PY2.1-13 | Haematology — Glossary

The percentage of blood volume occupied by packed red blood cells after centrifugation; normal values are 40-54% in males and 36-48% in females

The continuous process of blood cell production from pluripotent haematopoietic stem cells in the bone marrow, producing all formed elements of blood

A self-renewing pluripotent cell in the bone marrow that gives rise to all blood cell lineages through the common myeloid and common lymphoid progenitor pathways

A glycoprotein hormone produced by peritubular interstitial cells of the kidney in response to tissue hypoxia that stimulates erythroid progenitor proliferation and differentiation in bone marrow

An immature red blood cell that retains residual RNA (visible as a reticulum with special staining); normally 0.5-1.5% of circulating RBCs; elevated count indicates increased erythropoietic activity

A quaternary protein (4 subunits, each with a globin chain and a haem group containing Fe2+) in RBCs that binds and transports oxygen; each molecule can carry 4 O2 molecules

The sigmoid curve relating PO2 to haemoglobin oxygen saturation; the sigmoid shape reflects cooperative binding; P50 (~26.6 mmHg) is the PO2 at which Hb is 50% saturated

A glycolytic intermediate in RBCs that binds deoxy-Hb and decreases oxygen affinity (right-shifts the dissociation curve), facilitating O2 release to tissues

The decrease in haemoglobin oxygen affinity (right shift of the ODC) caused by increased CO2 and decreased pH in metabolically active tissues, promoting O2 unloading where it is most needed

The yellow pigment produced from haem degradation; unconjugated bilirubin is lipid-soluble and albumin-bound; conjugated bilirubin is water-soluble and excreted in bile

Yellow discolouration of skin, sclera, and mucous membranes due to elevated serum bilirubin (>2 mg/dL); classified as pre-hepatic, hepatic, or post-hepatic based on the cause

The plasma transport protein for iron; each molecule binds two Fe3+ ions; transferrin saturation (normally 20-45%) is the ratio of serum iron to total iron-binding capacity (TIBC)

The primary intracellular iron storage protein; serum ferritin reflects total body iron stores and is the first lab parameter to decrease in iron deficiency

A peptide hormone produced by the liver that is the master regulator of iron homeostasis; it inhibits ferroportin on enterocytes and macrophages, reducing iron absorption and release into plasma

A reduction in haemoglobin concentration below the normal range (males <13 g/dL, females <12 g/dL), resulting in decreased oxygen-carrying capacity of blood

The average volume of a single red blood cell in femtolitres (fL); normal 80-100 fL; used to classify anaemias as microcytic (<80), normocytic (80-100), or macrocytic (>100)

The most abundant WBC (60-70%), characterised by a multilobed nucleus and fine granules; the first responder to bacterial infection via phagocytosis; forms pus when dead

An agranulocyte (20-30% of WBCs) responsible for adaptive immunity; T lymphocytes mediate cellular immunity and B lymphocytes produce antibodies (humoral immunity)

A hormone produced mainly by the liver that regulates platelet production by stimulating megakaryocyte proliferation and differentiation in bone marrow

A sequential series of enzymatic reactions (intrinsic, extrinsic, and common pathways) that amplify the initial clotting signal and culminate in the conversion of fibrinogen to cross-linked fibrin

A coagulation test measuring the extrinsic and common pathways (factors VII, X, V, II, I); prolonged by warfarin, liver disease, or vitamin K deficiency; INR standardises results across laboratories

A fibrin degradation product released when cross-linked fibrin is cleaved by plasmin; elevated in DIC, DVT, pulmonary embolism, and other conditions with active clot formation and breakdown

The most important natural anticoagulant; a serine protease inhibitor that inactivates thrombin, factor Xa, and other coagulation enzymes; its action is accelerated 1000-fold by heparin

The most clinically important blood group system; determined by A and B sugar antigens on RBC surfaces and corresponding naturally occurring antibodies in plasma; ABO mismatch causes acute haemolytic transfusion reactions

The D antigen on RBCs; Rh-positive individuals carry the D antigen; Rh-negative mothers can develop anti-D antibodies against Rh-positive fetal RBCs, causing haemolytic disease of the newborn in subsequent pregnancies