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The term "blood count" is often misunderstood by non-medical people. When the term is used by medical professionals it is usually referring to what is called the Complete Blood Count (CBC). This is the calculation of all of the cellular components or formed elements of a person's blood. It includes the number and distribution of the red cells, white cells and platelets, as well as the hematocrit and hemoglobin values. The white cell count is also differentiated into the various types of white cells.

When non-medical people refer to their "blood count" they are usually referring to just their hemoglobin or hematocrit values. The hematocrit is the ratio of red blood cells to the total blood volume, and is given as a percentage of the whole blood volume. The hemoglobin is the oxygen-carrying molecule within the red blood cells. Its value is given in units of weight, namely, the number of grams of hemoglobin in a liquid measure of blood. In the US and Canada it is grams per deciliter (g/dL), but in Europe grams per liter (g/L) is the preferred scale.

• The normal hemoglobin values for a male range from 13 g/dL to 18 g/dL, with an average of 15 g/dL.
• The normal hemoglobin values for a female range from 12 g/dL to 16 g/dL, with an average of 14 g/dL.
• The normal hematocrit for a male ranges from 45% to 52%, with an average of 48%.
• The normal hematocrit for a female ranges from 37% to 48%, with an average of 42%.

In the past, a hemoglobin of 10 g/dL, or a hematocrit of 30% was considered the trigger for the transfusion of red blood cells to correct anemia prior to surgery. However, these days a more conservative approach is favored by many clinicians, and transfusion decisions are now more likely to be made after evaluating the patient's overall condition. Patients without cardiovascular disease, diabetes or other underlying problems have survived with hemoglobin values as low as 1.4 g/dL (See The Transfusion Trigger - Indications for Red Cell Therapy)