Understanding and Monitoring Your Blood Counts

Overview

A reduced number of blood cells in circulation is a common side effect of chemotherapy. Blood is composed of three basic blood cell types: red blood cells, white blood cells, and platelets. Blood cells are produced in the bone marrow and regularly released into circulation. Chemotherapy destroys rapidly dividing cells, a characteristic of cancer cells. However, bone marrow cells also divide rapidly and are frequently damaged by chemotherapy. Blood counts are monitored with a laboratory test called a Complete Blood Count (CBC). The best way to treat low blood counts is to prevent them before they occur. This can be accomplished with the administration of blood cell growth factors. In some circumstances, blood transfusions may also be necessary.

What are low blood counts?
What causes low blood counts?
What are the symptoms of low blood counts?
Why is it important to monitor low blood counts?
How are low blood counts diagnosed?
What are the treatments for low blood counts?

What are low blood counts?

A blood count is a measurement of the number of blood cells an individual has in circulation based on laboratory evaluation of a blood sample. Blood is composed of three basic blood cell types: red blood cells, white blood cells, and platelets. You should have billions of these blood cells circulating throughout your body. However, certain circumstances may cause you to have fewer cells than is considered normal, a condition which is called “low blood counts”. The laboratory test that is conducted to measure the number of blood cells is called a complete blood count, or CBC.

What causes low blood counts?

The most common reason cancer patients experience low blood counts is as a side effect of chemotherapy. Chemotherapy involves the use of drugs to destroy cancer cells. Chemotherapy works by destroying cells that grow rapidly, a characteristic of cancer cells. Unfortunately, chemotherapy also affects normal cells that grow rapidly, such as cells in the bone marrow that produce red blood cells, white blood cells, and platelets.

back to top

What are the symptoms of low blood counts?

Your symptoms will depend on which types of blood cells are low. Common symptoms of the different types of low blood cell counts are listed in table 1.

Table 1 Common symptoms of low blood counts

Why is it important to monitor blood counts?

It is important to monitor for low blood cell count because this condition may:

• Increase your risk of unpleasant and sometimes life-threatening side effects, such as fatigue, infection, and/or bleeding.
• Disrupt delivery of your cancer treatment, resulting in a change to the planned dose and time.

back to top

How are low blood counts diagnosed?

A test called the complete blood count (CBC) is used to determine whether your blood counts are low. The CBC measures the levels of the three basic blood cells: red, white, and platelets.

In the United States, the CBC is typically reported in the format shown below. If your blood counts fall outside of the normal range, which is shown in the “Reference interval” column, their values will be reported in the “Flag” column with an ‘L’ for low and an ‘H’ for high. The example CBC below shows that white blood cells, red blood cells, and platelets are all low.

Result column: The result column shows counts that fall within the normal range.

Flag column: The flag column shows counts that are lower ("L") or higher ("H") than the normal range.

Reference interval (or reference range) column: The reference interval shows the normal range for each measurement for the lab performing the test. Different labs may use different reference intervals.

White blood cells: White blood cells help protect individuals from infections. The above CBC report shows that the patient’s total white cell count is 1.5, which is lower than the normal range of 4.0-10.5. The low white cell count increases the risk of infection.

Differential: This portion of the CBC shows the counts for the 5 main kinds of white cells, either as percentages (the first 5 counts), or as the absolute number of cells (the second 5 counts).

Absolute neutrophil count: Neutrophils are the main white blood cell for fighting or preventing bacterial or fungal infections. In the CBC report, neutrophils may be referred to as polymorphonuclear cells (polys or PMNs) or neutrophils. The absolute neutrophil count (ANC) is a measure of the total number of neutrophils present in the blood. When the ANC is less than 1,000, the risk of infection increases. The ANC can be calculated by multiplying the total WBC by the percent of polymorphonuclear cells. For example, this patient's ANC is 0.34, which equals (WBC) 1.5 x 23%.

Red blood cells: Red blood cells carry oxygen from the lungs to the rest of the body. The above CBC report indicates that the patient has a red cell count of 3.5, which is lower than the normal range of 4.70-6.10, and therefore, shown in the flag column.

Hemoglobin (Hb or Hgb): Hemoglobin is a protein in the red cell that carries oxygen. The above CBC report indicates that the patient's Hb count is 10.8, which is below the normal range of 14.0-18.0. The hematocrit (HCT), another way of measuring the amount of Hb, is also low. This means that the patient has mild anemia and may be starting to notice symptoms.

These three ranges will vary depending on age and gender. For women, they will be lower than those shown here. For example, the Hb reference interval for a woman is 12.0-16.0.

Platelets: Platelets are the cells that form blood clots that stop bleeding. The above CBC report indicates that the platelet count for this patient is normal.

back to top

What are the treatments for low blood counts?

The best treatment for low blood counts is to prevent them before they occur. This can be accomplished with the administration of blood cell growth factors. Blood cell growth factors are substances produced by the body that stimulate the cells in the bone marrow to produce more red blood cells, white blood cells, or platelets. These factors have also been produced in a laboratory and are approved by the Food and Drug Administration (FDA) for the treatment of cancer patients with low blood counts.

Low red blood cell counts: Erythropoietin is a blood cell growth factor that selectively increases production of red blood cells. Clinical trials have demonstrated that erythropoietin is safe and effective in reversing anemia in cancer patients. Erythropoietin has been proven to effectively:

• Increase hematocrit
• Decrease the need for blood transfusions
• Reverse fatigue
• Improve overall sense of well-being

Erythropoietin is FDA-approved for the treatment of anemia in patients with nonmyeloid cancers (cancers that do not involve blood cells), whose anemia is a result of chemotherapy.

Treatment with erythropoietin causes a gradual increase in red blood cell production. The body uses iron in red blood cell production. Thus, supplemental iron may be required to adequately support erythropoietin-stimulated erythropoiesis. Virtually all patients receiving erythropoietin therapy will eventually require supplemental iron therapy.

Currently, there are two commercially available forms of erythropoietin for use in patients, epoetin alfa (Epogen® or Procrit®) and darbepoetin alfa (Aranesp® ). Both are manufactured in the same facility in the same manner. Epogen® and Procrit® have been in use for many years. Aranesp® is a unique, longer-acting form of erythropoietin and is more convenient because it allows patients to receive fewer injections than with Epogen® or Procrit®. The most common side effects seen in clinical trials with Aranesp® were fatigue, edema, nausea, vomiting, diarrhea, fever and shortness of breath. No important differences in side effects were seen between groups treated with Aranesp® and groups treated with the existing anemia treatment, Epogen®.

Low white blood cell count: The blood cell growth factors approved by the FDA for the prevention of chemotherapy-induced neutropenia are Neupogen® (filgrastim) and Neulasta® (pegfilgrastim). Multiple clinical trials have shown that Neulasta® and Neupogen® reduce the severity and duration of low white blood cell counts associated with many kinds of chemotherapy regimens. By increasing white blood cell counts, Neupogen® has been shown to decrease a patient’s risk of fever and admission to the hospital. The drawback of Neupogen®, however, is that it must be administered daily. In two clinical trials, a single dose of Neulasta® has been proven to be as effective as an average of 11 daily injections of Neupogen® for the management of neutropenia. The most common side effect you may experience with Neulasta® is aching in the bones. If this happens, it can usually be relieved with a non-aspirin pain reliever, such as acetaminophen. It is also possible to have an allergic reaction to Neulasta®.

Low platelet count: The blood cell growth factor approved by the FDA for the prevention of low platelet count is called Neumega®. Clinical studies have shown that Neumega® prevents thrombocytopenia and decreases the need for platelet transfusions in patients at high risk for developing a low platelet count. Neumega® has been reported to cause palpitations, fluid retention and diarrhea as well as other side effects in some patients.

Transfusions: In some cases, low blood counts may be so severe that you may need to undergo a blood transfusion. Red blood cells and platelets are often transfused. Sources for transfusional blood include blood banks or your own blood that you had stored for future use before undergoing treatment. Transfusions may be associated with complications, including allergic reactions that may range from mild to life-threatening. In general, it is better to prevent low blood counts than to treat them once they occur.

back to top

References

1. Glaspy JA, Jadeja J, Justice G. Optimizing the management of anemia in patients with cancer: a randomized, active-controlled study investigating the dosing of darbepoetin alfa [abstract]. Proceedings of the American Society of Clinical Oncology 38th annual meeting; May 18-21, 2002. Abstract 1446.

2. Kotasek D, Albertson M, Mackey J. Randomized, double-blind, placebo-controlled, dose- finding study of darbepoetin alfa administered once every 3 (Q3W) or 4 (Q4W) weeks in patients with solid tumors [abstract]. Proceedings of the American Society of Clinical Oncology 38th annual meeting; May 18-21, 2002. Abstract 1421.

3. Vose J, Crump M, Lazarus H. Randomized, multicenter, open-label study of pegfilgrastim compared with daily filgrastim after chemotherapy for lymphoma. Journal of Clinical Oncology. 2003;21: 514-519.

4. Green M, Koelbl H, Baselga J. A randomized double-blind multicenter phase III study of fixed-dose single-administration pegfilgrastim versus daily filgrastim in patients receiving myelosuppressive chemotherapy. Annals of Oncology. 2003:14:29-35.

back to top