CBC
Overview & Description
A CBC, also called a complete blood count, is a screening test used to
diagnose and manage many diseases. A CBC measures the status of important
features of the blood, including the following:
mean corpuscular hemoglobin, which is also called MCH
mean corpuscular hemoglobin concentration, which is also called MCHC
mean corpuscular volume, also called MCV
number of platelets
number of red blood cells, also called RBCs
number of white blood cells, also called WBCs
percentage of blood composed of cells, called the hematocrit
total amount of hemoglobin in the blood
Who is a candidate for the test?
A CBC is a part of routine blood testing done with physical examinations.
It is also used to help diagnose many disorders, including problems with your
blood, heart, kidneys, and nutritional status.
How is the test performed?
A blood sample is taken from a vein on your forearm or hand. First, the skin
over your vein is cleaned with an antiseptic. Next, a strong rubber tube, called a tourniquet,
is wrapped around your upper arm. This enlarges the veins in your lower arm by restricting
blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet
is removed. Blood flows from your vein through the needle and into a syringe
or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a
short time. This helps stop or prevent bleeding at the site.
Preparation & Expectations
What is involved in preparation for the test?
Request specific instructions from your doctor.
Results and Values
What do the test results mean?
Normal values are as follows:
RBC (value changes with altitude): Male, 4.7-6.1 million cells/mcl; female,
4.2-5.4 million cells/mcl
WBC: 4,500-10,000 cells/mcl
hematocrit (varies with altitude): Male, 40.7-50.3%; female, 36.1-44.3%
hemoglobin (varies with altitude): Male, 13.8-17.2 gm/dcl; female, 12.1-15.1
gm/dcl
MCV: 80-95 femtoliter
MCH: 27-31 pg/cell
MCHC: 32-36 gm/dl
Abbreviations:
cells/mcl = cells per microliter
gm/dl = grams per deciliter
pg/cell = picograms per cell
Abnormally high numbers of red blood cells may be a sign of the following:
congenital heart disease,
which is a heart condition that you are born with
cor pulmonale,
which means a condition in which the right lower part of the heart becomes swollen
dehydration,
which is a lack of fluid in the body that can occur with conditions such as severe diarrhea
kidney disease with high levels of erythropoietin, a hormone produced
in the kidney
low oxygen tension in the blood
pulmonary fibrosis, which is a hardening of the lung tissue that can make hard for you to breathe
Abnormally low numbers of red blood cells, or anemia, may be a sign of the following:
blood loss
bone marrow failure
erythropoietin deficiency,
which occurs when the kidney does not produce enough of the hormone
hemolysis, which is the destruction of RBCs from a transfusion reaction
hemorrhage, which is a loss of blood
leukemia,
which is cancer of the blood and bone marrow
malnutrition
multiple myeloma,
a cancer of the bone marrow
overhydration, which means absorption of too much fluid in your body tissues
Abnormally low numbers of white blood cells may be a sign of the following:
bone marrow failure
collagen-vascular diseases, which are any diseases that cause the small blood vessels and tissue to swell
exposure to radiation
liver or spleen disease
the presence of substances toxic to cells
High numbers of white blood cells may point to the possible presence of the following:
emotional or physical stress
infections
inflammatory diseases
leukemia
tissue damage
High hematocrit may be a sign of the following:
burns
dehydration
diarrhea
eclampsia,
a serious condition involving high blood pressure, protein in the urine and swelling of your
face and hands during pregnancy that can lead to seizures and coma
erythrocytosis, which is an unhealthy rise in the number of red blood cells
polycythemia vera,
which is an increase in the cell mass or red blood cell levels in your blood
shock
Low hematocrit may indicate that one of these conditions is present:
anemia
blood loss
bone marrow failure
hemolysis, which is the separation of hemoglobin, the oxygen-carrying component of red
blood cells, from the red blood cells
leukemia
malnutrition
multiple myeloma
overhydration
rheumatoid arthritis,
a long-term disease in which the connective tissue is destroyed
specific nutritional deficiency
Low hemoglobin values may indicate:
anemia
blood loss
Attribution
Author:David T. Moran, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:09/30/01
Reviewer:Sandy Keefe, RN, MSN
Date Reviewed:07/27/01
