A Patient’s Guide to Understanding the Complete Blood Count

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A Patient’s Guide to Understanding the CompleteBlood Count

There may be instances in your life when the doctor orders a complete blood count for you, either as a baseline test as part of a routine physical or as a response to symptoms you’ve been experiencing.

The goal of this blog post is to help you understand what a complete blood count is, why it is it ordered, and what possible tests may be ordered as a follow-up to the CBC blood test. Lab tests can be confusing, and this article is to help eliminate some of the confusion associated with what the results of this blood test may mean. It is always best to speak with your healthcare provider concerning your results.This article is to enhance your understanding of what those results may mean.

What is a Complete Blood Count or CBC?

A CBC or complete blood count is a baseline blood test frequently ordered by health care practitioners to determine certain aspects of health. Usually, the CBC requires no fasting or preparation for the test and consists of a simple blood draw from the phlebotomist. The CBC is a commonly ordered test that provides information about:

  • The production of blood
  • The oxygen-carrying capacity of blood
  • The clotting ability of blood
  • Information on immune-fighting abilities
  • Certain conditions and cancers 

Why is a Complete Blood Count ordered?

Your healthcare provider may order a complete blood count as part of a routine check-up or to rule out certain conditions or diseases. Based on your CBC blood test results, further follow-up tests may be ordered.

  • Diagnosis
  • Monitoring
  • Screening

Complete blood counts or CBC blood tests are laboratory tests to rule out or monitor:

  • Infections
  • Anemia
  • Diseases of the immune system
  • Certain  cancers
  • Abnormal bleeding disorders such as clotting or hemorrhages

Components of the Complete Blood Count (CBC)

Red blood cells: The red blood cells in your blood are responsible for transporting oxygen from your lungs to the tissues of the body and for removing carbon dioxide from your tissues and, ultimately, from your body. Red blood cells carry hemoglobin which are proteins that bind with oxygen to transport throughout the body. They are produced in the bone marrow and live about 120days.

  • Too many RBC’s can indicate dehydration
  • Too few RBC’s can indicate blood loss or anemia
  • Size and shape can provide clues
Examples of conditions that may cause RBC count abnormalities High

Sleep apnea, pulmonary fibrosis, kidney disease, anabolic steroid use, certain kidney cancers

Any condition that would cause anemia, hemorrhage, hidden bleeding, bone marrow disease, sickle cell anemia

White blood cells: These cells, present in your blood, are a part of your body’s immune system and fight off infections. There are five different kinds of white blood cells. When your healthcare provider orders a CBC with differential, they are assessing the quantity and quality of white blood cells. The differential illustrates the amount of each type of white blood cell circulating in the blood which can indicate certain illnesses, infections, or allergic responses.An increase or decrease in the total white blood count provides certain information, and the increase or decrease in the type of white blood cells provides even more detailed information. Assessment of WBCs through automated or manual differential provides information on autoimmune and inflammatory diseases, bacterial and viral infections, cancers such as leukemia or HodgkinDisease, and allergic reactions.

  • Neutrophils: Largest percentage of WBC’s that fight inflammatory and infectious disease and are produced in the bone marrow.
  • Lymphocytes: Lymphocytes are found primarily in the lymph system. Examples are B-cells and T-cells that fight bacteria, viruses, and other pathogens
  • Monocytes: Work with neutrophils to cleanup dead or damaged cells and fight
  • Eosinophils: Elevated in allergies and some types of infections
  • Basophils: Elevate early in infection and increase in wounds
Examples of conditions that may cause abnormal WBC counts High

Infection, lymphoma, leukemia, polycythemia vera

Leukemia, lupus, aplastic anemia, chemotherapy, AIDS, hypersplenism

Platelets: Also called thrombocytes, platelets are blood components involved in clotting.

  • Platelet counts can be high or low. When platelets are low, the patient is at risk for hemorrhage. High platelet counts place a patient at risk for clotting abnormally.
Examples of conditions that may cause abnormal platelet counts High
Acute Blood Loss


Hemoglobin: This protein is present in each red blood cell and is the binding site for oxygen molecules for their transport in the blood.

  • When hemoglobin is low, then there are less transport molecules for oxygen to bind to and this could cause low oxygen availability to the tissues.
Examples of conditions that may cause abnormal hemoglobin values High
Polycythemia vera
Kidney Tumors
Heart disease
Lung scarring diseases
such as COPD
Aplastic anemia
Iron Deficiency


Hematocrit: The measure of percentage or proportion of your blood that is made up of red blood cells.  

  • The hematocrit measures the percentage of red blood cells to blood, and another important part of blood is plasma which is the colorless fluid the colorless fluid in which blood components and fat globules are suspended. This is the liquid part of blood and serves an important function.
Examples of conditions that may cause abnormal hematocrit values High
Carbon Monoxide
Congenital Heart Disease
Bone marrow issues
Nutritional Deficiency

A complete blood count or CBC also provides additional information regarding red blood cells called RBC indices.

  • Mean corpuscular volume (MCV) measures the average size of red blood cells
  • Mean corpuscular hemoglobin (MCH) measures the average amount of hemoglobin in each cell
  • Mean corpuscular hemoglobin concentration(MCHC) specifically measures the concentration of hemoglobin within the RBCs
  • Red cell distribution and width (RDW) measures the variation is the size of your RBCs

What are Normal Values for a Complete BloodCount?

After getting your CBC blood test results, your doctor will compare the values to a reference range. Provided below are the normal ranges, in adults, for each of the five blood components mentioned above.

Red blood cell count1 Males: 4.35–5.65 trillion cells/liter (L)
Females: 3.92–5.13 trillion cells/liter (L)
Hemoglobin1 Males: 13.2–16.6 grams/deciliter (dL)
Females: 11.6–15 grams/deciliter (dL)
Hematocrit1 Males: 38.3–48.6 percent (%)
Females: 35.5–44.9 percent (%)
White blood cell count1 3.4–9.6 billion cells/liter (L)
Platelet count1 Males: 135–317 billion/liter (L)
Females: 157–371 billion/liter (L)

Depending on your test results, your doctor mayor may not order further tests for follow-up.

Understanding Possible Significance of AbnormalValues

The purpose of a complete blood count is to give your healthcare provider details about the state of your health. It is an important medical tool because it uses one sample to analyze the complete spectrum of cells found in the blood as well as some of the characteristics of those cells.

The primary uses for the CBC are diagnosis, screening, and monitoring. Because it provides information about every type of cell in the blood, the CBC can provide information related to a wide variety of medical problems.

Common Follow-Up Tests Ordered FollowingAbnormal Complete Blood Count 

If some perimeters of your complete blood count are abnormal, your doctor may order follow-up tests. Common follow-up tests include C-reactive protein (CRP) blood test, erythrocyte sedimentation rate (ESR) blood test, mean platelet volume (MPV) blood test, and so on.

CRP blood test: It measures the amount of CRP protein present in your blood, which is released from your liver as a response to inflammation.Inflammation is your body’s act of protecting your tissues from the effects of infection or injury.

Levels of CRP equal to or greater than 10milligrams/liter (L) are considered high.6 A high level is a marker of inflammation, which may be due to infections, inflammation of arteries of the heart, or certain cancers.

ESR blood test: This test evaluates your body’s inflammatory response to an infection. It is most ordered by your doctor if you have unexplained fever. However, this test is not definitive on its own and is, thus, usually interpreted in conjunction with the C-reactive protein (CRP) test report.

Mean platelet volume (MPV) blood test: This test measures the average size of platelets in your blood. Platelets are involved in the blood clotting process in your body. Hence, this test can detect bleeding disorders or certain bone marrow conditions.

It’s not recommended to self-diagnose and to stress yourself out on your blood report before it is interpreted by your doctor. Blood reports are useful tools combined with a complete history, physical examination, and imaging procedures (in some cases) to determine a definitive diagnosis. Sometimes they are not accurate due to user error or sample contamination. That’s why a thorough consultation with your health care provider is always highly recommended.

Book a consultation with your primary care doctor today.