Complete Blood Count (CBC): What To Think About

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What To Think About

• The white blood count can change by as much as 2,000 WBCs per microliter (mcL) from exercise, stress, or smoking.
• Children normally have higher WBC (leukocyte) counts than adults.
• Other red blood cell tests that may be done include:
  • Erythrocyte sedimentation rate (ESR). An ESR test measures how quickly red blood cells (erythrocytes) settle in a test tube. When inflammation in the body is present (such as from an infection or cancer), red blood cells may settle more slowly than normal. An ESR may help find certain inflammatory diseases when CBC results are normal. For more information, see the medical test Sedimentation Rate.
  • Reticulocyte count. This test counts the number of immature red blood cells (reticulocytes) in a blood sample. Generally, only a few reticulocytes are present in the blood in relation to mature red blood cells. But recent bleeding or mature red blood cells being destroyed can cause a lot of new reticulocytes made. This test can help find some types of anemia and check how well treatment is working. For more information, see the medical test Reticulocyte Count.
• Hematocrit measurements can be very different depending on the method and type of machine used to do the test.

Last updated:	September 12, 2008
Author:	Caroline Rea, RN, BS, MS
Reviewed By:	Anne C. Poinier, MD - Internal Medicine, Joseph O'Donnell, MD - Hematology/Oncology
Editors:	Maria Essig, Tracy Landauer