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Blood differential test

  • Definition
    • The blood differential test measures the percentage of each type of white blood cell (WBC) that you have in your blood. It also reveals if there are any abnormal or immature cells.

  • Alternative Names
    • Differential; White blood cell differential count

  • How the Test is Performed
    • A blood sample is needed.

      A laboratory specialist takes a drop of blood from your sample and smears it onto a glass slide. The smear is stained with a special dye, which helps tell the difference between various types of white blood cells.

      Five types of white blood cells, also called leukocytes, normally appear in the blood:

      • Neutrophils
      • Lymphocytes (B cells and T cells)
      • Monocytes
      • Eosinophils
      • Basophils

      A specially designed machine or a health care provider counts the number of each type of cell. The test shows if the number of cells are in proper proportion with one another, and if there is more or less of one cell type.

  • How to Prepare for the Test
    • No special preparation is necessary.

  • How the Test will Feel
    • When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

  • Why the Test is Performed
    • This test is done to diagnose an infection, anemia, or leukemia. It may also be used to monitor one of these conditions, or to see if treatment is working.

  • Normal Results
    • The different types of white blood cells are given as a percentage:

      • Neutrophils: 40 to 60%
      • Lymphocytes: 20 to 40%
      • Monocytes: 2 to 8%
      • Eosinophils: 1 to 4%
      • Basophils: 0.5 to 1%
      • Band (young neutrophil): 0 to 3%
  • What Abnormal Results Mean
  • Risks
    • There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

      Other risks associated with having blood drawn are slight, but may include:

      • Excessive bleeding
      • Fainting or feeling lightheaded
      • Hematoma (blood accumulating under the skin)
      • Infection (a slight risk any time the skin is broken)
  • References
    • Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 30.