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Blood differential
Definition:
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.) Alternative Names:
Differential; White blood cell differential count Text Continues Below
How the test is performed:
Blood will be drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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 band 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:
No special preparation is necessary for adults. For infants and young children:
The preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following:
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