healthy stem cells. You can think of stem cell transplantation as a transfusion of blood and immune cells rather than a surgical procedure.

If your bone marrow were not replenished after very high doses of treatment, your blood counts would not recover for at least several months — or perhaps not at all. With a boost from a stem cell transplant, your blood counts should return to safe levels in two to six weeks.

What is chemotherapy?

Chemotherapy is a treatment with anti-cancer drugs that disrupts cancer cells’ ability to grow and multiply in your body. The goal of treatment is to kill as many cancer cells as possible.

However, chemotherapy can also affect non-cancerous cells. The normal cells typically affected by chemotherapy include bone marrow, hair follicles, and cells of the gastrointestinal and reproductive systems.

What is radiation therapy?

Radiation therapy uses high-energy X-rays or beams to kill or stop cancer cells from growing and dividing. Radiation is often given in combination with chemotherapy.

What is total body irradiation?

Some stem cell transplant patients receive total body irradiation treatment. Unlike radiation that targets a specific area of the body, total body irradiation treats the entire body with radiation to kill the cancer cells and suppress the immune system.

How Do Chemotherapy and Radiation Affect My Blood Cells?

Because cancer cells tend to grow at a faster rate than other cells in your body, chemotherapy affects cells that grow quickly more than cells that grow slowly.

However, some normal cells also have a fast rate of growth, including blood cells. A side effect of chemotherapy is that it may kill young blood cells as they are growing. It can take anywhere from three to ten days for your blood cell count to fall to its lowest point.

When radiation is used to prepare you for stem cell transplant, it targets cancer cells and also suppresses your immune system.

Your blood will be tested to see how many of each type of blood cell you have. This is called having your “counts” checked. While you are in the hospital, your counts are checked daily. Your nurse or doctor will tell you when your blood counts are expected to be low. The time when your white blood cell and platelet counts are at the lowest is called your nadir.

It is important for you to understand how your counts can affect your treatment, activity level, and infection exposure.

Learn what precautions you should take when your blood counts are low 

White Blood Cells

White blood cells are responsible for fighting infection. Your normal white blood cell count is 4,000 to 10,000.

There are three main types of white blood cells: neutrophils, lymphocytes, and monocytes. Neutrophils, the most important infection-fighting cells, consist of "polys" and bands. The total number of polys and bands is referred to as the absolute neutrophil count (ANC).

What happens when my counts are low?

When your ANC drops below 500 — a condition called neutropenia — you are at greater risk for infection. Your doctor may prescribe a colony-stimulating factor called G-CSF or GM-CSF to stimulate the production of cells in your bone marrow and help your white blood cell count recover more rapidly.

When your ANC recovers, your risk of infection declines, but you may still be at risk for viruses and fungi. It may take as long as one to two years before your immune system recovers completely.

Calculating Your Absolute Neutrophil Count (ANC)

You can calculate your ANC by taking the total number of white blood cells and multiplying it by the percentage of polys.

2,500 WBC count X .50 Poly count = 1,250 (no neutropenia)
1,250 WBC count X .20 Poly count = 250 (neutropenia)

Red Blood Cells

Red blood cells are responsible for carrying oxygen to cells throughout your body. Red blood cells are measured by values called hemoglobin (Hgb) and hematocrit (Hct). The normal value for hemoglobin is 14.0 to 18.0. The normal value for hematocrit is 37 to 52.

If your red blood cell count is too low, this is called anemia. You may feel more tired or short of breath than usual. Sometimes your red blood cells may be low because of the disease itself, or as a result of the treatments you are receiving.

If your red blood cell count is low, your care team may decide that you need a blood transfusion.


Platelets help your blood to clot so that you stop bleeding if you get a cut or a bruise. The normal platelet count is between 150,000 and 400,000.

If your platelet count drops below 50,000, you are at higher risk of bleeding, although the risk is low until the count gets down to 21,000.

A low platelet count is called thrombocytopenia. Depending on your clinical circumstances, you may or may not receive a transfusion in response to a low platelet count.

Your platelet count will determine when physical therapy (or what level of exercise) is appropriate for you during the different stages of the transplant process.