Anisocytosis:
Unequal size of red cells. Reflected in increased red cell distribution width (RDW).

Bands:
The stage of neutrophil maturation just before full maturation. Named after the shape of the nucleus. Increased numbers of bands appear in infections.

Blasts:
The earliest committed marrow precursor of red and white blood cells. This cell accumulates in the bone marrow and blood in acute leukemia.

CBC:
Complete blood count. The most commonly ordered laboratory test in the hospital. Includes red cell number and size, white blood cell and platelet numbers.

CD34:
This refers to an antigen expressed on the surface of hematopoietic stem cells. CD34 positive cells are capable of reconstituting hematopoiesis.

DIC:
Disseminated intravascular coagulation. This condition is just like it sounds and results in depletion of coagulation factors and platelets. DIC is not by itself a diagnosis. It is "DIC caused by ____". Precipitating factors include sepsis, obstetric complications, metastatic cancer, etc. Lab studies include prolonged PT, prolonged PTT, decreased platelets, and elevated D–dimer.

D–dimer:
When the coagulation cascade is activated, fibrin is ultimately generated. Fibrin is cross–linked to form a mesh to stop bleeding. As this cross-linked fibrin is broken down, crosslinked D fragments of fibrin are generated — the D–dimer. Thus, increased levels of D–dimer signify activation of the coagulation system and the fibrinolytic system. D–dimer levels are markedly elevated in DIC.

Ferritin:
A multimeric protein which binds and stores iron within cells. Somehow, some ferritin gets out of cells into serum and serum ferritin levels usually reflect tissue levels of stored iron.

Hemolysis:
This term refers to processes which shorten red cell life span. This may occur by mechanical disruption, antibody–mediated destruction, cytoskeletal defects, and red cell enzyme deficits.

Howell–Jolly bodies:
A round, blue staining inclusion seen in red cells. This inclusion is made of nuclear remnants which have not been removed as usual by the spleen. The presence of H–J bodies signifies a lack of splenic function.

Hypersegmentation:
A descriptive term referring to the number of segments in a neutrophil nucleus. Hypersegmentation is typically seen in megaloblastic disorders.

Hypochromia:
Decreased amount of hemoglobin in red cells. This is evidenced on blood smear by increased central pallor. Usually associated with microcytosis and can be seen in iron deficiency, and thalassemia.

Left shift:
A descriptive term referring to increased numbers of early neutrophil series cells in peripheral blood. In general, an increased number of band forms are frequently seen in infections.

Leukoerythroblastic:
The presence of nucleated red cells and early white cell precursors in peripheral blood. This picture suggests an infiltrative (myelophthisic) process in the bone marrow.

Macrocytosis:
Large red cells.

MCV:
Mean cell volume. Red cell volume is measured in femtoliters, fl, (10–15 liters).

MCH:
Mean cell hemoglobin. The quantity of hemoglobin contained in the average red cell. This is measured in picograms.

MCHC:
Mean cell hemoglobin concentration. Expressed as grams of hemoglobin per deciliter of red cells.

Megakaryocyte:
The polyploid bone marrow precursor of platelets.

Megaloblastic:
A descriptive term in which large oval-shaped red cells (macro–ovalocytes) and hypersegmented neutrophils can be found in the peripheral blood. Bone marrow shows megaloblasts — red cell precursors in which the nucleus does not mature as it is supposed to. This results from defects in DNA synthesis which in turn are usually caused by folate or vitamin B12 deficiency.

Microangiopathic:
A descriptive term describing mechanically–disrupted red cells.

Microcytosis:
Small red cells. The finding of microcytosis shortens your differential for anemia to iron deficiency, thalassemia, and the anemia of chronic disease.

Myelodysplasia:
A stem cell disorder in which orderly maturation of blood cell precursors is deranged. This is not maturation arrest as seen in leukemia but rather "sick" appearing precursors usually associated with decreased numbers of blood cells produced, and those cells are commonly functionally defective.

Pancytopenia:
Decreased numbers of all cell lines.

Philadelphia chromosome:
A 9:22 chromosome translocation which is found in chronic myelogenous leukemia. This translocation artificially splices two genes together. The expression of this spliced gene product causes chronic myelogenous leukemia.

Poikilocytosis:
Altered shape of cells. Can be any shape.

Polychromasia:
On Wright's stain of peripheral blood, newly released red cells have a blue-purplish color from staining of their "RNA". Lots of these cells on smear suggest increased red cell production. Similar significance to an increased reticulocyte count.

Reticulocyte:
When red cells are stained with methylene blue, any reticulum (endoplasmic reticulum, mitochondria, nuclei, etc.) which has not been extruded is visualized. These represent cells which are recently released from the marrow, and it is expected that as they mature that the reticulum will disappear. One hundred cells are counted, and the percent of reticulum–containing cells is the reticulocyte count. Normal count is ~1 %.

Rouleaux:
This refers to red cells stacking up like coins on peripheral blood smear. Red cells normally have a net negative charge and repel each other. In conditions in which positively charged proteins are present in excess (multiple myeloma, acute infection, inflammation, etc.), the negative charge is cancelled and red cells stack up.

Schistocyte:
A fragmented red cell. This finding suggests mechanical disruption of the red cell which may be seen in DIC, TTP, and malfunctioning heart valve.

Spherocyte:
A red cell which is shaped like a sphere rather than the usual biconcave disk. This can result from inherited cytoskeleton defects or from loss of membrane and resealing as in immune hemolytic anemia.

Sickle cell:
When sickle hemoglobin is deoxygenated, it polymerizes and forms a gel. This deforms the red cell causing it to assume the characteristic sickle shape.

Stem cell:
These are the hematopoietic precursor cells which can differentiate into various cell elements. These are the cells which can reconstitute hematopoiesis.

Transferrin:
An iron carrying protein which binds to a specific transferrin receptor leading to internalization of transferrin with iron. The iron is released from transferrin and the transferrin molecule is recycled. Transferrin is the predominant iron binding protein in blood and thus the TIBC (total iron binding capacity) essentially measures transferrin.

TTP:
Thrombotic thrombocytopenia purpura. This rare disease results from abnormal platelet-endothelial cell interactions. The platelets stick to small vessel walls leading to a microangiopathic hemolytic process. The classic diagnostic pentad includes thrombocytopenia, microangiopathic anemia, fever, CNS symptoms, and renal insufficiency.

WBC:
White blood cell count

Wright's stain:
You've heard of the Gram stain for bacteria? This is the standard stain for peripheral blood smears.