Complete Blood Count (CBC)

Complete Blood Count Test Results

Receiving test results

Depending on the laboratory equipment that is used, the results from a CBC can be available in a few minutes to a few days after the blood sample arrives at the laboratory. You may receive a copy of your results by mail or through an electronic health portal. Your doctor may also call you to discuss the results or to schedule an appointment to review them together.

Interpreting test results

The results from a CBC test will include separate levels listed for each component of the test including RBC, WBC, and PLT.

For each test component, the report will also show a reference range that defines what the laboratory that performed the test considers normal. These ranges, which can vary from lab to lab, are based on the results of a large sample of healthy people and help your doctor determine typical and atypical blood levels.

It is essential to talk with your doctor about the significance of your CBC test results. Your doctor will review your levels and how they compare to the laboratory’s reference ranges. They may also look at the relationships between your different blood levels and will consider your current symptoms and health history.

The following sections describe some potential causes of high or low levels of RBCs, WBCs, or PLT, but it is important to remember that an abnormal test result is not always a sign of a medical problem. Some healthy people may have blood counts that fall outside the standard reference range.

Red blood cell measurements

RBCs carry oxygen through the body, and the RBC count shows the total number of RBCs found in your blood. Hematocrit and hemoglobin are other related measures.

Anemia is a condition marked by low levels of RBCs. There are many potential causes of abnormally low levels of RBCs, hematocrit, and/or hemoglobin, including:

• Excessive acute or chronic bleeding
• Destruction of RBCs, such as in a condition called hemolytic anemia
• Disorders that affect the bone marrow, which produces new RBCs
• Nutritional deficiencies such as low iron, folate, or vitamin B12
• Some types of cancer and cancer treatment
• Chronic illnesses involving inflammation or disrupted organ function

High levels of RBCs, hematocrit, and/or hemoglobin can also have a number of possible causes. Examples include:

• Dehydration
• Heart or lung disease that reduces oxygen levels
• Certain kinds of kidney diseases
• Cigarette smoking
• Polycythemia vera, a rare disease causing overproduction of RBCs

In many cases, the CBC will include a set of measurements known as RBC indices that include the MCV, MCH, and MCHC. These indices can help distinguish between the most likely causes of anemia.

RBC counts are influenced by many different systems of the body, and sometimes abnormal levels are related to more than one factor. Your health care provider is in the best position to explain what the RBC measurements on your CBC mean for your health.

White blood cell counts

WBCs are the main players of the immune system, and the WBC count is the sum total of five different kinds of WBCs; each plays a role in immune function.

A low level of WBCs is known as leukopenia. Some of the possible causes of leukopenia include:

• Liver damage, including from alcohol abuse
• Severe infections
• An enlarged or damaged spleen
• Autoimmune diseases
• Conditions that disrupt bone marrow function
• Certain medications, including many chemotherapies for cancer

Having too many WBCs is known as leukocytosis. Excess WBCs may be related to several potential causes:

• Infections
• Tissue death from injury, burns, or other physical trauma
• Allergies and autoimmune conditions
• Stress
• Some medications
• Leukemia and some other cancers

If you have a CBC with WBC differential, your test report will show the specific levels of each kind of WBC. These are known as neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Knowing the counts of each type of WBC can provide detailed information to help your doctor interpret the findings of your CBC.

Platelet count

PLT are responsible for clotting the blood. Abnormal PLT function can mean you bleed too easily because your blood doesn’t clot properly, or your blood is prone to excess clotting.

Thrombocytopenia, a low PLT count, puts you at risk of excessive bleeding or bruising. Possible causes of a low PLT count include:

• Blood disorders that cause PLT destruction
• Some medications, including many chemotherapies
• An enlarged spleen
• Damage to the bone marrow
• Pregnancy

Having too many PLT is called thrombocytosis, and it is associated with a higher risk of cardiovascular complications from blood clots. Abnormally high PLT counts may be caused by several conditions including:

• Iron deficiency
• Some cancers
• Bone marrow dysfunction
• Recent infection or other tissue trauma

The test may also measure the MPV (the size of your PLT). The MPV level can help your doctor understand how rapidly your body is producing new PLT.

Examples of questions that you can ask your doctor to learn more about your CBC test results include:

• What does my CBC indicate about my health?
• Were any results from the test abnormal? If so, which levels were abnormal?
• Are there any diagnoses to be made based on my CBC results?
• Will any follow-up tests be needed based on my CBC results?
• Given my CBC results, is there anything that you would suggest I do to improve my health?

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