Left shift or blood shift is an increase in the number of immature leukocytes in the peripheral blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

, particularly neutrophil band cell

Band cell

A band cell is a cell undergoing granulopoiesis, derived from a metamyelocyte, and leading to a mature granulocyte.It is characterized by having a nucleus which is curved, but not lobar....

s.

Less commonly, left shift may also refer to a similar phenomenon in severe erythroanemia

Anemia

Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, when reticulocyte

Reticulocyte

Reticulocytes are immature red blood cells, typically composing about 1% of the red cells in the human body.Reticulocytes develop and mature in the red bone marrow and then circulate for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells,...

s and immature erythrocyte precursors appear in the peripheral circulation.

Definition

The standard definition of a left shift is an absolute band form count greater than 700/microL. The term itself refers to the historical practice, in paper laboratory reports, of recording band form counts on the far left side of the page.[reference needed]

Morphology

It is usually noted on microscopic

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

 examination of a blood smear. This systemic effect of inflammation is most often seen in the course of an active infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 and during other severe illnesses such as hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

 and shock. Döhle bodies

Döhle bodies

Döhle bodies are light blue-gray, oval, basophilic, leukocyte inclusions located in the peripheral cytoplasm of neutrophils. They measure 1-3 µm in diameter...

 may also be present in the neutrophil's cytoplasm in the setting of sepsis or severe inflammatory responses.

Pathogenesis

It is believed that cytokines (including IL-1

IL-1

IL-1 may refer to:* Interleukin 1, a protein* Illinois' 1st congressional district* Illinois Route 1* Building 1 of Infinite Loop , the Headquarters of Apple Inc....

 and TNF

Tumor necrosis factors

Tumor necrosis factors refers to a group of cytokines family that can cause cell death . The first two members of the family to be identified were:...

) accelerate the release of cells from the postmitotic reserve pool in the bone marrow

Bone marrow

Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

, leading to an increased number of immature cells.