Codocytes, also known as target cells, are

red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

s that have the appearance of a shooting target with a

bullseye Bullseye or Bull's Eye may refer to: Symbols * ◎ (Unicode U+25CE BULLSEYE), in the Geometric Shapes Unicode block * (Unicode U+0298 LATIN LETTER BILABIAL CLICK), the phonetic symbol for bilabial click Animals and plants * Bull's Eye, '' Eury ...

. In optical microscopy these cells appear to have a dark center (a central, hemoglobinized area) surrounded by a white ring (an area of relative pallor), followed by dark outer (peripheral) second ring containing a band of

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

. However, in electron microscopy they appear very thin and bell shaped (hence the name codo-: bell). Because of their thinness they are referred to as leptocytes. On routine smear morphology, some people like to make a distinction between leptocytes and codocytes- suggesting that in leptocytes the central spot is not completely detached from the peripheral ring, i.e. the pallor is in a C shape rather than a full ring. These cells are characterized by a disproportional increase in the ratio of surface

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

area to volume. This is also described as a "relative membrane excess." It is due to either increased red cell surface area (increased beyond normal), or else a decreased intracellular hemoglobin content (which may cause an abnormal decrease in cell volume without affecting the amount of membrane area). The increase in the surface area to volume ratio also gives the cell decreased osmotic fragility, as it allows it to take up more water for a given amount of osmotic stress. In vivo (within the blood vessel), the codocyte is a bell-shaped cell. It assumes a "target" configuration only when processed to obtain a blood film. In the film these cells appear thinner than normal, primarily due to their pallor (by which thickness is judged on microscopy). When the cells are flattened out on a smear, the top of the bell is pushed to the center creating a central target with a relatively high quantity of hemoglobin.

Causes

Target cells may appear in association with the following conditions: *

Liver disease Liver disease, or hepatic disease, is any of many diseases of the liver. If long-lasting it is termed chronic liver disease. Although the diseases differ in detail, liver diseases often have features in common. Liver diseases File:Ground gla ...

: Lecithin–cholesterol acyltransferase (LCAT) activity may be decreased in obstructive liver disease. Decreased enzymatic activity increases the cholesterol to phospholipid ratio, producing an absolute increase in surface area of the red blood cell membranes or may be increased red cell membrane fluidity. *

Alpha-thalassemia Alpha-thalassemia (α-thalassemia, α-thalassaemia) is an inherited blood disorder and a form of thalassemia. Thalassemias are a group of inherited blood conditions which result in the impaired production of hemoglobin, the molecule that carrie ...

and

beta-thalassemia Beta-thalassemia (β-thalassemia) is an inherited blood disorder, a form of thalassemia resulting in variable outcomes ranging from clinically asymptomatic to severe anemia individuals. It is caused by reduced or absent synthesis of the beta ...

* Hemoglobin C Disease *

Iron deficiency anemia Iron-deficiency anemia is anemia caused by a lack of iron. Anemia is defined as a decrease in the number of red blood cells or the amount of hemoglobin in the blood. When onset is slow, symptoms are often vague such as feeling tired, weak, sh ...

* Post-

splenectomy A splenectomy is the surgical procedure that partially or completely removes the spleen. The spleen is an important organ in regard to immunological function due to its ability to efficiently destroy encapsulated bacteria. Therefore, removal of ...

: A major function of the spleen is the clearance of opsonized, deformed, and damaged erythrocytes by splenic

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

s. If splenic macrophage function is abnormal or absent because of splenectomy, altered erythrocytes will not be removed from the circulation efficiently. Therefore, increased numbers of target cells may be observed. *

Autosplenectomy An autosplenectomy (from'' 'auto-' ''self,'' '-splen-' ''spleen,'' 'List of -ectomies, -ectomy' ''removal) is a negative outcome of disease and occurs when a disease damages the spleen to such an extent that it becomes shrunken and non-functional. ...

caused by

sickle cell anemia Sickle cell disease (SCD), also simply called sickle cell, is a group of inherited haemoglobin-related blood disorders. The most common type is known as sickle cell anemia. Sickle cell anemia results in an abnormality in the oxygen-carrying ...

or hyposplenism in

coeliac disease Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine. Patients develop intolerance to gluten, which is present in foods such as wheat, rye, spelt ...

In patients with obstructive liver disease, lecithin cholesterol acetyltransferase activity is depressed, which increases the cholesterol-to-phospholipid ratio and produces an absolute increase in the surface area of the red cell membrane. In contrast, membrane excess is only relative in patients with iron-deficiency anemia and thalassemia because of the reduced quantity of intracellular hemoglobin. When a cell membrane collapses it becomes static and stops pulsating. Target cell formation decreases the amount of oxygen that is circulated through the blood and delivered to all areas of the body.

Symptoms

Elevations in target cells are the result of a shift in the exchange equilibrium between the red blood cells and the cholesterol. Also, the surface membrane to volume ratio is increased. Target cells are more resistant to osmotic lysis, which is mostly seen in dogs. Hypochromic cells in iron deficiency anemias also can show a target appearance. Target cells are abnormally resistant to saline.

Etymology

From

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

, ''κώδων'': bell.

References

External links

* http://arbl.cvmbs.colostate.edu * https://web.archive.org/web/20070406081637/http://biomedx.com/microscopes/training/LB2.html * http://www.ornl.gov {{Abnormal clinical and laboratory findings Abnormal clinical and laboratory findings for RBCs