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
sickle cell disease.
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
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
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.
5,000-10,000 WBCs per cubic millimeter (mm3) or 5.0-10.0 x
109 WBCs per liter (L)
4.5-5.5 million RBCs per
microliter (mcL) or 4.5-5.5 x
4.0-5.0 million RBCs per mcL
or 4.0-5.0 x 1012/L
3.8-6.0 million RBCs per mcL
or 3.8-6.0 x 1012/L
4.1-6.1 million RBCs per mcL
or 4.1-6.1 x 1012/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
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.
picograms (pg) per cell
32-36 grams per deciliter (g/dL)
140,000-400,000 platelets per mm3 or 140-400 x
mm 3 or 150-450 x
mcm3 or 7.4-10.4 fL
Blood cells are normal in
shape, size, color, and number.
Reasons you may not be able to
have the test or why the results may not be helpful include:
CitationsFischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Other Works ConsultedChernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise StaffPrimary Medical ReviewerE. Gregory Thompson, MD - Internal MedicineAdam Husney, MD - Family MedicineSpecialist Medical ReviewerMartin J. Gabica, MD - Family Medicine
Current as ofApril 3, 2017
Current as of:
April 3, 2017
E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Martin J. Gabica, MD - Family Medicine
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Last modified on: 8 September 2017