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Alternative names Return to top
Differential; White blood cell differential countDefinition Return to top
The blood differential test measures the relative numbers of white blood cells (WBCs) in the blood. It also includes information about abnormal cell structure and the presence of immature cells. (See also CBC, peripheral smear, and eosinophil count - absolute.)How the test is performed Return to top
Blood will be 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 airtight 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.
For infants or young children:
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.
After the specimen is collected from an adult or child, a drop of blood is placed on a glass slide. A smear is made and stained to differentiate the various types of WBCs for a manual differential (the cells are counted by a technician, hematologist, or pathologist rather than a computer).
How to prepare for the test Return to top
No special preparation is necessary for adults.
For infants and young children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, 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 the test will feel Return to top
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.Why the test is performed Return to top
The differential count can be used to help detect infection, anemia, and leukemia or to follow the progress of treatment.
There are various types of WBCs (also called leukocytes) that normally appear in the blood. The differential determines the relative percentages of the different types of cells in the blood, notes any abnormal appearance of the cells, and the presence of any abnormal immature cells.
Normal Values Return to top
What abnormal results mean Return to top
Any infection or acute stress results in increased production of WBCs. This usually entails an increased numbers of cells and an increase in the percent of immature cells (mainly band cells) in the blood. High WBC counts may indicate the presence of an inflammatory and immune response, or it may result from other conditions such as leukemia.
It is important to realize that an abnormal increase in one type of leukocyte can produce an apparent decrease in the percentage of other types.
An increased percentage of neutrophils may indicate:
A decreased percentage of basophils may indicate an acute allergic reaction.
This test may be performed under many other conditions as well.
What the risks are Return to top
Special considerations Return to top
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. Update Date: 5/8/2003 Updated by: Marcia S. Brose, M.D., Ph.D., Division of Hematology/Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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Page last updated: 28 October 2004 |