Complete blood count

A complete blood count (CBC) is a commonly ordered group of related hematology laboratory tests. Since the tests usually are done by an automated analyzer, typically the Coulter counter, it may be called a automated blood cell count. It provides a minimum set of results, some measured and some calculated. Some laboratories routinely provide additional tests; some, such as the white blood cell count differential, may be separately ordered.

Basic components

Measured

• Leukocytes (white blood cells) per unit volume
• Erythrocyte count is the number of erythrocytes (red blood cells) per unit volume
• Hematocrit
• Hemoglobin

Initial computed

Several clinically significant parameters are derived from the measured values:

• Mean corpuscular volume
• Mean corpuscular hemoglobin
• Mean corpuscular hemoglobin concentration

Optional but common

• Platelets per unit volume
• Reticulocytes per unit volume

White blood cell differential

The basic "WBC differential" gives percentages of the main types of leukocyte, not absolute counts. Some analyzers can be programmed to give counts as well. In various conditions, the count of type by unit volume is extremely important value, and may go to a subtype level, as with CD4 lymphocytes in AIDS.

• Basophils
• Eosinophils
• Band neutrophils
• Polymorphonuclear neutrophils
• Lymphocytes
• Monocytes

These percentages are commonly written in this order, from left to right. In a normal individual, the most common forms will be in the middle and, to a lesser extent, to the right. A "left shift" is indicative of an inflammatory process.