Alpha thalassaemia – The majority of adult haemoglobin contains two types of protein subunits, alpha globin and beta globin. Defects in the alpha globin chain lead to alpha thalassaemia, with the general complications of thalassaemia and alpha-thalassaemia specific features. Alpha globin is encoded by two virtually identical genes (HBA1 and HBA2), which with two sets of equivalent chromosomes results in four functional copies of the alpha globin gene in human. Defects in one up to all four copies of the alpha globin gene lead to alpha thalassaemia with increasing degrees of severity. A defect in one copy results in alpha minor (also called alpha+ thalassaemia trait or alpha thalassaemia trait type 2) and symptomless carrier status, defects in two copies result in mild anaemia (alpha thalassaemia trait type 1), defects in three copies give Haemoglobin H disease with anaemia and enlarged spleen, and defects in all four copies result in prenatal or neonatal death. See also Thalassaemia, Heterozygous, and Homozygous. For further details, please see the Thalassaemia Primer featured on this portal.

Anisocytosis – Variation in the size of RBCs, measured by an increased RBC distribution width (RDW)

Beta thalassaemia – The majority of adult haemoglobin contains two types of protein subunits, alpha globin and beta globin. Defects in the beta globin chain lead to beta thalassaemia, with the general complications of thalassaemia and beta-thalassaemia specific features. Beta globin is encoded by the HBB gene, and therefore by two functional copies in the human diploid (containing a set of duplicate chromosomes) genome. Defects in both gene copies results in beta thalassaemia major (also called Cooley's anaemia) with anaemia, kidney enlargement and, if untreated, death before the age of twenty. Defects in one gene copy produce beta thalassaemia minor (also called beta thalassaemia trait) and carrier status, with mild or no symptoms. Different kinds of defects can modify the severity of the disease, and thalassaemia intermedia describes patient conditions between the typical major and carrier phenotypes. See also Thalassaemia, Heterozygous, and Homozygous. For further details, please see the Thalassaemia Primer featured on this portal.

Blasts – The earliest committed precursors of red and white blood cells, which show increased accumulation during acute leukaemia in blood and marrow

Blood cell – Any of the cellular components of the blood, which separates into blood cells and serum. There are three types of blood cells, red blood cells, which facilitate oxygen transport, white blood cells, which mediate immune and inflammatory responses, and platelets, which are essential to wound closure and blood clotting.

Blood coagulation – A complex process preventing blood loss from damaged blood vessels (haemostasis). It is intiated by the attachment of platelets to a wound site (primary haemostasis} and followed by a cascade of coagulation factors that form fibrin strands which reinforce the initial haemostatic platelet plug. Coagulation disorders can lead to increased haemorrhage (e.g. in haemophilia) or thrombosis and embolism.

Carrier – A carrier (or: asymptomatic carrier) is a person infected without showing symptoms (hence, merely carrying the pathogen) or a person bearing the abnormal gene of a recessive disorder, i.e. a disorder that does not display symptoms if at least one of the two copies normally held for each gene is intact. Carriers of infection can pass the pathogen on to others who might be susceptible and develop symptoms. Genetic carriers may pass their defective gene on to their offspring, where it might lead to disease if combined with an additional defective copy from the other parent. See also Heterozygous and Homozygous.

CBC – Complete blood count. The total number of blood cells, including the number of RBCs, their size, and the numbers of white blood cells and platelets, in a volume of blood

CD34 – An antigen (protein marker) expressed on the surface of haematopoietic stem cells, therefore indicative of cells capable of producing new blood cells

Cytopenia – Reduced titre of cells circulating in the blood. Depending on the cell population affected cytopenias are differentiated into anaemia (low RBC count), leukopenia (low count of white blood cells), neutropenia (low neutrophils) as a specific leukopenia, thrombocytopenia (low platelet count), and pancytopenia (reduction of all types of blood cells).

Delta thalassaemia – Up to three percent of adult haemoglobin contains alpha and delta haemoglobin, with the remaining typical adult haemoglobin containing alpha and beta chains. Defects in the delta gene (HBD) accordingly result in very mild forms of what is observed for homozygous and heterozygous mutations in the beta gene. Frequently for delta globin defecdts, however, the proximal beta gene is affected simultaneously, leading to the more severe phenotype of a combined beta/delta thalassaemia. See also Thalassaemia. For further details, please see the Thalassaemia Primer featured on this portal.

DIC – Disseminated intravascular coagulation. DIC can have various causes, and its hallmark is the depletion of coagulation factors and platelets, as measured by extended PT and PTT, by increased D-dimer, and by a decreased platelet count. Possible causes are metastasis, sepsis or obstetric complications.

D-dimer – Cross-linked fragments of fibrin, produced as part of the blood coagulation cascade by the breakdown of cross-linked full-length fibrin. D-dimers are instrumental in sealing wounds to stop bleeding, and are a marker of activated coagulation and fibrinolysis, e.g. as part of DIC.

Erythrocyte – see red blood cell

Ferritin – Multimeric, iron-binding protein. Though generally intracellular, ferritin is found in the blood serum, with its serum levels indicating iron levels (iron load) in the body.

Haemoglobin – Haemoglobin is a metalloprotein complex and main constituent of RBCs. In vertebrates in general, haemoglobin conveys oxygen from the lungs or gills to body tissues, where it releases oxygen and binds waste carbon dioxide for reverse transport and release upon renewed oxygen uptake. Mammalian haemoglobin contains four protein chains, a haeme molecule, and an iron atom, and its protein composition is developmentally regulated. In humans, embryonic haemoglobin is a heterotetramer of xi₂epsilon₂, alpha₂epsilon₂ or xi₂gamma₂. In the fetus the main haemoglobin species is made up of alpha₂gamma₂ (Haemoglobin F, HbF), and in adults alpha₂beta₂ (HbA), with some alpha₂delta₂ (HbA2, below 3% of adult haemoglobin) and a restriction of HbF in few, so-called F cells. Defects in the structure or expression of globin chains can lead to inherited blood disorders, such as thalassaemia and sickle cell disease.

Haemolysis – Accelerated destruction of RBCs. Common causes for haemolysis are defects in the RBCs themselves (e.g. of their enzymes or cytoskeleton), mechanical disruption (as may be brought about also be the changed shape of RBCs in e.g. sickle cell disease), and antibody-mediated immune responses (as may be encountered after mismatched blood transfusion).

Haematopoiesis – Blood formation. The division of stem and precursor cells and their differentiation into distinct types of blood cells.

Heterozygous – Humans are diploid, meaning that they posses a duplicate set of chromosomes and hence two copies (a paternal and a maternal one) of most genes. Being heterozygous (heterozygosity) for a given gene means possessing two different copies of that gene (i.e. two copies encoding a different trait). If one of the traits is dominant, it will determine the phenotype (e.g. the health status) of the individual. Therefore, for dominant traits even heterozygotes show disease symptoms. For recessive disease traits, on the other hand, the healthy gene will predominate in heterozygotes, who are then symptom-free and referred to as disease carriers. The separation between dominant and recessive traits is not clear-cut, and for many conditions heterozygous individuals will show intermediate phenotypes, i.e. a comparably mild expression of disease symptoms (see e.g. thalassaemia and sickle cell disease). See also Homozygous.

Homozygous – Humans are diploid, meaning that they posses a duplicate set of chromosomes and hence two copies (a paternal and a maternal one) of most genes. Being homozygous (homozygosity) for a given gene means possessing two identical copies of that gene. Homozygotes for certain disease traits, who therefore do not have a functional copy of the gene in question, may be severely affected by disease symptoms (see e.g. thalassaemia and sickle cell disease). See also Heterozygous.

Howell-Jolly bodies – Round, blue-staining inclusions in RBCs. Their presence is caused by incomplete removal of red-blood-cell nuclei by the spleen and hence indicates splenic dysfunction.

Hypersegmentation – Increased number of segments in the nuclei of neutrophils, characteristic of megaloblastic disorders (e.g. megaloblastic anaemia)

Hypochromia – Reduced haemoglobin in RBCs, detectable in cases of iron deficiency, microcytosis, and thalassaemia as an increased central pallor in blood smears.

Leukocyte – see White blood cell

Leukoerythroblasticity – The detectability of nucleated RBCs and white cell precursors in peripheral blood, indicating an infiltrative process (panmyelophthisis) in the bone marrow.

Macrocytosis – The presence of unusually large RBCs

MCV – Mean corpuscular volume. RBC volume, measured in femtolitres (1 fL = 10^-15 L)

MCH – Mean corpuscular haemoglobin. The haemoglobin content of RBCs, measured in picograms (1 pg = 10^-12 g)

MCHC – Mean cell haemoglobin concentration. Grams of haemoglobin per 100 mL of RBCs

Megakaryocyte – The polyploid bone-marrow precursor of platelets, that reduplicates its DNA without cell division during thrombopoiesis (platelet formation), resulting in a large, lobulated nucleus and a cell size a magnitude above that of RBCs.

Megaloblast – Abnormally large RBC, typical of pernicious anaemia (a specific type of megaloblastic anaemia associated with decreased uptake of vitamin B₁₂) or of particular vitamin deficiencies

Megaloblastic anaemia – Anaemic condition in which the bone marrow contains megaloblasts (abnormally large precursors of RBCs), and the peripheral blood contains macrocytes and ovalocytes (oval-shaped RBCs) and multisegmented neutrophil granulocytes. Megaloblastic conditions are generally brought about by abnormal maturation of the nuclei of RBCs, for instance as a result of defective DNA synthesis owing to low vitamin-B₁₂ intake, pregnancy, alcoholism, or chronic liver disease.

Microangiopathic haemolytic anaemia – Widespread loss of RBCs through destruction by factors in the small blood vessels (for instance in conditions with excessive blood coagulation) and characterised by general anaemia and the presence of schistocytes (fragmented RBCs)

Microcytosis – Condition characterised by a lowered MCV. It is found, for instance, in beta-thalassaemia minor, where the smaller size of RBCs leads to a mild anaemia with symptoms of slight fatigue and weakness.

Myelodysplasia – The condition is also called myelodysplastic syndrome (MDS) and covers a range of disorders associated with ineffective haematopoiesis, often leading to cytopenia and requirement for chronic blood transfusions. MDS is generally caused by differentiation disorders of blood-cell precursors, and is therefore associated with an amplification of undifferentiated cells in the bone marrow, predisposing affected individuals to leukaemia.

Myelophthisis – Loss of bone marrow, either by wasting or atrophy of the spinal cord, or by replacement of haemopoietic tissue by abnormal tissue, such as fibrous tissue or malignant tumours. The latter process is also referred to as panmyelophthisis.

Neutrophil – The most abundant of white blood cells, of the granulocyte type and critical to the uptake (phagocytosis) of pathogens and affected cells. In the acute phase of inflammation they can leave the blood stream to act locally, where they might accumulate to become the main cellular constituent of pus.

Pancytopenia – see Cytopenia

Panmyelophthisis – see Myelophthisis

Prothrombin time – PT; the PT indicates the efficacy of the Tissue-factor blood-coagulation pathway and is the time a blood sample takes to clot after thromboplastin (tissue factor, factor III) has been added. The physiological range is between 12 and 15 seconds.

Partial thromboplastin time – PTT; the PTT indicates the efficacy of the Contact-Activation blood-coagulation pathways, and is indicative of abnormalities in blood clotting (e.g. owing to a deficiency in coagulation factors) or the effectiveness of treatment with anti-coagulants (e..g heparin). The physiological range for PTT is between 25 and 39 seconds.

Philadelphia chromosome – The product of a translocation event (movement of a piece of DNA) between chromosomes 9 and 22 leading to an artificial fusion product that results in increased cell division and inhibition of DNA repair, and consequently to chronic myelogenous leukaemia.

Platelet – thrombocyte; anuclear, disk-shaped cell fragment mediating primary haemostasis as the primary step of blood coagulation. Platelets are derived from megakaryocytes, either by rupturing of the large cells or by the continuous release of platelets from megakaryocyte pseudopodia (cellular protrusions) into the blood.

Poikilocytosis – Increase in the proportion of abnormally shaped RBCs, for instance in anaemias associated with iron deficiency.

Polychromasia – The condition is also called polychromatophilia and indicates the presence of an increased number of reticulocytes in the peripheral blood, which posses a grey-blue colour on blood smears treated with Wright's stain.

PT – see Prothrombin time

 

RBC – see red blood cell, erythrocyte

Red Blood Cell – RBC, erythrocyte

 

Reticulocyte – Immature RBCs whose organelles have not yet been reduced and can be visualised by, for instance, Wright’s stain. In healthy individuals, reticulocytes are cells recently released from the bone marrow, representing approximately 1% of blood cells and undergoing subsequent differentiation to mature RBCs.

Rouleaux – A stacked, flat-side-to-flat-side formation of RBCs. The negative surface charge of RBCs that generally keeps them apart is cancelled out by surface-binding proteins in some disease conditions, such as inflammation or acute infection, allowing coin-like stacking of RBCs in the Rouleaux formation.

Schistocyte – RBC fragment indicative of microangiopathic disease conditions, such as disseminated intravascular coagulation and thrombotic microangiopathies (e.g. thrombotic thromobocytopenic purpura), which lead to fibrin strands that mechanically disrupt passing RBCs.

Serum – The liquid, non-cellular component of the blood, which separates into serum and blood cells.

Spherocyte – A RBC shaped like a sphere rather than the usual biconcave disk. Spheroid RBCs are removed from the blood by the spleen, are less flexible, more prone to osmotic and mechanical damage, and have a smaller surface area than biconcave RBCs. They occur as the predominant RBC type in spherocytoses, such as hereditary spherocytosis (commonly caused by RBC cytoskeletal defects) or immune-mediated haemolytic anaemias, where the activity of the spleen leads to widespread auto-haemolysis.

Sickle cell disease – Abnormal forms of haemoglobin, so-called sickle haemoglobins (HbS or Hgb S), polymerise upon deoxygenation, leading to a change in the shape of RBCs to sickle or banana shape. These altered RBCs may block smaller blood vessels, leading to ischemia and infarction, and may damage inner organs, leading for instance to stroke. Sufferers have a reduced life expectancy and are most commonly persons with ethnic origin in malaria regions, where the heterozygous form of the disease, imposing very mild sickle-cell disease symptoms whilst giving relative resistance to the malaria parasite, confers a survival advantage (the so-called heterozygote advantage).

Stem cell – Rudimentary cells in multi-cellular organisms, characterised by their continued ability to divide (self-renewal) and to differentiate (pluripotency or multipotency) into a range of specialised cell types. Cells constituting the blastocyst in initial phases of development are embryonic stem cells, while adult stem cells are retained for continued maintenance of tissues later in life. Sometimes precursor cells that can still divide but are already committed to a certain lineage (multi- or unipotency) are also referred to as stem cells. For instance, haematopoietic stem cells are multipotent precursor cells that replenish blood cells by differentiation into RBCs, white blood cell, and platelets, but that have limited capacity to differentiate into other cell types.

Thalassaemia – An inherited disorder of RBCs, resulting from absence or deficiency in one or more of the constituents of haemoglobin, the protein-iron complex in RBCs facilitating oxygen transport in our body. Depending on the defective component one can differentiate between alpha-, beta-, and delta-thalassaemia. Depending on the defect, thalassaemia symptoms vary in intensity from unnoticeable to life-threatening, and include anaemia (see cytopenia) and instability of RBCs, treatable by regular blood transfusions, chelation (binding and removal) of the resulting excess iron, and curable by bone marrow transplants from compatible donors. For further details, please see the Thalassaemia Primer featured on this portal.

Thrombocyte – see platelet

TIBC – Total iron-binding capacity; see Transferrin

Transferrin – An iron-binding protein able to carry two ferric iron ions (Fe³⁺). Transferrin loaded with iron is recognised by transferrin receptors on cell surfaces, taken up in a vesicle, and following acidification of the vesicle and release of the iron inside the cell is recycled to the extracellular space. As transferrin is the predominant iron-binding protein, the medical laboratory test of the total iron-binding capacity (TIBC) of blood, assessing the degree to which iron-binding sites can be saturated, is an indirect measure of blood transferrin. 

Thrombotic thrombocytopenic purpura – TTP or Moschcowitz disease. TTP is a rare disorder of the blood coagulation system, leading to haemolysis and organ damage through increased coagulation and mechanic disruption of RBCs. A key factor in TTP is defective breakdown of von-Willebrand factor (vWF), which cross-links platelets, blood clots, and the walls of blood vessels, and in TTP leads to occlusions and shear stress in the microvasculature. See also Schistocyte.

TTP – see thrombotic thrombocytopenic purpura

WBC – see white blood cell

White blood cell – WBC, type of blood cell found after centrifugation in the white (sometimes green) Buffy-coat interphase between the red pellet of RBCs and the translucent blood plasma. There are different types of white blood cells, fulfilling a variety of functions in inflammatory and immune-response reactions. A basic categorisation of WBCs is into granulocytes (neutrophils, basophils, and eosinophils; all containing lysosomes and surrounding small intruders) and agranulocytes (lymphocytes and monocytes). Lymphocytes are subcategorised into B cells (producing antibodies for immediate immune responses, with some serving as long-term memory cells), natural killer cells, which remove infected or cancer cells, and T cells. T cells are again subdivided into three types, helper T cells (CD4+), which coordinate immune responses and are important to anti-bacterial defence, cytotoxic T cells (CD8+), which remove virus-infected cells, and gamma-delta T cells, which are intermediates between helper and cytotoxic T cells and natural killer cells. Monocytes take up pathogens (akin to neutrophils), but also serve the long-term display of pathogen fragments to T-cells for further defence responses. Monocytes can leave blood vessels and enter other tissues, where they are referred to as macrophages and mediate local immune responses.

Wright's stain – A reagent used in histology to achieve differential staining of different cell types, e.g. in blood smears and bone marrow aspirates, and in cytogenetics to stain chromosomes. The name "Wright's stain" developed as the initial application of a relatively unstable dye solution of Eosin Y and oxidated Methylene Blue was improved by, amongst others, James Homer Wright, who included methanol as a solvent and fixative.