A complete blood count is also called a CBC for short. It is a screening test that is used to diagnose many different disorders of the blood, including anemia and infection. A CBC measures the following important features of the blood:

  • number of red blood cells, called RBCs for short
  • number of white blood cells, called WBCs for short
  • number of platelets
  • total amount of hemoglobin in the blood
  • percentage of blood composed of cells, called hematocrit
  • other special tests as needed

The test is fast and virtually pain free.

How is this test done?

To take a blood sample from a vein on your forearm or hand, your doctor or nurse will follow these steps.

  • Clean the skin over your vein with an antiseptic.
  • Wrap a strong rubber tube, called a tourniquet, around your upper arm. Doing this enlarges the veins in your lower arm by restricting blood flow through them. Enlarged veins are easier to take blood from.
  • Gently insert a small needle into your vein.
  • Collect a small sample of your blood in a syringe or vial.
  • Remove the tourniquet.
  • Withdraw the needle.
  • Cover the puncture site with a bandage and apply pressure to stop any bleeding.