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Office of Research and Development, United States Environmental Protection Agency, Washington DC, USA
Abstract
It can be annoying and time-consuming having to search for information in multiple places, which is why this handbook includes a glossary of more than 400 frequently used hematology terms. It includes descriptions of dozens of cell types including normal, abnormal, hematopoietic, and premature blood cells. The shapes and staining characteristics of 60 poikilocytes (RBCs with abnormal morphology) are described. Because many cells and many terms have more than one name, these are cross-referenced to avoid confusion. Equations for calculating MCH, MCV, and MCHC values are included; and there is a table of coagulation factors and their roles in maintaining hemostasis. There are also descriptions for hematologic diseases such as Von Willebrand disease, thalassemia, hemophilia, and pernicious anemia.
Absolute Erythrocytosis
Excessive erythropoiesis and increased erythrocyte mass in the blood due to primary or secondary causes. See also Primary Erythrocytosis and Secondary Erythrocytosis.
Absolute Polycythemia
Excessive polycythemia and increased erythrocyte mass in the blood due to primary or secondary causes. See also Primary Polycythemia and Secondary Polycythemia.
Acanthocyte
An erythrocyte with abnormal membranes that has multiple irregularly-spaced thorny projections. They are found in healthy cows and in dogs with severe liver disease. They can be evidence of a high fat diet, disorders of lipid metabolism, and hemangiosarcoma. They should not be confused with Echinocytes (burr cells).
Achromocyte
An artifact caused by the loss of hemoglobin due to intravascular hemolysis. Also called Ghost Corpuscle or Ghost Erythrocyte.
Acuminocyte
A fusiform erythrocyte similar to the fusocyte. It is found in goats, including Angoras.
Agglutination
A clumping of erythrocytes resembling a bunch-of-grapes caused by an antibody reaction. It should not be confused with rouleaux, which resembles a stack-of-coins.
Agranulocyte
A leukocyte with a single-lobed nucleus that lacks well-defined granules in the cytoplasm.
Agranulocytosis
A deficiency of granulocytes (neutrophils, eosinophils, and basophils) from the blood and/or marrow. Also called Granulocytopenia and Schultz’s Disease.
Amphophil
A cell that may be stained with either an acid or basic dye.
Anemia
A significant decrease in the erythrocyte count, hematocrit, hemoglobin concentration, and/or quantity of oxygen carrying hemoglobin due to blood loss or impaired blood production (secondary to a disease state). Anemias are morphologically classified according to erythrocyte size (based on MCV values) and hemoglobin content (based on the MCHC values) as described in Table 2.1. See also Aplastic Anemia (Refractory Anemia), Hemolytic Anemia, Hemorrhagic Anemia, Hypochromic Anemia, Hypoplastic Anemia, Macrocytic Anemia, Megaloblastic Anemia, Microcytic Hypochromic Anemia, Myelophthisic Anemia, Non-Regenerative Anemia (Non-Responsive Anemia), Normochromic Anemia, Normocytic Hypochromic Anemia, Pernicious Anemia, Regenerative Anemia (Responsive Anemia), Splenic Anemia.
Anisocytosis
An excessive variation in RBC size.
Antibody
An immunoglobulin molecule that interacts with an antigen.
Anticoagulant
Any chemical that inhibits blood coagulation in vivo or in vitro.
Antigen
A substance (foreign proteins, toxins, bacteria) that induces a specific immune response and that is acted upon by a specific antibody and/or sensitized T-lymphocyte.
Aplastic Anemia
A form of anemia in which the marrow is neither acellular nor hypoplastic, but there is a lack of cell maturation. There is often a decrease in granulocyte and thrombocyte counts. It is unresponsive to treatment. Also called Refractory Anemia.
Azurophil
Cells or granules that readily stain with blue aniline dyes. Azurophilic granules are found in the cytoplasm of lymphocytes, monocytes, monoblasts, mature megakaryocytes, promyelocytes, and in abnormal granulopoiesis. Azurophilic granules in neutrophils are called toxic granules and are found in sheep, cattle, and horses.
Avian Leukosis
See Leukosis.
Band Cell
See Band Granulocyte.
Band Granulocyte
An immature granulocyte (neutrophil, heterophil, eosinophil, basophil) that has an unsegmented, curved nucleus. Also called Stab Granulocyte, Immature Granulocyte, and Band Cell.
Barr Body
An appendage to the neutrophil nucleus in females of some species. It is composed of extra chromatin and resembles a drumstick.
Basket Cell
A degenerated cell in which the nucleus is swollen and the chromatin is separated such that it resembles a basket.
Basocytosis
See Basophilia.
Basopenia
A decrease in the absolute or differential basophilic count.
Basophil
1. A granular leukocyte that has an irregular, pale-staining multilobed nucleus (2–3 lobes) and a small number of cytoplasmic granules whose size and staining characteristics vary between species. Basophils are involved in hypersensitivity reactions and inflammation. Basophils are morphologically similar to mast cells, and serve some of the same functions. They produce and store vasoactive substances and release these chemicals upon stimulation. Basophils are produced in the bone marrow, spend only a few hours in peripheral circulation, and then migrate into body tissues. They are found in small numbers, except in rabbits.
2. A cell or element that readily stains with basic dyes.
Basophilia
1. An increase in the absolute or differential basophilic count. Also called Basocytosis.
2. The tendency of immature erythrocytes to stain bluish either diffusely, or with stippling or granules.
3. An increase in the number of circulating basophilic erythrocytes.
Basophilic
Cells or cell structures that readily stain with basic dyes.
Basophilic Erythrocyte
An immature erythrocyte that readily stains with basic dyes.
Basophilic Stippling
The blue-staining granules of ribosomal material found in immature erythrocytes. It may be found in lead poisoning when anemia is mild.
B-Cell
See B-Lymphocyte.
Berry Cell
See Echinocyte.
Blast
An immature cell in the lineage of a cell type.
Blastogenesis
The process by which mature (small) lymphocytes revert to a blast (immature) form, divide, and differentiate as in the production of plasma cells. Blastogenesis is stimulated by an antigen to which an individual has been immunized.
Bleeding Time
The time required for bleeding to stop following a controlled skin incision.
Blister cell
A feline erythrocyte that appears to have a hole punched in its periphery; caused by oxidative injury.
Blood
A fluid tissue consisting of erythrocytes (red blood cells) that transport oxygen and carbon dioxide throughout the body; several types of leukocytes (white blood cells) that serve an immune function; thrombocytes (platelets) that are required for clotting; and plasma, the liquid portion that suspends the blood cells and carries proteins, hormones, all nutrients needed by cells, and cellular wastes for elimination.
Blood Dyscrasia
An abnormal or pathological change in the blood or hematopoietic tissues.
Blood Film
The technique of spreading a thin film of blood onto a glass slide for observation and cell counting. Also called Smear.
B-Lymphocyte
A short lived lymphocyte that originates in the bone marrow of mammals and birds that is not acted upon by the thymus. In birds, B-lymphocytes differentiate in the bursa of Fabricius, which is located near the cloaca. B-lymphocytes are involved in antibody production (humoral immunity). When mature B-lymphocytes become sensitized, they can revert to a blast (immature) form, divide, and differentiate into plasma cells. Also called B-Cell, Bursa-Derived Lymphocyte (in birds), Thymus Independent Lymphocyte, Bursa Equivalent Lymphocyte, and Bone Marrow Derived Lymphocyte (in mammals).
Bone Marrow
The soft material in the cavities of bones where blood cells are formed via hematopoiesis.
Bone Marrow Derived Lymphocyte
See B-Lymphocyte.
Buffy Coat Layer
A buff-colored to pinkish layer of leukocytes, thrombocytes, nucleated erythrocytes, and poikilocytes that settles above the erythrocyte mass following centrifugation.
Bursa-Derived Lymphocyte
See B-Lymphocyte.
Bursa Equivalent Lymphocyte
See B-Lymphocyte.
Burr Cell
See Echinocyte.
Burst Forming Unit
A cell found in small numbers in the bone marrow that is derived from the multipotent hematopoietic stem cell that gives rise to the colony forming unit. It forms large colonies known as bursts.
Cabot’s ring bodies
Mitotic spindle remnants found in erythrocytes that appear as loops and figure 8’s. They are seen in severe anemia.
Cell Mediated Immune Response
An acquired immunity controlled by T-lymphocytes as in pathogen resistance (bacteria, virus, fungi), autoimmunity, graft and tumor rejection, response to malignancies, and delayed hypersensitivity reactions.
Chemotaxis
The immunologic response that draws leukocytes to a reaction site.
Clot
See Thrombus.
Clotting Factors
See Coagulation Factors.
Clotting Time (CT)
A timed measurement of whole blood coagulation in a glass tube. This test is prone to error due to contamination with tissue fluids. It is rarely performed.
Coagulation
The process whereby leakage from a blood vessel is stopped. Coagulation requires platelets and coagulation factors.
Coagulation Factors
With the exception of calcium ion (factor IV), the coagulation factors are a group of proteins required for blood clotting. Many of the coagulation factors are listed by Roman numeral in the order in which they were discovered. Most factors must be activated. The activated form is designated by adding a lower case ‘a’ after the factor number. For example, the activated form of factor XII is XIIa. All factors are found in the plasma except for thromboplastin (factor III), which is released from injured tissue. Serum contains reduced quantities of factors I, II, V, VIII, and XIII. There are extravascular pools of factors II, VIII, IX, and X. There is no factor VI. Table 8.1 list the coagulation factors and identifies them as being part of the intrinsic, extrinsic, and/or common pathways. See also Platelet Factors.
Table 8.1
Coagulation factors
I | Fibrinogen—A glycoprotein produced in the liver that is part of the common pathway. Fibrinogen is converted by proteolytic action into soluble fibrin (factor Ia) by thrombin (factor IIa) in the presence of Ca++, and then into stable fibrin in the presence of Ca++ and factor XIIIa |
II | Prothrombin—A serine protease produced in the liver (vitamin K-dependent) that is part of the common pathway. Prothrombin is converted to thrombin (factor IIa) by Ca++ and platelet phospholipid (PF-3), and facilitated by factors Xa and Va (an accelerator). Thrombin then converts fibrinogen (factor I) to soluble fibrin (factor Ia) |
III | Thromboplastin (Tissue Factor)—A protein phospholipid that forms a complex with factor VII and Ca++ to initiate coagulation by the extrinsic pathway. Thromboplastin is not found in the blood, but rather is released from injured tissue |
IV | Calcium Ions (Ca ++ )—Calcium ions are necessary throughout the intrinsic, extrinsic, and common pathways |
V | Proaccelerin (Accelerator Globulin, AcG, Labile Factor)—Proaccelerin is produced in the liver, and serves as an accelerator in converting prothrombin (II) to thrombin (IIa). It is inactivated by EDTA. It is a part of the common pathway |
VI | There is no clotting factor VI |
VII | Proconvertin (Serum Prothrombin Conversion Accelerator, SPCA, Convertin, Stable Factor)—A serine protease that is produced in the liver (vitamin K-dependent) and is part of the extrinsic pathway |
VIII | Antihemophilic Factor (Antihemophilic Globulin Cofactor I, AHG, Hemophilia A Factor)—A factor produced in the liver that is involved in the intrinsic pathway. The sex-linked recessive deficiency trait is classical hemophilia (hemophilia A) |
IX | Christmas Factor (Plasma Thromboplastin Component, PTC, Hemophilia B Factor)—A serine protease produced in the liver (vitamin K-dependent) that is involved in the intrinsic pathway. A deficiency results in Hemophilia B |
X | Stuart Factor (Stuart-Prower Factor, autoprothrombin C, Prower Factor)—A serine protease produced in the liver (vitamin K-dependent). It is the first step in the common pathway. It can be activated to factor Xa by both the intrinsic and extrinsic pathways. It can also be activated in vitro with Russell’s viper venom and trypsin. Xa activates prothrombin (II) to become thrombin (IIa) |
XI | Plasma Thromboplastin Antecedent (PTA, Antihemophilic Factor C)—A serine protease produced in the liver that is part of the intrinsic pathway |
XII | Hageman Factor (Glass Factor)—Factor XII, a serine protease of unknown origin that is converted to factor XIIa in vivo upon exposure to collagen at the site of injury, and in vitro upon exposure to glass, kaolin, asbestos, diatomaceous earth, fatty acids, and other negatively charged surfaces in what is called the contact reaction. Factor XIIa activates factors IX and XI to IXa and XIa. It is the first stage in the intrinsic pathway, and is also involved in disseminated intravascular coagulation |
XIII | Fibrin-Stabilizing Factor (Fibrinase, Fibrinoligase)—A factor produced by megakaryocytes, the liver, and the placenta that is involved in the common pathway. It converts soluble fibrin (factor Ia) into stable fibrin in the presence of Ca++. Factor XIII is activated to XIIIa by factor IIa (thrombin) |
– | High Molecular Weight Kininogen (HMW Kininogen, KMWK, Fitzgerald Factor, Williams Factor, Flaujeac Factor)—A factor that is probably produced in the liver, and is a part of the intrinsic pathway. It is involved in contact activation of factor XII, and it enhances the activation of factor XI by factor XIIa |
– | Prekallikrein (Fletcher Factor)—A serine protease produced in the liver that is involved in the intrinsic pathway. It is involved in contact activation of factor XII. |
– | Platelet Factors—Proteins and lipoproteins found in platelets that participate in blood coagulation, designated PF-1, PF-2, PF-3, and PF-4 |
– | Vitamin K—A group of lipid soluble vitamins found in many foods and synthesized in the gut. Although these are not coagulation factors, they are co-factors that are necessary for the production of coagulation factors II (prothrombin), VII, IX, and X in the liver. Vitamin K can be administered to treat poisonings caused by anticoagulant rodenticides (e.g. warfarin) that interfere with prothrombin synthesis |
Coagulation Time
See Clotting Time.
Codocyte
A Target Cell or Mexican Hat erythrocyte; a type of leptocyte. It is a thin cell with concentrations of hemoglobin in the center and the outer edge, and a pale area in between. It is found in human and canine blood during liver disease, obstructive jaundice, postsplenectomy, hemoglobinopathies, thalassemia, and congenital and acquired anemias. It is rare in other species. It may be artifactual in hypertonic plasma.
Codocytosis
The presence of codocytes.
Colony Forming Unit (CFU)
A large cell found in the bone marrow that is derived from the burst forming unit, and is found in large numbers. It forms small colonies that give rise to rubriblasts, and is responsive to erythropoietin (EPO).
Common Lymphoid Progenitor
A cell derived from the multipotent stem cell. It is a committed cell that gives rise to B-lymphocytes, T-lymphocytes, and plasma cells. Also called Lymphoid Stem Cell.
Common Myeloid Progenitor
A cell derived from the multipotent stem cell. It is a committed cell that gives rise to erythrocytes, neutrophils, heterophils, eosinophils, basophils, macrophages, and thrombocytes. Also called Myeloid Stem Cell.
Common Pathway
Blood coagulation is promoted via the intrinsic or extrinsic pathway and is then completed via the common pathway.
Complete Blood Count (CBC)
An evaluation of anticoagulated blood that includes counts of the cellular components, erythrocyte morphology, and measurements of hematocrit, hemoglobin, plasma fibrinogen, total protein, and erythrocyte fragility.
Contact Reaction
See Coagulation Factor XII.
Crenation
The notched appearance in an erythrocyte caused by delayed drying, shrinking in a hypertonic solution, or extended standing of the sample. Crenation is an artifact, not a type of poikilocyte (abnormally shaped erythrocyte).
Cryohydrocyte
Erythrocytes that lyse when stored at 4 °C for no apparent pathologic reason.
Cyanosis
Low blood oxygen that results in the skin and mucous membranes having a bluish tinge.
Cytotoxic T-Cell
A type of T-lymphocyte with previous antigenic exposure that can recognize and destroy foreign cells.
Dacryocyte
A tear-shaped erythrocyte found in dogs and cats with myeloproliferative disorders. They are found in healthy goat kids. They may be artifactual in the feathered edge of a blood smear (all points are pointing the same way).
Descicyte
See Xerocyte.
Desiccytosis
See Xerocytosis.
Diapedesis
The passage of leukocytes from intact blood vessels into the tissue.
Differential Leukocyte Count
The proportion of each type of leukocyte counted on a Wright-stained blood smear. Usually presented in percentages and/or absolute values.
Discocyte
A normal biconcave erythrocyte. Also called Normocyte.
Disseminated IntravascularCoagulation (DIC)
A coagulation disorder in which coagulation elements are reduced due to widespread clotting in the blood vessels and massive consumption of thrombocytes and coagulation factors. It is a secondary response to snake bite, neoplasia, surgery, heartworm, pancreatitis, hemorrhagic enteritis, polycythemia, and obstetric complications.
Dohle Bodies
RNA-derived rough endoplasmic reticulum that appears as round or oval blue-staining inclusions in the cytoplasm of neutrophils. They are found in cases of burns, infections, aplastic anemia, pregnancy, and poisoning.
Drepanocyte
A sickle-shaped erythrocyte that contains polymerized hemoglobin S. It is found in humans (sickle cell disease) and in sheep, goats, and deer.
Dyscrasia
See Blood Dyscrasia.
Dyserythropoiesis
Abnormal erythrocyte production.
Eccentrocyte
An erythrocyte with condensed hemoglobin in one part of the cell due to oxidative damage to the cell membrane. It is found in dogs with hemolytic anemia caused by onion and acetylphenylhydrazine poisoning.
Echinocyte
An erythrocyte with many evenly arranged small projections. Echinocytes are classified as I, II, or III based on the extent of abnormality. Echinocyte III cells are spherical and have pronounced projections (also called Burr Cell or Berry Cell). Echinocytes are found in bleeding peptic ulcers, gastric carcinoma, uremia, and azotemia. They may be artifactual. They should not be confused with acanthocytes that have uneven projections.
Echinoelliptocyte
An oval erythrocyte with evenly spaced projections found in cats with liver disease. They are rarely seen in other species.
Echinosis
An erythrocyte with a spiny appearance.
Effector Cell
Any activated lymphocyte or plasma cell that can destroy antigen coated cells and foreign material.
Elliptocyte
An oval-shaped erythrocyte found in the Camellidae family, deer, and Angora goats, and in dogs and cats with hematopoietic malignancies and some anemias. Also called Ovalocyte.
Embolus
A thrombus that travels from one part of the body to another.
Eosinopenia
A decrease in the absolute or differential eosinophil count.
Eosinophil
A granular leukocyte that is distinguished by its bright pink cytoplasmic granules and a smooth polymorphic nucleus. Eosinophils mediate allergic and inflammatory reactions, and destroy parasites. Although their appearance varies widely with different species, all eosinophils are parasitocidal, bacteriocidal, and phagocytic. Eosinophils are produced mostly in the marrow, but also in the thymus, spleen, and cervical lymph nodes. They spend only a few hours in the peripheral circulation before entering tissues. They tend to congregate near mast cells, and are found mostly in the bone marrow and ports of entry such as the skin, gastrointestinal tract, and lung.
Eosinophilia
An increase in the absolute or differential eosinophil count.
Erythemic Myelosis
A myeloproliferative disorder involving the erythropoietic tissue that is characterized by marked anemia, anisocytosis, and rubricytes in the circulation. Erythemic myelosis is seen in cats infected with feline leukemia virus, and rarely in other species.
Erythroblast
See Nucleated Erythrocyte. Also called Erythrocytoblast.
Erythroblastosis
The presence of erythroblasts in circulating blood.
Erythroblastemia
The presence of erythroblasts in circulating blood.
Erythrocyte
A blood cell that contains hemoglobin and transports oxygen to the body. Erythrocytes are anuclear in mammals, marsupials, and monotremes, but nucleated in all other vertebrates (e.g., birds and reptiles). A mammalian erythrocyte is a mature cell (i.e. not nucleated) unless specified otherwise. Also called Red Blood Cell and Red Corpuscle.
Erythrocyte Count
Erythrocytes per unit volume of blood.
Erythrocyte Fragility
The propensity of erythrocytes to lyse when subjected to physical, osmotic, or mechanical stress.
Erythrocyte Indices
Calculated values of erythrocyte status including Mean Corpuscular Hemoglobin (MCH), Mean Corpuscular Hemoglobin Concentration (MCHC), and Mean Corpuscular Volume (MCV). They are calculated from the erythrocyte count, hematocrit, and hemoglobin concentration. The indexes are used to classify anemia and assess the status of erythropoiesis.
Erythrocyte Refractile Bodies
See Heinz Bodies.
Erythrocyte Fragmentation
The normal destruction of erythrocytes. It is also the way that abnormal erythrocytes are removed. See Keratocyte and Knizocyte.
Erythrocyte Sedimentation
A measure of the amount of erythrocyte settlingRate (ESR) over an hour in a tube of anticoagulated whole blood.
Erythrocyte Stimulating
Plasma levels of erythrocyte stimulating factorFactor (ESF) are controlled by the kidneys. ESF stimulates stem cells to increase production by as much as 4–5 fold in response to anoxia.
Erythrocytoblast
See Nucleated Erythrocyte.
Erythrocytopenia
A decrease in circulating erythrocytes.
Erythrocytosis
An increased number of circulating erythrocytes, or an increase in erythrocyte mass in the blood. Also called Polycythemia. Erythrocytosis can be further characterized as follows:
• Absolute Erythrocytosis
Excessive erythropoiesis and increased erythrocyte mass in the blood due to primary or secondary causes as described below.
• Familial Erythrocytosis
Hereditary erythrocytosis.
• Primary Erythrocytosis
An increase of the total erythrocyte cell volume due to a dramatic increase in erythrocyte production while serum EPO levels are low. It is accompanied by splenomegaly and increased production of granulocytes and thrombocytes. It is caused by a myeloproliferative disease and is seen in dogs, cats, horses, and cattle. Also called Primary Polycythemia, Polycythemia Vera, and Polycythemia Rubra Vera.
• Relative Erythrocytosis
An apparent excess of circulating erythrocytes (i.e. elevated RBCs and hematocrit) due to a decrease in plasma volume. Also called Relative Polycythemia.
• Secondary Erythrocytosis
An increase in the erythrocyte count in the circulating blood because of excessive EPO production; either due to systemic hypoxia (appropriate) or an EPO secreting tumor in the kidney (inappropriate). Unlike primary erythrocytosis, there is no increased production of granulocytes and thrombocytes. Also called Secondary Polycythemia.
Erythrogenesis
Erythrocyte production. Also called Erythropoiesis.
Erythroid
Any of the developing cells that mature into erythrocytes.
Erythroleukemia
Neoplastic proliferation of erythroblastic and myeloblastic elements with the release of atypical erythroblasts and myeloblasts.
Erythron
Any cell that can be characterized as an erythrocyte or erythrocyte precursor.
Erythropenia
A decrease in circulating erythrocytes.
Erythropoiesis
Erythrocyte production. Also called Erythrogenesis.
Erythropoietin (EPO)
A glycoprotein hormone released by adult kidneys and fetal liver that stimulates erythropoiesis. In response to hypoxia, EPO binds to receptors on BFU-E and CFU-E cells in the bone marrow. This shortens cell cycle and maturation times and allows for an increased release of erythrocytes into circulation.
Extramedullary Hematopoiesis
The production of blood cells outside of the bone marrow such as in the spleen, liver, and lymph nodes.
Extrinsic Pathway
The initiatory coagulation pathway involving coagulation factors VII and III (thromboplastin from the trauma site) that then progresses to the common pathway.
Familial Erythrocytosis
Hereditary erythrocytosis.
Familial Polycythemia
Hereditary polycythemia.
Ferritin
The iron-apoferritin complex that stores iron in the body, particularly in the liver, gastrointestinal mucosa, bone marrow, spleen, and reticuloendothelial cells.
Fibrin
The insoluble fibrous protein that is the end product of coagulation. Fibrin forms a meshwork that snares blood cells to form a clot.
Fibrinogen
A plasma protein produced by the liver that is essential for clotting. It enters extravascular spaces in response to inflammatory disease, and is thus an excellent means of assessing inflammatory disease. Also called Coagulation Factor I.
Fragility Test
A test that measures the resistance of erythrocytes to hemolysis when placed in hypotonic saline solutions ranging from 0.28 % to 0.50 %, and allowed to stand for 2 h.
Fusocyte
A spindle-shaped erythrocyte similar to the acuminocyte that is found in goats, including Angoras.
Ghost Cell
Achromocyte. An artifact caused by the loss of hemoglobin due to intravascular hemolysis. Also called Ghost Erythrocyte or Ghost Corpuscle.
Gigantocyte
An erythrocyte that is 1.5-2.0 times the normal diameter. It is larger than the Macrocyte and the Megalocyte. They are normal in goats, and are seen in other species following severe anemia.
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