···· or ····

Health Information

CBC blood test

CBC blood test


Complete blood count

A complete blood count (CBC) test measures the following:

  • The number of red blood cells (RBC count)
  • The number of white blood cells (WBC count)
  • The total amount of hemoglobin in the blood
  • The fraction of the blood composed of red blood cells (hematocrit)

The CBC test also provides information about the following measurements:

  • Average red blood cell size (MCV)
  • Hemoglobin amount per red blood cell (MCH)
  • The amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (MCHC)

The platelet count is also usually included in the CBC.

I Would Like to Learn About:

  • How the Test is Performed

    A blood sample is needed.

  • How to Prepare for the Test

    There is no special preparation needed.

  • How the Test will Feel

    When the needle is inserted to draw blood, you may feel moderate pain. Some people feel only a prick or stinging. Afterward there may be some throbbing or slight bruising. This soon goes away.

  • Why the Test is Performed

    A complete blood count (CBC) is a commonly performed lab test. It can be used to detect or monitor many different health conditions. Your health care provider may order this test:

    • As part of a routine check-up
    • If you are having symptoms, such as fatigue, weight loss, fever or other signs of an infection, weakness, bruising, bleeding, or any signs of cancer
    • When you are receiving treatments (medicines or radiation) that may change your blood count results
    • To monitor a chronic health problem that may change your blood count results, such as chronic kidney disease
  • Normal Results

    Blood counts may vary with altitude. In general, normal results are:

    RBC count:

    • Male: 4.7 to 6.1 million cells/mcL
    • Female: 4.2 to 5.4 million cells/mcL

    WBC count:

    • 4,500 to 10,000 cells/mcL


    • Male: 40.7 to 50.3%
    • Female: 36.1 to 44.3%


    • Male: 13.8 to 17.2 gm/dL
    • Female: 12.1 to 15.1 gm/dL

    Red blood cell indices:

    • MCV: 80 to 95 femtoliter
    • MCH: 27 to 31 pg/cell
    • MCHC: 32 to 36 gm/dL

    Platelet count:

    • 150,000 to 450,000/dL

    The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

  • What Abnormal Results Mean

    High RBC, hemoglobin, or hematocrit may be due to:

    • A lack of enough water and fluids, such as from severe diarrhea, excessive sweating, or water pills used to treat high blood pressure
    • Kidney disease with high erythropoietin production
    • Low oxygen level in the blood for a long time, most often due to heart or lung disease
    • Polycythemia vera
    • Smoking

    Low RBC, hemoglobin, or hematacrit is a sign of anemia, which can result from:

    • Blood loss (either sudden, or from problems such as heavy menstrual periods over a long time)
    • Bone marrow failure (for example, from radiation, infection, or tumor)
    • Breakdown of red blood cells (hemolysis)
    • Cancer and cancer treatment
    • Certain long-term (chronic) medical conditions, such as chronic kidney disease, ulcerative colitis, or rheumatoid arthritis
    • Leukemia
    • Long-term infections such as hepatitis
    • Poor diet and nutrition, causing too little iron, folate, vitamin B12, or vitamin B6
    • Multiple myeloma

    A lower than normal white blood cell count is called leukopenia. A decreased WBC count may be due to:

    • Alcohol abuse and liver damage
    • Autoimmune diseases (such as systemic lupus erythematosus)
    • Bone marrow failure (for example, due to infection, tumor, radiation, or fibrosis)
    • Chemotherapy medicines used to treat cancer
    • Disease of the liver or spleen
    • Enlarged spleen
    • Infections caused by viruses, such as mono or AIDS
    • Medications

    A high WBC count is called leukocytosis. It can result from:

    • Certain medicines, such as corticosteroids
    • Infections
    • Diseases such as lupus,rheumatoid arthritis or allergy
    • Leukemia
    • Severe emotional or physical stress
    • Tissue damage (such as from burns or a heart attack)

    A high platelet count may be due to:

    • Bleeding
    • Diseases such as cancer
    • Iron deficiency
    • Problems with the bone marrow

    A low platelet count may be due to:

    • Anemia (various types)
    • Disorders where platelets are destroyed
    • Pregnancy
    • Enlarged spleen
    • Bone marrow failure (for example, due to infection, tumor, radiation, or fibrosis)
    • Chemotherapy medicines used to treat cancer
  • Risks

    There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

    Other risks associated with having blood drawn are slight but may include:

    • Excessive bleeding
    • Fainting or feeling light-headed
    • Hematoma (blood accumulating under the skin)
    • Infection (a slight risk any time the skin is broken)
  • Considerations

    RBCs transport hemoglobin which, in turn, carries oxygen. The amount of oxygen received by body tissues depends on the amount and function of RBCs and hemoglobin.

    WBCs are mediators of inflammation and the immune response. There are various types of WBCs that normally appear in the blood:

    • Neutrophils (polymorphonuclear leukocytes)
    • Band cells (slightly immature neutrophils)
    • T-type lymphocytes (T cells)
    • B-type lymphocytes (B cells)
    • Monocytes
    • Eosinophils
    • Basophils

Related Information

  HemoglobinHematocritDehydrationAcuteChronicAnemiaCor pulmonaleIdiopathic pulmona...Polycythemia vera...Erythropoietin tes...     AnemiaHeart failureVitamins


Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 30.


Review Date: 11/26/2014  

Reviewed By: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.


A.D.A.M. content is best viewed in IE9 or above, Firefox and Google Chrome browser.
© 2015 UCHealth University of Colorado Health