Alternate Names: Complete blood count
How Performed: Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How To Prepare: Adult:
There is no special preparation needed.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:
How It Feels: When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Why Performed: The CBC is a screening test, used to diagnose and manage numerous diseases. It can reflect problems with fluid volume (such as dehydration) or loss of blood. It can show abnormalities in the production, life span, and destruction of blood cells. It can reflect acute or chronic infection, allergies, and problems with clotting.
MCV, MCH, and MCHC values reflect the size and hemoglobin concentration of individual cells and are useful in the diagnosis of types of anemia.
Normal Values:
- RBC (varies with altitude):
- male: 4.7 to 6.1 million cells/mcl
- female: 4.2 to 5.4 million cells/mcl
- WBC: 4,500 to 10,000 cells/mcl
- hematocrit (varies with altitude):
- male: 40.7 to 50.3 %
- female: 36.1 to 44.3 %
- hemoglobin (varies with altitude):
- male: 13.8 to 17.2 gm/dl
- female: 12.1 to 15.1 gm/dl
- MCV: 80 to 95 femtoliter
- MCH: 27 to 31 pg/cell
- MCHC: 32 to 36 gm/dl
Note: cells/mcl = cells per microliter; gm/dl = grams per deciliter; pg/cell = picograms per cell
Abnormal Results: High numbers of RBCs may indicate:
Low numbers of RBCs may indicate:Low numbers of WBCs (leukopenia) may indicate:- bone marrow failure (for example, due to granuloma (granular tumor), tumor, or fibrosis)
- presence of cytotoxic substance
- collagen-vascular diseases (such as lupus erythematosus)
- disease of the liver or spleen
- radiation exposure
High numbers of WBCs (leukocytosis) may indicate:Low hematocrit may indicate:- anemia (various types)
- blood loss (hemorrhage)
- bone marrow failure (for example, due to radiation, toxin, fibrosis, tumor)
- hemolysis (RBC destruction) related to transfusion reaction
- leukemia
- malnutrition or specific nutritional deficiency
- multiple myeloma
- over hydration
- rheumatoid arthritis
High hematocrit may indicate:Low hemoglobin values may indicate:- anemia (various types)
- blood loss
Additional conditions under which the test may be performed:
Cost:
Special Considerations: Red blood cells transport hemoglobin which, in turn, transport oxygen. The amount of oxygen received by tissue depends on the amount and function of RBCs and hemoglobin. The MCV, MCH, and MCHC reflect the size and hemoglobin content of individual red blood cells.
The hematocrit is an expression of the proportion of whole blood that is composed of red blood cells (since the contribution by the WBCs is almost negligible). The hematocrit is a compound measure of RBC number and size.
White blood cells are mediators of inflammation and the immune response. There are various types of WBCs that normally appear in the blood: neutrophils (polymorphonuclear leukocytes; PMNs), band cells (slightly immature neutrophils), T-type lymphocytes (T cells), B-type lymphocytes (B cells), monocytes, eosinophils, and basophils.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
