Differential
Key points
- The blood differential test measures the relative numbers of white blood cells (WBCs) in the blood.
- Blood will be drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand.
- The area is cleansed with antiseptic and punctured with a sharp needle or a lancet.
- 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.
Alternative names
Blood differential; White blood cell differential count
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.
How the test is performed
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
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:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.