complete blood count

The complete blood count (CBC), ot total blood count, is one of the most basic diagnostic tests used in clinical hematology for health status assessments. The CBC is comprised of the following.


White blood cell or leukocyte (WBC)


Red blood cell or erythrocyte count (RBC)


Hemoglobin concentration (Hb)


Hematocrit (Hct)

The hematocrit is the relative volume of blood occupied by erythrocytes (red blood cells). It is abbreviated as Hct and expressed in % (volume).


Hct differs from PCV or packed cell volume in that the latter is a measured value based on a centrifuged aliquot of whole blood, whereas the Hct is a calculated value obtained by multiplying a red blood cell count (RBC) with the mean corpuscular volume (MCV). Hct is generally regarded as more accurate than the slightly higher PCV, since plasma is trapped between cells during centrifugation.


A true baseline Hct value may be hard to measure accurately for a variety of reasons. For example, when drawing a blood sample from a subject, a stress response may cause a contraction of the spleen, resulting in a momentary increase in Hct. Hct may also vary dramatically with physical activity. Average Hct values for humans range from 40 to 48%. Diving animals, and pinnipeds in particular have elevated hematocrits, with some phocid species ranging above 60%.


Mean corpuscular volume (MCV)

The mean corpuscular volume is the typical volume of one erythrocyte. It is expressed in femtoliters (fl). Normal human values of MCV range from 80 to 100 fl. Abnormal values are referred to as micro- or macro-cythaemia. MCV can be calculated as Hct/RBC (i.e. the ratio of hematocrit to red blood cell count).


Mean corpuscular hemoglobin (MCH)

The mean corpuscular hemoglobin is the amount of hemoglobin in a single erythrocyte (red blood cell). It is expressed in picograms (pg). Normal human values range from 27 to 31 pg/cell. MCH can be calculated as [Hb]/RBC (i.e. the ratio of hemoglobin concentration to red blood cell count).


Mean corpuscular hemoglobin concentration (MCHC)

The mean corpuscular hemoglobin concentration (MCHC) is the average hemoglobin concentration in erythrocytes. It is expressed in g/dl. Normal human values range from 32 to 36 g/dl. MCHC can be calculated as ([Hb]/Hct) × 100 (i.e. the ratio of hemoglobin concentration to hematocrit times 100).


Red cell distribution width(RDW)

RDW is the range of red cell sizes in one blood sample.


Platelet count (PLT)


Mean platelet volume (MPV)


The CBC with differential includes a separate listing of the five types of leukocytes.