Complete Blood Count (CBC)

A complete blood count (CBC) gives important information about the kinds and numbers of cells in the blood, especially Reference red blood cells Opens New Window Reference Opens New Window, Reference white blood cells Opens New Window Reference Opens New Window, and Reference platelets Opens New Window. A CBC helps your doctor check any symptoms, such as weakness, fatigue, or bruising, you may have. A CBC also helps him or her diagnose conditions, such as Reference anemia Opens New Window, infection, and many other disorders.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Normal values for the complete blood count (CBC) tests depend on age, sex, how high above sea level you live, and the type of blood sample. Your doctor may use all the CBC values to check for a condition. For example, the red blood cell (RBC) count, hemoglobin (Hgb), and hematocrit (HCT) are the most important values needed to tell whether a person has anemia, but the red blood cell indices and the blood smear also help with the diagnosis and may show a possible cause for the anemia.

To see if the white blood cell (WBC, leukocyte) count is good and how the cells look on the smear, your doctor will look at both the number (WBC count) and the WBC differential. To see whether there are too many or too few of a certain type of cell, your doctor will look at the total count and the percentage of that particular cell. There are normal values for the total number of each type of white cell.

Pregnancy can change these blood values. Your doctor will talk with you about normal values during each trimester of your pregnancy.

In general, a normal hemoglobin level is about one-third the value of the hematocrit.

High values

Red blood cell (RBC)

• Conditions that cause high RBC values include smoking, exposure to carbon monoxide, long-term lung disease, kidney disease, some cancers, certain forms of heart disease, alcoholism, liver disease, a rare disorder of the bone marrow (Reference polycythemia vera Opens New Window), or a rare disorder of hemoglobin that binds oxygen tightly.
• Conditions that affect the body's water content can also cause high RBC values. These conditions include Reference dehydration Opens New Window, diarrhea or vomiting, excessive sweating, and the use of Reference diuretics Opens New Window. The lack of fluid in the body makes the RBC volume look high. This is sometimes called spurious polycythemia.

White blood cell (WBC, leukocyte)

• Conditions that cause high WBC values include infection, inflammation, damage to body tissues (such as a Reference heart attack Opens New Window), severe physical or emotional stress (such as a fever, injury, or surgery), kidney failure, Reference lupus Opens New Window, Reference tuberculosis (TB) Opens New Window, Reference rheumatoid arthritis Opens New Window, malnutrition, Reference leukemia Opens New Window, and diseases such as cancer.
• The use of Reference corticosteroids Opens New Window, underactive Reference adrenal glands Opens New Window Reference Opens New Window, Reference thyroid gland Opens New Window Reference Opens New Window problems, certain medicines, or removal of the Reference spleen Opens New Window Reference Opens New Window can also cause high WBC values.

Platelets

• High platelet values may be seen with bleeding, iron deficiency, some diseases like cancer, or problems with the bone marrow.

Low values

Red blood cell (RBC)

• Anemia lowers RBC values. Anemia can be caused by heavy menstrual bleeding, Reference stomach ulcers Opens New Window, Reference colon cancer Opens New Window, Reference inflammatory bowel disease Opens New Window, some tumors, Reference Addison's disease Opens New Window, Reference thalassemia Opens New Window, Reference lead poisoning Opens New Window, Reference sickle cell disease Opens New Window, or reactions to some chemicals and medicines. A low RBC value may also be seen if the spleen has been taken out.
• A lack of folic acid or vitamin B12 can also cause anemia, such as Reference pernicious anemia Opens New Window, which is a problem with absorbing vitamin B12.
• The RBC indices value and a blood smear may help find the cause of anemia.

White blood cell (WBC, leukocyte)

• Conditions that can lower WBC values include Reference chemotherapy Opens New Window and reactions to other medicines, Reference aplastic anemia Opens New Window, viral infections, Reference malaria Opens New Window, alcoholism, Reference AIDS Opens New Window, Reference lupus Opens New Window, and Reference Cushing's syndrome Opens New Window.
• A large spleen can lower the WBC count.

Platelets

• Low platelet values can occur in pregnancy or Reference idiopathic thrombocytopenic purpura (ITP) Opens New Window and other conditions that affect how platelets are made or that destroy platelets.
• A large spleen can lower the platelet count.

© 1995-2011, Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Reference Terms of Use. Reference How this information was developed to help you make better health decisions.