Mark Oren, M.D., FACP
A complete blood count (CBC) is a test that measures the levels of red blood cells(RBC), white blood cells(WBC) and platelets in a person’s blood. A CBC is one of the most common blood tests performed today. It can provide important information on the types of blood cells present, their condition, number and percentage in relation to other cells. The results of a CBC can help diagnose many conditions and diseases.
For instance, high WBC levels may indicate a heart attack, infection, an inflammatory disease or leukemia. In contrast, low levels can be caused by kidney or liver disease, radiation exposure or the presence of a toxic substance in the body.
High RBC levels may indicate a lack of fluid in the body (dehydration), exposure to high altitude or some primary blood diseases, whereas low levels are usually an indicator of anemia. Anemia may be a sign of several cancers including colorectal, stomach and lymphomas.
High platelet levels may be due to severe bleeding, infection, strenuous exercise, pregnancy or other factors. An indvidual who has low platelet levels may have been affected by an infection or a lack of either folic acid or vitamin B–12. Certain primary benign blood diseases or blood cancers can also cause high or low levels.
CBC is typically performed on cancer patients undergoing chemotherapy or radiation therapy to determine if the treatments have affected bone marrow cell production. In addition, a CBC can help detect diseases such as leukemia or multiple myeloma.
Some medications may affect the results of a CBC. Patients are urged to carefully follow their physician’s orders about how to take their medications before the test in order to ensure its accuracy. There is no need to stop eating or drinking before undergoing a CBC.
CBC tests can be performed in a number of different settings, including a physician’s office, hospital, laboratory or outpatient clinic. They are relatively quick, performed with little pain and can yield valuable information about an individual’s health.
About CBC and cancer
A complete blood count (CBC) includes counts of all three types of blood cells present in a blood sample – red blood cells (RBC), white blood cells (WBC) and platelets (thrombocytes). The CBC can provide important information about the types of blood cells present, their condition, number and percentage in relation to other cells. A CBC can be used to:
- Obtain a picture of the patient’s general health status
- Detect anemia, which can be a sign of mild and serious conditions, including colorectal, kidney, or stomach cancers and lymphomas
- Rule out certain diseases or deficiencies
- Estimate fluid levels
- Diagnose a disease, allergy, abnormal condition inflammation or infection
- Follow and manage a patient’s treatment
- Determine the severity of a blood loss
- Investigate abnormal bleeding or clotting disorders
Blood cell counts also may be performed to check for side effects in cancer patients receiving chemotherapy or radiation therapy. These treatments can destroy bone marrow, which produces stem cells that develop into white blood cells and red blood cells. CBC testing can reveal if these levels are abnormal, and whether or not patients might need growth factors to help their bone marrow produce new blood cells.
CBC tests may be performed for a number of reasons, including:
- As part of a diagnostic workup
- During a routine physical examination
- To diagnose diseases of the blood, including leukemia and multiple myeloma
- To monitor a patient’s response to drug or radiation therapy or chemotherapy
- To detect cancer that has metastasized to bone marrow
- To determine whether a patient can tolerate invasive procedures such as biopsy
- Before surgery or other specialized treatments
- To monitor a patient’s progress during treatment
A CBC can be performed in medical settings, such as a physician’s office, hospital, laboratory or outpatient clinic. In addition to routine testing, a CBC may be administered if an individual demonstrates specific signs and symptoms. These include:
- Sudden and increasing fatigue when engaging in regular activities
- Chest pain or shortness of breath
- Blood in stool as indicated by bright red, dark red or black stools
- Vomiting that includes dark brown or bright red material
- Pale or yellowing skin
- Sudden redness, bruising or swelling of the skin
- Sudden cough or shortness of breath
- Sudden abdominal pain
- Burning during urination
- Sore throat or mouth sores
- Temperature of more than 100.5 degrees Fahrenheit (38 degrees Celsius) when taken orally
- Red rash that looks like pinpoint dots, usually on feet and legs
- Bad headaches or dizziness
- Joint or muscle pain
Complete blood count testing comes with very few serious risks. Some of the potential risks involved in the testing include:
- Excessive bleeding
- Fainting or lightheadedness
- Blood accumulating under the skin (hematoma)
- Multiple punctures to locate veins
- Inflammation of the vein (phlebitis)
Types and differences of CBC
The CBC includes the following tests:
- Red blood cell tests
- Red blood cell count
- Size and shape
- White blood cell tests
- White blood cell count
- Differential count (kinds of white blood cells present and whether the cells have a normal appearance)
- Platelet tests
- Platelet count
Red blood cell tests
A major test of the red blood cells is the red blood cell (RBC or erythrocyte) count. This test counts the number of red blood cells within a specific amount (usually a cubic millimeter) of blood. The normal range may vary slightly from lab to lab but it usually falls between 4.2 and 5.9 million cells per cubic millimeter of blood. Infants and people who live at high altitudes will have slightly higher counts. Erythrocytosis (an excess of RBCs) can occur for many reasons. One of the more serious causes is kidney cancer.
Hematocrit (Hct) refers to the percentage of blood consisting of red blood cells. Hematocrit (meaning “to separate blood”) is an indicator of both the number and the size of red blood cells. A hematocrit of 45 would mean that red blood cells compose 45 percent of a blood sample. The normal range for hematocrit varies slightly between the sexes with a range of 45 to 52 percent for men and 37 to 48 percent for women.
Hemoglobin (Hgb or Hb) is the protein molecule in red blood cells that carries oxygen as blood circulates throughout the body. Hemoglobin gives blood its red color. The hemoglobin test measures the amount of hemoglobin in a patient’s blood and gives a good indication of a blood cell’s ability to transport oxygen. The normal range for hemoglobin varies slightly between the sexes, with a normal value of 13 to 18 grams per deciliter for men and 12 to 16 grams per deciliter for women.
Other items that may be included on a CBC test are:
- Mean corpuscular volume or mean cell volume (MCV). The average size of a red blood cell.
- Mean corpuscular hemoglobin (MCH). The average amount of hemoglobin per red blood cell.
- Mean corpuscular hemoglobin concentration (MCHC). The average concentration of hemoglobin per red blood cell.
White blood cell tests
A major test of the white blood cells is the white blood cell (WBC or leukocyte) count. This test counts the number of white blood cells within a specific amount (usually a cubic millimeter) of blood. White blood cells protect the body from infection by attacking invading bacteria, viruses and other foreign materials in the body. In addition, some white blood cells can attack cancer cells.
Though fewer in number than red blood cells, the number of white blood cells rises dramatically when bacterial infection is present. Therefore, a WBC is commonly used to indicate the presence of an infection such as appendicitis. WBC count helps in the diagnosis and management of a blood disease such as leukemia or to monitor the body’s response to cancer treatment. A high WBC count is one possible sign of advanced Hodgkin’s lymphoma. The normal range for this test varies slightly from lab to lab but usually falls within 4,300 and 10,800 white blood cells per cubic millimeter of blood.
In addition to counting the total number of white blood cells, a differential count may be performed to determine the different types of white blood cells present in a blood sample. There are five major types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils and basophils. Expressed as a percentage of the examined white blood cells, the normal range for the different types of white blood cells in a blood sample is as follows:
- Neutrophils (47 to 77 percent). Also known as polys, PMNS or granulocytes, neutrophils are the most common type of white blood cell in circulation. Their numbers become elevated when bacterial infection is present. A subtype of neutrophils is band neutrophils. This is an immature form of normal neutrophils that normally represents only 0 to 3 percent of the white blood cells in peripheral blood. When their number increases, it can signal an infection such as appendicitis, abscess or bacterial pneumonia.
- Lymphocytes (16 to 43 percent) are found to be elevated in some types of leukemia or viral infections, cancer and tuberculosis.
- Monocytes (0.5 to 10 percent) are found to be elevated in different kinds of leukemia.
- Eosinophils (0.3 to 7 percent) are found to be elevated in many allergic states.
- Basophils (0.3 to 2 percent) can be elevated in different types of blood disease and poisonings.
Each of these different types of white blood cells plays a different role in protecting the body. Examination and the percentage of each type of white cell present can provide important information about the patient’s immune system. The maturity of the white cells present or abnormal number of various types of white blood cells can provide valuable information about infection, allergies, reaction to drugs, radiation or the presence of blood diseases such as leukemia.
A major test of the platelets is the platelet (thrombocyte) count. This test counts the number of platelets within a specific amount (usually a cubic millimeter) of blood. Platelets are the smallest type of blood cell and play a major role in blood clotting. Too few platelets can lead to uncontrolled bleeding. Too many platelets can lead to the formation of a potentially dangerous blood clot in a blood vessel. Normal range values vary slightly between laboratories but usually fall between 150,000 and 400,000 per cubic millimeter.
Understanding test results
Normal values for complete blood counts vary from lab to lab and are not the same for all patients. Factors that must be included in a determining a normal level for a patient include the age, sex and general health of the patient. In addition, the results can be affected by the sample type and altitude levels.
Abnormal levels of one or all parts of a CBC may indicate a variety of conditions, as shown below:
- Red blood cell tests. High levels of RBC, hematocrit or hemoglobin can indicate a lack of fluid in the body or certain primary blood diseases, such as polycythemia vera. This may be caused by smoking, congenital heart disease (cardiac abnormality, defect or malformation that is present from birth), dehydration or kidney disease. Low levels are usually an indicator of anemia, which could be caused by blood loss, dietary factors or blood disorders and diseases.
Patients whose red blood cell count falls too low during cancer treatment may require a blood transfusion or treatment with a growth factor to boost the bone marrow’s red blood cell production.
- White blood cell tests. High WBC levels may indicate a heart attack, infection or an inflammatory disease such as rheumatoid arthritis. Severe emotional stress or tissue damage, such as burns, can also cause an elevated WBC. Low levels can be caused by kidney or liver disease, radiation exposure or the presence of a toxic substance in the body. The WBC differential can also help to determine the cause of high WBC levels. For instance, an elevated neutrophil level usually indicates a heart attack or infection. Lymphocyte increases can be a sign of leukemia or viral infection, while increased eosinophils can be a sign of an allergic reaction.
When a patient’s white blood cell count drops too low, cancer treatments may be postponed or adjusted in hopes of boosting the count. In addition, a physician may prescribe treatment with a growth factor to boost white blood cell production in the bone marrow.
- Platelet tests. Platelet levels may be increased by severe bleeding, infection, strenuous exercise, pregnancy, blood diseases and other factors. Low levels are usually caused by an infection or a lack of either folic acid or vitamin B-12. They also may indicate certain primary benign blood diseases and blood cancers.
Cancer patients with low platelet counts may require a platelet transfusion to help prevent bleeding or excessive bruising.
Frequency of testing
If a CBC uncovers a blood disorder or disease such as leukemia, the patient will likely be required to have frequent CBC tests. This helps a physician to monitor the effectiveness of treatments and the progression of the disease.
Patients will also require regular CBC testing while undergoing cancer treatments such as chemotherapy or radiation therapy to monitor their health. Patients with low blood cell counts may be given growth factors, which are medications that and help the bone marrow to produce blood cells or have their treatment schedule altered.
Questions for your doctor about CBC
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor or healthcare professional the following questions about complete blood cell (CBC) testing:
- What can the CBC tell you about my health?
- Should a CBC be done as a part of my annual physical examination?
- Where can I have my blood test performed?
- When and from whom can I expect the results?
- What results will indicate an abnormal condition?
- What diagnostic tests might follow a CBC?
- What types of cancer might be detected with a CBC?
- What can a CBC tell me about my cancer treatments?
- How often will I need CBC tests during treatment?
- Will I need regular blood tests after I complete my treatments?