Left shift or blood shift is an increase in the number of immature cell types among the

blood cell A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...

s in a sample of blood. Many (perhaps most) clinical mentions of left shift refer to the

white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...

lineage, particularly

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...

-precursor

band cell A band cell (also called band neutrophil, band form or stab cell) is a cell undergoing granulopoiesis, derived from a metamyelocyte, and leading to a mature granulocyte. It is characterized by having a curved but not lobular nucleus. The term ...

s, thus signifying

bandemia Bandemia refers to an excess or increased levels of band cells (immature white blood cells) released by the bone marrow into the blood. It thus overlaps with the concept of left shift—bandemia is a principal type of left shift and many (perhaps ...

. Less commonly, left shift may also refer to a similar phenomenon in the

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

lineage in severe

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...

, when increased

reticulocyte Reticulocytes are immature red blood cells (RBCs). In the process of erythropoiesis (red blood cell formation), reticulocytes develop and mature in the bone marrow and then circulatory system, circulate for about a day in the blood stream before ...

s and immature

erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

-precursor cells appear in the peripheral circulation.

Definition

The standard definition of a left shift is an absolute band form count greater than 7700/microL. There are competing explanations for the origin of the phrase "left shift," including the left-most button arrangement of early cell sorting machines and a 1920s publication by Josef Arneth, containing a graph in which immature neutrophils, with fewer segments, shifted the median left. In the latter view, the name reflects a curve's preponderance shifting to the

left Left may refer to: Music * ''Left'' (Hope of the States album), 2006 * ''Left'' (Monkey House album), 2016 * "Left", a song by Nickelback from the album ''Curb'', 1996 Direction * Left (direction), the relative direction opposite of right * L ...

on a graph of

hematopoietic Haematopoiesis (, from Greek , 'blood' and 'to make'; also hematopoiesis in American English; sometimes also h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. ...

cellular differentiations.

Morphology

It is usually noted on

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...

examination of a

blood smear A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the ...

. This systemic effect of inflammation is most often seen in the course of an active

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

and during other severe illnesses such as

hypoxia Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

and

shock Shock may refer to: Common uses Collective noun *Shock, a historic commercial term for a group of 60, see English numerals#Special names * Stook, or shock of grain, stacked sheaves Healthcare * Shock (circulatory), circulatory medical emergen ...

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. Not much is known about their formation, but they are thought to be remnants of th ...

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

Pathogenesis

It is believed that

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

s (including IL-1 and

TNF Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...

) accelerate the release of cells from the

postmitotic The G0 phase describes a cellular state outside of the replicative cell cycle. Classically, cells were thought to enter G0 primarily due to environmental factors, like nutrient deprivation, that limited the resources necessary for proliferation ...

reserve pool in the

bone marrow Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...

, leading to an increased number of immature cells.

References

{{reflist, 30em, refs= {{cite book , first1 = Vinay , last1 = Kumar , first2 = Abul K. , last2 = Abbas , first3 = Nelson , last3 = Fausto , first4 = Stanley Leonard , last4 = Robbins , first5 = Ramzi S. , last5 = Cotran , date = 2004-07-30 , title = Robbins & Cotran Pathologic Basis of Disease , language = en , edition = 7th , location = Philadelphia, PA , publisher =

Saunders Saunders is a surname of English and Scottish patronymic origin derived from Sander, a mediaeval form of Alexander.See also: Sander (name) People * Ab Saunders (1851–1883), American cowboy and gunman * Al Saunders (born 1947), American footb ...

, isbn = 9780721601878 , lccn = 2004046835 , oclc = 249701397 , ol = 7862642M , df = dmy-all {{cite web , url = https://medicineoutofthebox.com/2010/10/26/the-meaning-of-a-shift-to-the-left/ , title = The Meaning of a Shift to the Left , last1 = Reed , first1 = Larry , date = 2010-10-26 , website = Medicine out of the box , language = en , access-date = 2022-08-05 , url-status = live , archive-url = https://web.archive.org/web/20210724135445/https://medicineoutofthebox.com/2010/10/26/the-meaning-of-a-shift-to-the-left/ , archive-date = 2021-07-24 , df = dmy-all {{cite web , url = https://www.pathologystudent.com/left-shift/ , title = Left shift , last1 = Krafts , first1 = Kristine , date = 2009-04-04 , website = Pathology Student , language = en , access-date = 2022-08-05 , url-status = live , archive-url = https://web.archive.org/web/20211214231821/https://www.pathologystudent.com/left-shift/ , archive-date = 2021-12-14 , via = , quote = The term "left shift" almost always refers to the neutrophil series. It arose during the days when cells were counted by hand using a manual counting machine. The most mature cells (segmented neutrophils) were assigned to the right-most button, the least mature cells (myeloblasts) were assigned to the left-most button, and the other stages of cells were spread out in order in the buttons in between. In a normal blood smear, virtually all the neutrophils fell under the right-most counting button, but sometimes, it was noted that there were earlier precursors present (e.g., myelocytes, metamyelocytes, or promyelocytes). In these instances, the cells were "shifted" towards the left. , df = dmy-all Pathology Hematopathology