Ontogenesis of Haemopoiesis

• Yolk sac — wk 3–8, primitive nucleated RBCs (embryonic Hb: Hb Gower)
• Liver — wk 6 to birth; main fetal site; also spleen wk 12–30
• Bone marrow — from wk 20, exclusive postnatally
• Extramedullary haemopoiesis in adults = pathological (myelofibrosis, CML, severe haemolysis)

Haemopoietic Hierarchy

• HSC → CMP (→ RBC, Plt, Granulocytes, Monocytes) + CLP (→ B, T, NK)
• HSC markers: CD34+, CD38−, Lin− (lineage negative)
• Thrombopoietin (TPO) → megakaryocytes; EPO → erythropoiesis; G-CSF → neutrophils

Reticulocyte Count

Normal Hct = 45% (M) / 40% (F). Maturation time: Hct 45%→1d, 35%→1.5d, 25%→2d, 15%→2.5d

Essential Normal Values

Blood Film — Key Findings

• Hypersegmented neutrophils (≥5 lobes) → B12/folate deficiency
• Schistocytes (helmet cells) → MAHA (TTP, HUS, DIC)
• Spherocytes → hereditary spherocytosis, AIHA
• Target cells → thalassemia, liver disease, post-splenectomy
• Sickle cells → HbSS disease
• Bite cells → G6PD deficiency (Heinz body removal by spleen)
• Pencil cells → IDA
• Acanthocytes → liver disease, abetalipoproteinaemia
• Rouleaux → myeloma, high fibrinogen
• Teardrop cells (dacrocytes) → myelofibrosis

B12 & Folate Deficiency

B12 Deficiency

• Causes: Pernicious anaemia (anti-IF antibodies, autoimmune), gastrectomy, terminal ileum disease (Crohn's), strict veganism, Diphyllobothrium latum (fish tapeworm)
• Neurology: Subacute combined degeneration — posterior columns (vibration/proprioception loss) + lateral corticospinal tracts (UMN signs)
• Schilling test (historical): distinguishes malabsorption from deficiency
• B12 stored in liver for 3–5 years → takes time to deplete

Folate Deficiency

• Causes: Poor diet, alcohol, pregnancy (increased demand), phenytoin/methotrexate (dihydrofolate reductase inhibitors), coeliac disease
• No neurological manifestations
• Stores last only 3–4 months

Megaloblastic Bone Marrow

Nuclear:cytoplasmic dissociation — nucleus lags behind cytoplasm maturation. Giant metamyelocytes, hypersegmented neutrophils (≥5 lobes in ≥5% neutrophils OR one cell with ≥6 lobes).

Iron Deficiency Anaemia

Haemochromatosis

HFE gene mutation (C282Y), AR. "Bronze diabetes" — hepatic cirrhosis, diabetes, skin pigmentation, cardiomyopathy, hypogonadism, arthropathy. Tx: phlebotomy weekly until ferritin <50 ng/mL.

Sideroblastic Anaemia

Ring sideroblasts (iron-laden mitochondria around nucleus) on Prussian blue stain. Causes: myelodysplasia (most common), alcohol, isoniazid (B6 antagonist), lead poisoning, hereditary (ALAS2 mutation, X-linked).

Hereditary Spherocytosis

• AD (most common), ankyrin/spectrin/band 3 defect → RBC loses biconcave shape → spheres trapped in spleen
• Smear: spherocytes (no central pallor, small)
• Lab: ↑ MCHC, ↑ osmotic fragility, negative DAT (distinguishes from AIHA)
• Aplastic crisis = Parvovirus B19 (attacks erythroid precursors)
• Tx: folate supplementation, splenectomy (after age 5, post-vaccine); splenectomy does NOT cure the defect but removes site of haemolysis

G6PD Deficiency

• X-linked recessive; prevalent in Africa, Mediterranean, Middle East
• G6PD → NADPH → GSH protects from oxidative stress. Absent → Hb oxidized → Heinz bodies → bite cells on smear
• G6PD level LOW during crisis (destroyed cells gone) → test 3 months later
• Favism = severe G6PD triggered by fava beans

Haemoglobinopathies

Sickle Cell Disease (HbSS)

• Vaso-occlusive crisis triggers: hypoxia, dehydration, cold, acidosis, infection
• Dactylitis (hand-foot syndrome) = first presentation in infants
• Autosplenectomy by age 5 → Howell-Jolly bodies on smear → encapsulated organisms risk (SHiN: Strep pneumo, H. flu, Neisseria)
• Acute chest syndrome = most common cause of death in adults
• Stroke — most common serious complication in children
• Priapism (sickling in corpora cavernosa)
• Osteonecrosis (AVN femoral head), osteomyelitis (Salmonella most common)
• Tx: hydroxyurea (↑ HbF), exchange transfusion (acute chest, stroke), prophylactic penicillin, vaccinations

Thalassemias

Paroxysmal Nocturnal Haemoglobinuria (PNH)

• Classic: young adult, morning haemoglobinuria (reddish urine)
• Budd-Chiari syndrome (hepatic vein thrombosis) = classic thrombotic complication
• Also: mesenteric vein thrombosis, cerebral sinus thrombosis
• Diagnosis: Flow cytometry — CD55/CD59 negative RBCs (gold standard). Ham test (historical)
• Tx: Eculizumab (anti-C5 mAb) — give meningococcal vaccine ≥2 weeks before. HSCT = curative.
• REMEMBER: PNH → Aplastic Anaemia → AML — these can transform into each other

Autoimmune Haemolytic Anaemia (AIHA)

Aplastic Anaemia

Causes

• Idiopathic (most common)
• Chloramphenicol: 2 mechanisms — (1) dose-dependent reversible; (2) idiosyncratic aplastic anaemia (~1:20,000, unpredictable, not dose-related)
• Other drugs: carbamazepine, sulfonamides, gold, NSAIDs, chemotherapy
• Viruses: hepatitis (non-A, non-B, non-C hepatitis → aplasia), EBV, CMV, parvovirus B19
• Radiation, benzene
• Inherited: Fanconi anaemia (FA; short stature, radial aplasia, café-au-lait spots, increased chromosomal breakage)
• Dyskeratosis congenita, Diamond-Blackfan (pure red cell aplasia)

Diagnosis

Pancytopenia + hypocellular BM biopsy (<25% cellularity). Exclude PNH (flow cytometry), MDS (cytogenetics).

Severity (Camitta criteria)

• Severe: ≥2 of: ANC <0.5×10⁹/L, Platelets <20×10⁹/L, Reticulocytes <1%
• Very severe: ANC <0.2×10⁹/L

Neutropenia / Agranulocytosis

• Neutropenia: ANC <1.8×10⁹/L; Severe: <0.5; Agranulocytosis: <0.1 (or <0.5 with clinical symptoms)
• Drug causes: clozapine, carbimazole (propylthiouracil), metamizole, chloramphenicol, sulfasalazine, chemotherapy
• Clozapine: MANDATORY weekly WBC monitoring for first 18 weeks
• Fever + neutropenia = neutropenic fever → empiric broad-spectrum antibiotics immediately (piperacillin-tazobactam or cefepime), no need to wait for culture
• Cyclic neutropenia: ANC drops every 21 days due to ELANE mutation

Acute Myeloid Leukaemia (AML)

• Diagnosis: ≥20% blasts in BM or PB (WHO 2016)
• Most common acute leukaemia in adults
• Key cytogenetics: t(8;21) AML-ETO (good); inv(16) CBFβ-MYH11 (good); t(15;17) PML-RARα = APL (treat with ATRA)
• Poor prognosis: complex karyotype, −5/del(5q), −7, FLT3-ITD, TP53

Auer rods = pathognomonic of AML (especially M3/APL). Myeloperoxidase positive.

Myelodysplastic Syndrome (MDS)

• Clonal disorder of HSC → dysplasia in ≥1 lineage + cytopenias; BM hypercellular despite peripheral cytopenia ("ineffective haemopoiesis")
• Ring sideroblasts (MDS-RS subtype) — SFRS2 or SF3B1 mutations
• Risk of AML transformation (especially high-grade MDS)
• del(5q) syndrome: elderly women, macrocytic anaemia, normal/↑ platelets, hypolobated megakaryocytes → lenalidomide
• IPSS-R score → prognosis; low-risk: EPO/G-CSF, lenalidomide; high-risk: azacitidine (hypomethylating agent) or HSCT

Acute Lymphoid Leukaemia (ALL)

• Most common cancer in children (peak 2–5y); B-ALL most common
• Lymphoblasts: TdT+, CD10+, CD19+ (B-ALL) or CD3+, CD7+ (T-ALL)
• t(9;22) = Philadelphia chromosome (BCR-ABL1) → worst prognosis in ALL → add imatinib/dasatinib
• CNS prophylaxis: intrathecal methotrexate (replace cranial irradiation)
• Testicular relapse in boys: sanctuary site
• T-ALL: mediastinal mass (anterior), male adolescent

Chronic Myeloid Leukaemia (CML)

• t(9;22) BCR-ABL1 (Ph chromosome) — constitutively active tyrosine kinase
• Smear: ALL stages of myeloid maturation, basophilia (↑ basophils = characteristic)
• BM: hypercellular, ↓ megakaryocytes initially
• LAP (leukocyte alkaline phosphatase): LOW in CML vs HIGH in leukemoid reaction
• Splenomegaly often massive; LDH ↑; uric acid ↑
• Tx: Imatinib (1st-gen TKI) → dasatinib/nilotinib (2nd-gen). BCR-ABL T315I mutation → ponatinib. HSCT reserved for blast crisis or failure.

Chronic Lymphocytic Leukaemia (CLL)

• Most common adult leukaemia in Western countries
• Mature B cells: CD5+ CD19+ CD23+ (CD5 is normally a T-cell marker — aberrant expression in CLL)
• Smear: Smudge cells (basket cells) = pathognomonic
• Hypogammaglobulinaemia → recurrent bacterial infections
• Autoimmune complications: AIHA (warm), ITP
• Richter transformation: CLL → aggressive DLBCL (fever, rapid lymph node growth, ↑ LDH)
• Rai staging (0–IV); Tx: watch-and-wait early; FCR (fludarabine-cyclophosphamide-rituximab) or ibrutinib (BTK inhibitor) / venetoclax (BCL-2 inhibitor)
• del(17p) / TP53 mutation → ibrutinib preferred (FCR ineffective)

Polycythaemia Vera (PV)

• JAK2 V617F mutation in 98% of cases (exon 14); JAK2 exon 12 mutation in remaining PV
• Labs: ↑ Hgb/Hct, ↑ RBC mass, ↓ EPO (key: primary erythrocytosis — distinguishes from secondary where EPO is ↑)
• Also: ↑ WBC, ↑ platelets, ↑ uric acid, splenomegaly, plethora, ruddy facies
• Risks: thrombosis (stroke, MI, Budd-Chiari), transformation to MF or AML
• Tx low-risk: phlebotomy (target Hct ≤45%) + aspirin 81mg. High-risk (age >60 or prior thrombosis): add hydroxyurea.
• Ruxolitinib (JAK1/2 inhibitor) for hydroxyurea-refractory.

Essential Thrombocythaemia (ET)

• Driver mutations: JAK2 (50–60%), CALR (26%), MPL (4%), triple-negative (10%)
• Platelets typically >450×10⁹/L, often >1,000×10⁹/L
• Paradoxical bleeding when Plt >1,000,000: acquired von Willebrand disease (large vWF multimers consumed by excess platelets)
• Caution: avoid aspirin if Plt >1M + acquired VWD (ristocetin cofactor activity <20%)
• Tx: low-risk → aspirin; high-risk → hydroxyurea + aspirin; young high-risk → anagrelide or interferon-α

Myelofibrosis (MF)

• Progressive fibrosis of BM → extramedullary haemopoiesis → massive splenomegaly
• Smear: teardrop cells (dacrocytes) + leukoerythroblastic picture (nucleated RBCs + immature WBCs)
• BM biopsy: "dry tap" (fibrosis prevents aspiration)
• Mutations: JAK2 (50%), CALR (25%), MPL (8%)
• Tx: ruxolitinib (reduces spleen size, symptoms); HSCT = only cure; luspatercept for anaemia

Bone Marrow Transplantation (HSCT)

GVHD

• Acute (<100d): skin (maculopapular rash), GI (diarrhoea), liver (cholestasis). Tx: steroids (1st line).
• Chronic (>100d): resembles autoimmune/Sjögren — dry eyes, skin fibrosis, lichenoid changes. Tx: steroids ± calcineurin inhibitors.

Engraftment Syndrome vs GVHD vs Cytokine Release Syndrome

Engraftment syndrome: fever + rash ~day 7–10 post-autologous HSCT, as neutrophils engraft. Treat with steroids. CRS: after CAR-T therapy; ↑ IL-6 → tocilizumab (anti-IL-6R).

Hodgkin Lymphoma (HL)

• Bimodal age: 20s and 65+. More common in males (except NS subtype).
• Ann Arbor staging: I (1 nodal region) → II (both sides same diaphragm) → III (both sides) → IV (extranodal)
• B symptoms: fever >38°C, drenching night sweats, weight loss >10% in 6 months
• Subtypes: Nodular Sclerosis (most common, women, mediastinal mass, lacunar RS cells) → Mixed Cellularity → Lymphocyte-rich → Lymphocyte-depleted (worst prognosis, HIV)
• NLPHL: "popcorn cells" (LP cells), CD20+, CD15−, CD30−; better prognosis
• EBV association: mixed cellularity > NLPHL
• Tx: ABVD ± radiotherapy (early); BEACOPP (advanced/relapsed)

Non-Hodgkin Lymphomas (NHL)

Aggressive Lymphomas

• DLBCL (Diffuse Large B-Cell): most common NHL. CD20+. ABC vs GCB subtypes. Tx: R-CHOP. Double-hit (MYC + BCL2 or BCL6): R-EPOCH.
• Burkitt Lymphoma: t(8;14) c-MYC/IgH. "Starry sky" pattern (high proliferation + macrophage phagocytosis). Jaw mass (endemic/Africa) or ileocaecal mass (sporadic). Highest Ki-67 (~100%). EBV-associated (endemic). Treatment: intensive chemo. Tumour lysis syndrome risk → allopurinol/rasburicase.
• Mantle Cell Lymphoma: t(11;14) cyclin D1/IgH. CD5+ CD23−. "Blastoid" variant = very aggressive. BTK inhibitor (ibrutinib) + R-CHOP.
• T-cell lymphomas: ALCL (CD30+, ALK+/−), PTCL-NOS, NK/T-cell (EBV, nasal). BV-CHP (brentuximab + CHP) for CD30+ T-cell.

Indolent Lymphomas

• Follicular Lymphoma: t(14;18) BCL2/IgH. BCL2 prevents apoptosis → "immortal" follicles. Grade 1–3a (indolent); 3b (treat as DLBCL). Waxing/waning lymphadenopathy. Tx: watch-and-wait or R-CHOP; obinutuzumab; transformation to DLBCL in 2–3%/year.
• MALT Lymphoma: Marginal zone; stomach MALT → H. pylori driven → eradicate H. pylori first (may cure). t(11;18) = H. pylori-independent (need chemoimmunotherapy).
• Hairy Cell Leukaemia: B-cell; hairy projections; BRAF V600E mutation; TRAP stain positive; massive splenomegaly, pancytopenia; "dry tap" BM. Tx: cladribine (single course = durable remission). Vemurafenib (BRAF inhibitor) for refractory.

Multiple Myeloma

• Clonal plasma cells >10% in BM producing M-protein (paraprotein)
• Lytic bone lesions (not blastic) → "punched-out" on skull XR; pathological fractures; hypercalcaemia
• AL amyloidosis: light chains deposit as amyloid → macroglossia, nephrotic syndrome, cardiomyopathy, carpal tunnel
• Rouleaux formation on smear; ESR markedly elevated
• Bence-Jones protein (free light chains in urine)
• Cytogenetics: t(4;14), t(14;16), del(17p) = high risk; hyperdiploidy = standard risk
• Tx: VRd (bortezomib-lenalidomide-dexamethasone) induction → ASCT (if eligible) → maintenance lenalidomide
• Bisphosphonates (zoledronic acid) for bone disease

Waldenström's Macroglobulinaemia

• Lymphoplasmacytic lymphoma; IgM paraprotein (large pentamer)
• MYD88 L265P mutation in 90%
• Hyperviscosity syndrome: headache, blurred vision, retinal haemorrhages, "sausage links" on fundoscopy, epistaxis
• Cryoglobulinaemia, Raynaud's, peripheral neuropathy
• Tx: plasmapheresis for hyperviscosity (emergency) → ibrutinib + rituximab

Normal Haemostasis

• Primary: platelet plug formation — vascular injury → collagen exposed → vWF bridges collagen to GPIb → platelet adhesion; ADP/TXA2 → activation → GPIIb/IIIa → aggregation
• Secondary: coagulation cascade → fibrin mesh reinforces platelet plug
• Extrinsic: TF + VII → Xa (PT/INR measures this pathway)
• Intrinsic: XII → XI → IX → X (aPTT measures this pathway)
• Common: X + Va (prothrombinase complex) → II (prothrombin) → IIa (thrombin) → fibrinogen → fibrin → XIII stabilises

Thrombocytopenias

• Decreased production: aplastic anaemia, MDS, marrow infiltration, B12/folate, alcohol
• Increased destruction: ITP, TTP/HUS, DIC, HIT, HELLP
• Sequestration: hypersplenism (spleen can sequester up to 90% of platelet pool)
• Dilutional: massive transfusion

Platelet Disorders

• Glanzmann's thrombasthenia: GPIIb/IIIa defect (no aggregation) → normal count, ↑ BT, no platelet plug, ADP/collagen/thrombin induced aggregation all absent
• Bernard-Soulier syndrome: GPIb defect (no adhesion) → giant platelets, ↑ BT, absent ristocetin-induced aggregation (similar to VWD type 3)
• Platelet storage pool disorders: dense granule (↓ ADP/Ca²⁺) or α-granule deficiencies

Von Willebrand Disease (VWD)

Haemophilia A & B

• A: Factor VIII deficiency; B (Christmas disease): Factor IX deficiency; both X-linked recessive
• Clinical: haemarthroses, muscle haematomas, prolonged bleeding after surgery. Isolated ↑ aPTT (PT normal).
• Severity: mild (5–40% activity), moderate (1–5%), severe (<1%)
• Tx: factor concentrate. DDAVP works for mild A only (releases VIII from endothelium)
• Haemophilia A inhibitors: bypass agents (FEIBA, recombinant FVIIa) or emicizumab (bispecific antibody, bridges IXa and X)

Hereditary Thrombophilia

Disseminated Intravascular Coagulation (DIC)

Labs: ↑ PT, ↑ aPTT, ↑ TT, ↑ D-dimer, ↓ fibrinogen, ↓ Platelets, schistocytes on smear. Fibrinogen is an acute-phase reactant — may be normal-low initially.

Tx: treat underlying cause. Replace: FFP (factors), cryoprecipitate (fibrinogen, XIII, vWF), platelets. Heparin only in chronic DIC (cancer, Trousseau syndrome).

Heparin-Induced Thrombocytopenia (HIT)

TTP (Thrombotic Thrombocytopenic Purpura)

• ADAMTS13 deficiency (<10%) → ultra-large vWF multimers → platelet aggregation in microvessels → microangiopathic haemolytic anaemia (MAHA) + thrombocytopenia
• Acquired TTP: anti-ADAMTS13 autoantibodies (most common). Hereditary TTP (Upshaw-Schulman): congenital ADAMTS13 deficiency.
• ADAMTS13 <10% = diagnostic (normal in HUS)
• Tx: Plasma exchange (PEX) EMERGENTLY — replaces ADAMTS13 + removes antibodies. Add steroids + rituximab (for antibody-mediated). Caplacizumab (anti-vWF nanobody) reduces time to platelet recovery.
• NO platelet transfusions (worsen micro-thrombosis). Avoid if at all possible.

HUS (Haemolytic Uraemic Syndrome)

• Typical HUS: E. coli O157:H7 → Shiga toxin → endothelial damage in kidney → MAHA + thrombocytopenia + acute renal failure (AKF more prominent than in TTP)
• NO antibiotics — increase Shiga toxin release (lyse bacteria → release more toxin)
• ADAMTS13 normal (distinguishes from TTP)
• Atypical HUS (aHUS): complement dysregulation (CFH, CFI, C3, CFB mutations) → eculizumab
• Tx typical: supportive, dialysis if needed. NO PEX (not TTP).

Immune Thrombocytopenia (ITP)

• Anti-platelet antibodies (anti-GPIIb/IIIa or GPIb/IX) → splenic destruction
• Children: often post-viral, self-limiting. Adults: chronic, female predominance.
• Diagnosis of exclusion: isolated thrombocytopenia, normal BM, no splenomegaly
• Tx: Plt >30 + no bleeding → observe. Plt <30 or bleeding:
• 1st line: IV methylprednisolone ± IVIG (IVIG blocks FcR on macrophages)
• 2nd line: rituximab (anti-CD20), splenectomy, TPO-RAs (eltrombopag, romiplostim)
• Emergency (intracranial bleed): IVIG + steroids + platelet transfusion (temporary)

Antithrombotic Agents & Antidotes

Acquired Thrombophilia

• Antiphospholipid syndrome (APS): lupus anticoagulant + anticardiolipin + anti-β2GPI antibodies → thrombosis (arterial + venous) + pregnancy loss. Paradox: ↑ aPTT in vitro (inhibits phospholipid) but PROCOAGULANT in vivo.
• Tx: warfarin (INR 2–3 for VTE; 2.5–3.5 for arterial); aspirin if only obstetric.
• Other: cancer (Trousseau), OCPs (especially Factor V Leiden carriers), nephrotic syndrome (ATIII loss → thrombosis), PNH, hyperhomocysteinaemia