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Understanding Low Red Blood Counts

Chemotherapy can cause low red blood cell counts. Understand the red blood cell tests, low red blood count symptoms, and what to do about them.

By , Caring.com senior editor
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Red blood cells are a key life force of the body, playing an essential role in carrying oxygen from the lungs to the cells. That's why when someone's red blood count drops, he really feels it -- and shows it. He may be pale, tired, weak, and have trouble catching his breath. Here's what you need to know to understand what's happening and what to do.

Why does cancer cause red blood cell (RBC) counts to drop?

  • In most cases, it's not the cancer itself but cancer treatment that leads to a shortage of red blood cells, also called anemia. Chemotherapy often damages the bone marrow that produces red and white blood cells and platelets, a condition called bone marrow suppression, or myelosuppression. As red blood cells die out, which they do naturally every 120 days or so, the body isn't able to replace them, and the red blood count drops.
  • Radiation therapy can also damage red blood cell production, particularly if the radiation targets areas such as the pelvis, where bones have more marrow and higher blood cell-generation activity.
  • Blood loss, either from surgery or from particular cancers, can also cause or exacerbate anemia. Colorectal cancers, for example, often cause blood loss as blood leaks from the intestines. Cancers that affect the blood and bone marrow, particularly lymphoma and leukemia, can also damage the production of red blood cells.

Tests and Prevention for Low Red Blood Cell Count

Why is there more than one test for red blood cell counts?

There are several ways that doctors commonly measure red blood counts:

  • Red blood cell count . This test counts the number of red blood cells in a single drop (a microliter) of blood. As a general guideline, consider the normal range to be 4.5 to 6.2 million for men; 4.2 to 5.4 million for women.
  • Hemoglobin . This test measures the red-pigmented protein that carries oxygen. Normal range for red blood count is 14 to 18 grams per deciliter in men; 12 to 16 grams per deciliter in women. When someone's hemoglobin drops below 10 grams per deciliter, he's considered anemic.
  • Hematocrit . This test measures the percentage of total blood volume made up of red blood cells. Normal range is 40 to 52 percent for men; 35 to 47 percent for women.

A complete red blood count usually includes additional measures of the size, capacity, and number of red blood cells. The doctor will usually order a battery of tests to get a complete picture of the health of a patient's red blood cells. For example, a low hematocrit in combination with low hemoglobin may indicate iron deficiency, while a high hematocrit can indicate dehydration.

Can I help prevent someone's red blood count from dropping?

There are medications called cell growth factors (also called colony stimulating factors) that can be given along with chemo or radiation to prevent red blood counts from dropping. The growth factor that boosts production of red blood cells is epoetin or darbepoetin (brand names Procrit, Epogen, Aranesp). Growth factors can take between two and eight weeks to work, so they're not a solution for dramatic red blood cell loss. There's also a risk of side effects, so a patient's doctor will decide whether to prescribe cell growth factors based on her assessment of the patient's risk of developing a low red blood count.

Get as much information as you can from the doctor about the chemo regimen of the person you're caring for and the effect you can expect it to have on his red blood count. "Some drugs reduce the red blood cell count by 25 percent immediately; some drugs take a week before the count start to drop. Every drug and regimen is different," says Terry Anders, an oncology nurse at the Zangmeister Cancer Center in Columbus, Ohio. Because side effects include fluid retention and heart palpitations -- both of which can worsen heart conditions -- the doctor will take into account whether the patient has heart problems when deciding whether to prescribe Procrit or other growth factors. Other side effects include diarrhea, vomiting, fever, and upper respiratory infection. In addition, Procrit can cause shortness of breath and edema, so if the person you're caring for already has these problems, the doctor may be conservative about prescribing it.

Low Red Blood Cell Count Symptoms, Treatment, and Recovery

What are the symptoms of low red blood count?

The typical signs of anemia are extreme fatigue and shortness of breath, but a low red blood count can cause a host of different symptoms. A patient's skin may be pale or clammy, or he may have a rapid heart rate, chest pain, or difficulty staying warm. Because low oxygen in the blood can affect the brain as well, he may feel dizzy and light-headed or have difficulty concentrating or remembering things. He may also have headaches.

How low does someone's red blood count need to go before the doctor recommends treatment?

This is a very individual decision, and the doctor will make it based more on symptoms (such as fatigue or shortness of breath) than on a particular number. It's likely the doctor will take a wait-and-watch attitude for as long as possible before recommending medication or a transfusion, because he's hoping the red blood count will rise on its own. Also, keep in mind that red blood count won't drop dramatically right after chemo; it usually takes one to two weeks for the blood count to reach what doctors call the nadir, the point at which it drops to its lowest point. Cutoff rates vary according to different labs, but if a patient's hemoglobin drops below eight, most doctors will recommend either growth factors or a transfusion.

How long does it take for the red blood count to rise again?

Red blood cells have a long life -- up to 120 days -- so rebuilding someone's red blood count is a long, slow process. The speed with which bone marrow makes new red blood cells is also affected by factors such as the type of cancer, type of treatment -- particularly the type and dosage of chemo -- and the patient's general state of health.

One thing to keep in mind is that red blood counts won't drop immediately after chemo but will start dropping after a week or two, and will then continue to fall for several more weeks. This is because chemo doesn't kill off the red blood cells already in the bloodstream, which are mature and aren't dividing rapidly. It kills off the cells forming in the marrow, and therefore there's a delayed response that corresponds with the rate at which the marrow is creating new cells. The rate of regeneration can be affected by the patient's age and overall health. Also, some types of cancer and some types of treatment (such as radiation and some medications) suppress the production of red blood cells, so the rebuilding process can be much slower.