Evaluate Your Health with a Complete Blood Count
A complete blood count (CBC) is a panel of blood tests that is used to analyze components of a person's blood. It is commonly ordered as part of routine medical check-ups and used as a screening tool to assist in evaluating a person's overall health. It is also ordered in response to symptoms that may indicate a health issue, or to aid in the diagnosis and treatment of a wide range of health conditions. Here we'll outline the details of the CBC blood test, including what it can offer in terms of assessing your health and what you can expect when you have a complete blood count done.
What the complete blood count (CBC) examines
A complete blood count test is done by analyzing a blood sample in order to provide details about different components of the blood, including:
- Red blood cells – These are the blood cells that carry oxygen into the body and carbon dioxide out. They are primarily made up of hemoglobin, an iron-containing protein that enables the cells to carry molecules of oxygen and carbon dioxide, and is responsible for the red coloration of the cells. The CBC measures the amount of these cells in the blood and examines their physical characteristics, including their shape, size, color and hemoglobin content, among other factors.
- White blood cells – These cells are the component of the blood that fights infections. The complete blood count test measures the overall amount of white blood cells in the blood. If a CBC with differential is ordered, an additional test, called a white blood cell differential, will be performed to identify the different types of white blood cells present in the blood and measure their levels.
- Platelets – A CBC measures the amount of platelets in the blood, which are blood cell fragments that aid blood clotting by sticking together to seal injuries and stop bleeding. The complete blood count test also measures the average size of platelets.
- Hematocrit – This component of the CBC measures what percentage of total blood volume is made up of red blood cells.
Includes a complete blood count (CBC), comprehensive metabolic panel (CMP), urinalysis, hemoglobin A1c, and lipid panel
Measures red and white blood cells, hematocrit, hemoglobin and platelets
These details are examined via the following blood tests that are included in a CBC test:
- White blood cell (WBC) count
- Red blood cell (RBC) count
- Platelet count
- Mean corpuscular volume (MCV)
- Mean corpuscular hemoglobin (MCH)
- Mean corpuscular hemoglobin concentration (MCHC)
- Red cell distribution width (RDW)
- White blood cell differential, when a CBC with differential is ordered
Health problems that can be detected with a complete blood count
- Anemia – A common blood disorder that interferes with oxygen transport throughout the body. It is characterized by low levels of healthy red blood cells or hemoglobin.
- Thrombocytopenia – This is a deficiency of platelets in the blood, which can cause abnormal bleeding, excessive bruising and slow blood clotting after injury.
- Autoimmune disorders – These are conditions in which the body's immune system attacks its own organs and/or tissues. Examples of autoimmune disorders include type 1 diabetes, rheumatoid arthritis, Grave's disease, Hashimoto's thyroiditis, irritable bowel syndrome, lupus, psoriasis and multiple sclerosis, among many others. A CBC can detect changes in platelet levels and other factors than can indicate autoimmune activity.
- Bone marrow problems – Various diseases and disorders can affect the ability of bone marrow to produce healthy red blood cells, white blood cells and/or platelets. Examples include leukemia and aplastic anemia.
- Heart Disease – Abnormally high levels of red blood cells, hemoglobin or hematocrit can be an indication of some forms of heart disease, and abnormalities in platelets can indicate heightened risk of heart attack or vascular disease.
- Vitamin and mineral deficiencies – some nutritional deficiencies can affect blood composition, such as iron and B-12 deficiencies, for instance.
- Inflammation – Abnormal white blood cell levels can indicate inflammation in the body.
- Infection – Abnormal white blood cell results and/or high platelet counts on a CBC can aid in diagnosing infections.
- Cancer – Certain types of cancer can cause changes in white blood cell and platelet counts.
- Lung disease – Conditions like lung cancer and chronic obstructive pulmonary disease (COPD) can cause changes in red blood cell counts.
About complete blood count test results
Test results from your complete blood count will be compared with a reference range to determine whether they are normal or may indicate a health issue that requires further investigation. According to the Mayo Clinic, normal results for adults are as follows:
Red blood cell count
- Men – 4.32-5.72 trillion cells/L (Red blood cells per liter of blood), or 4.32-5.72 million cells/mcL (cells per microliter of blood)
- Women – 3.90-5.03 trillion cells/L, or 3.90-5.03 million cells/mcL
- Men – 13.5-17.5 grams/dL (grams of hemoglobin per deciliter of blood), or 135-175 grams/L (grams per liter of blood)
- Women – 12.0-15.5 grams/dL, or 120-155 grams/L
- Men – 38.8-50.0 percent
- Women – 34.9-44.5 percent
White blood cell count
- 3.5-10.5 billion cells/L, or 3,500 to 10,500 cells/mcL
- 150-450 billion/L, or 150,000 to 450,000/mcL
It is important to note that a complete blood count may not provide a definite diagnosis for many of the health issues it can be used to detect. Rather, it can provide indications, in the form of results that are significantly above or below the normal range, that these conditions may be present, which will then be followed up with more specific testing.
Additionally, CBC blood results that are slightly above or below the normal range may not require follow-up. Slight variations are often not a cause for concern in otherwise healthy people who have no signs or symptoms of a health problem. Whether or not to pursue follow-up testing in such cases is a judgment call that should be made with your healthcare provider, with your personal health history and risk factors in mind.