PA H1 | Hematopoiesis & Blood Specimen Basics — Glossary

Progenitor derived from the HSC that gives rise to T-lymphocytes, B-lymphocytes, and NK cells.

Progenitor derived from the HSC that gives rise to all myeloid cells: red blood cells, platelets, neutrophils, monocytes, eosinophils, and basophils.

The anticoagulant in purple-top blood collection tubes. It chelates calcium irreversibly, preventing coagulation without distorting cell morphology. The correct tube for CBC, peripheral smear, reticulocyte count, and HbA1c.

The ordered developmental stages of red cell production in the marrow: proerythroblast → basophilic erythroblast → polychromatic erythroblast → orthochromatic erythroblast → reticulocyte → mature erythrocyte. The cytoplasm changes from deep blue (RNA-rich) to pink (haemoglobin-rich) across this sequence.

A glycoprotein hormone produced by peritubular cells of the kidney that drives red cell production (erythropoiesis). EPO levels rise in response to hypoxia; its absence (as in chronic kidney disease) causes anaemia.

Blood cell production occurring outside the bone marrow (in the liver, spleen, or other sites), reactivating the fetal haematopoietic potential of these organs. Occurs when marrow is overwhelmed, infiltrated, or fibrosed — classically in beta-thalassaemia major and myelofibrosis.

A cytokine that drives neutrophil production. Used clinically to mobilise HSCs from the marrow into the bloodstream before stem cell harvesting.

The continuous process by which all blood cells are produced from a common precursor in the bone marrow. In health, the marrow generates ~2 million red cells per second.

The rare, self-renewing marrow cell at the apex of the blood cell hierarchy (~0.01% of marrow cells). Two defining properties: self-renewal (produces daughter HSCs) and multipotency (can commit to any blood cell lineage).

A pre-analytical artefact caused by leaving the tourniquet on for >1 minute during venepuncture. Fluid shifts out of the vein, falsely elevating cell counts, haematocrit, and protein concentrations.

A radiological sign on lateral skull X-ray in which the diploe (inner spongy layer) is expanded by erythroid hyperplasia, producing perpendicular trabecular striations resembling hair standing on end. Pathognomonic of beta-thalassaemia major. Also causes rodent facies (frontal bossing, maxillary overgrowth) in untransfused patients.

The appearance of immature granulocytes (band cells, metamyelocytes) in the peripheral blood where they are not normally found. Signals overwhelming bacterial infection driving emergency release of marrow reserves.

A peripheral blood smear finding consisting of nucleated red cells + immature granulocytes (myelocytes, metamyelocytes) + teardrop cells (dacrocytes). This triad mandates bone marrow biopsy to look for infiltration or fibrosis.

The point at which a progenitor cell irreversibly locks into one developmental pathway (e.g., myeloid or lymphoid), driven by specific transcription factors and cytokines from the marrow microenvironment.

A giant polyploid marrow cell (~50–100 µm) that produces platelets by shedding its cytoplasm (thrombopoiesis). One megakaryocyte generates 1,000–5,000 platelets. Driven by thrombopoietin (TPO).

Immature erythroid precursors (orthochromatic or polychromatic erythroblasts) that appear in the peripheral blood — abnormal after the neonatal period. Their presence signals severe marrow stress: haemolytic anaemia, marrow infiltration, or extramedullary haematopoiesis.

The standard sequence for filling blood collection tubes to prevent additive carry-over between tubes: Blood cultures → Blue (citrate) → Red/Gold (no additive/SST) → Green (heparin) → Purple (EDTA) → Grey (fluoride-oxalate).

The last stage of red cell maturation before the fully mature erythrocyte. It contains residual ribosomal RNA (visible as a mesh on supravital staining) but has no nucleus. Normal count is 0.5–2.5% of circulating RBCs; an elevated count signals that the marrow is working hard.

A hormone produced by the liver and kidneys that drives platelet production (megakaryopoiesis). It stimulates megakaryocytes to shed their cytoplasm as platelets.

The standard method for preparing a peripheral blood film. A small drop of EDTA blood is spread across a glass slide with a second slide angled at 30–45°, then air-dried immediately and stained with Leishman or Giemsa. A well-made smear has a head, body, and tail zone; cells are read in the body where they are evenly distributed.