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Home > Patient & Family Resources > Health Library > Complete Blood Count (CBC)
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A complete blood count (CBC) gives important information about the kinds and numbers of cells in the blood, especially red blood cells, white blood cells, and platelets. 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 anemia, infection, and many other disorders.
A CBC test usually includes:
Your doctor may order a blood smear test to be done at the same time as a CBC but it is not part of the regular CBC test. In this test, a drop of blood is spread (smeared) on a slide and stained with a special dye. The slide is looked at under a microscope. The number, size, and shape of red blood cells, white blood cells, and platelets are recorded. Blood cells with different shapes or sizes can help diagnose many blood diseases, such as leukemia, malaria, or sickle cell disease.
A complete blood count may be done to:
A complete blood count may be done as part of a regular physical examination. A blood count can give valuable information about the general state of your health.
You do not need to do anything before having this test.
Your health professional drawing blood will:
If this blood test is done on a baby, a heel stick will be done instead of a blood draw from a vein.
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
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.
Men and nonpregnant women:
5,000–10,000 WBCs per cubic millimeter (mm 3) or 5.0–10.0 x 10 9 WBCs per liter (L)
4.5–5.5 million RBCs per microliter (mcL) or 4.5–5.5 x 10 12/liter (L)
4.0–5.0 million RBCs per mcL or 4.0–5.0 x 10 12/L
3.8–6.0 million RBCs per mcL or 3.8–6.0 x 10 12/L
4.1–6.1 million RBCs per mcL or 4.1–6.1 x 10 12/L
42%–52% or 0.42–0.52 volume fraction
36%–48% or 0.36–0.48 volume fraction
29%–59% or 0.29–0.59 volume fraction
44%–64% or 0.44–0.64 volume fraction
14–17.4 grams per deciliter (g/dL) or 140–174 grams per liter (g/L)
12–16 g/dL or 120–160 g/L
9.5–20.5 g/dL or 95–205 g/L
14.5–24.5 g/dL or 145–245 g/L
In general, a normal hemoglobin level is about one-third the value of the hematocrit.
Mean corpuscular volume (MCV)—Adults:
84–96 femtoliters (fL)
Mean corpuscular hemoglobin (MCH)—Adults:
28–34 picograms (pg) per cell
Mean corpuscular hemoglobin concentration (MCHC)—Adults:
32–36 grams per deciliter (g/dL)
140,000–400,000 platelets per mm 3 or 140–400 x 10 9/L
150,000–450,000 platelets per mm 3 or 150–450 x 10 9/L
7.4–10.4 mcm 3 or 7.4–10.4 fL
Blood cells are normal in shape, size, color, and number.
Red blood cell (RBC)
White blood cell (WBC, leukocyte)
Reasons you may not be able to have the test or why the results may not be helpful include:
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Current as of:
December 9, 2019
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineAdam Husney MD - Family MedicineMartin J. Gabica MD - Family Medicine
Current as of: December 9, 2019
Author: Healthwise Staff
Medical Review:E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & Martin J. Gabica MD - Family Medicine
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