Hematology
8 high-yield topics. Open a topic to review its pearls.
Anemia
Microcytic, normocytic, macrocytic
First Steps
- First test for evaluating anemia: reticulocyte count
- Unexplained iron deficiency: do colonoscopy
Microcytic (MCV <80)
- Iron deficiency: low ferritin (<20 diagnostic), high RDW, pencil cells; associations: PICA, Plummer-Vinson, koilonychia, restless legs
- Thalassemia: target cells, teardrop cells, basophilic stippling; low MCV disproportionate to Hgb, normal RDW
- Sideroblastic: ringed sideroblasts; causes lead, INH, alcohol, copper deficiency
- Lead poisoning: basophilic stippling (old building, gout, headache)
Anemia of Chronic Disease
- Low serum iron, low TIBC, low transferrin saturation, normal/high ferritin
- Bone marrow stores NOT depleted
- Treatment: erythropoietin and iron when symptomatic
- EPO with Hgb >10 increases HTN and CVA risk
Macrocytic (MCV >100)
- B12 deficiency: usually MCV >110, posterior column signs (vibration/proprioception), hypersegmented neutrophils; check MMA level
- Folate deficiency: no neuro symptoms; check homocysteine
- Pernicious anemia: intrinsic factor antibodies, Schilling test
- Myelodysplastic syndrome (MCV 100-110): elderly, cytopenias, Pelger-Huet, ringed sideroblasts
Hemostasis Disorders
Bleeding and hemolytic anemias
Coombs Test
- Direct: patient RBC + anti-IgG/anti-C3 detects antibodies on RBCs
- Warm antibody: IgG, extravascular, idiopathic/drugs/lymphoma → steroids, splenectomy
- Cold antibody: IgM, intravascular, infections (EBV, mycoplasma) → immunosuppressants (NO splenectomy/steroids)
Microangiopathic Hemolytic Anemias
- HUS: young, GI symptoms, renal failure, schistocytes, E. coli O157:H7 — NO antibiotics, supportive
- TTP: fever, low platelets, renal dysfunction, neuro, hemolysis — plasma exchange (platelets contraindicated)
- HELLP: 3rd trimester → deliver baby
Other Hemolytic Anemias
- Hereditary spherocytosis: spectrin deficiency, osmotic fragility test, folic acid + splenectomy
- G6PD deficiency: X-linked, bite cells, oxidative stress (sulfonamides, dapsone, fava beans)
- PNH: dark morning urine, CD55 assay/flow cytometry, splenic thrombosis, → eculizumab
Aplastic Anemia
- Reticulocyte count ~0, hypocellular marrow
- Causes: idiopathic, PNH, radiation, drugs (chloramphenicol, sulfonamides), parvovirus B19
- Parvovirus aplastic crisis in sickle cell: diagnose parvovirus IgM, treat IVIG
- Treatment: BMT (young) or immunosuppressives (older)
Hypercoagulable States
Inherited and acquired thrombophilia
Inherited
- Factor V Leiden: APC resistance, most common inherited disorder
- Prothrombin G20210A
- Protein C/S deficiency: warfarin skin necrosis risk
- Antithrombin III deficiency: heparin resistance
Acquired
- Antiphospholipid syndrome: lupus anticoagulant, prolonged PTT not corrected by mixing
- Malignancy, pregnancy/OCP, immobility, surgery
- Do NOT do hypercoagulable workup for first DVT with known cause
Hemochromatosis
Iron overload
Key Points
- Transferrin saturation >55% (best screening test)
- Ferritin usually >1000
- HFE gene testing if transferrin saturation elevated
- Manifestations: DM (pancreas), hyperpigmentation (skin), cardiomyopathy, abnormal LFTs, hypogonadism, arthropathy (1st MCP)
- Try phlebotomy before chelating agents
Sickle Cell Anemia
Trait, disease, crises
Management
- Most important prognostic factor: level of Hgb F (higher is better)
- Treatment: folic acid; hydroxyurea if >3 crises/year (increases Hgb F)
- Vaccinate: H. flu, meningococcus, pneumovax
- Osteomyelitis: Salmonella
Acute Chest Syndrome
- Chest pain, fever, decreased O2 sat, infiltrate on x-ray
- Failure to respond to antibiotics
- Treatment: exchange transfusion + correct hypoxia
- May require early intubation
Variants
- Trait (Hb AS): Hb S <50%, crisis in severe hypoxia, papillary necrosis
- Disease (Hb SS): Hb S 75-95%, functional asplenia, vaso-occlusive crises
- Hb SC: aseptic necrosis of hip, splenomegaly, target cells
- Exchange transfusion for stroke or operative procedures
Myeloproliferative Disorders
PV, ET, CML, myelofibrosis
Overview
- Polycythemia vera: elevated RBC mass, low EPO, JAK2 mutation, pruritus after bathing; phlebotomy + hydroxyurea
- Essential thrombocytosis: platelets >600K, thrombosis/bleeding risk
- Myelofibrosis: teardrop cells, marrow fibrosis
- CML: Philadelphia chromosome (BCR-ABL), low LAP score, imatinib
Leukemias
Acute and chronic
Acute Leukemias
- AML: Auer rods, myeloperoxidase positive; APL (M3) → DIC risk, ATRA
- ALL: children, TdT positive, CNS involvement, tumor lysis
Chronic Leukemias
- CLL: elderly, smudge cells, hypogammaglobulinemia, warm autoimmune hemolysis
- CML: Philadelphia chromosome, splenomegaly, blast crisis
Transfusion Medicine
Reactions and products
Transfusion Reactions
- Acute hemolytic: ABO incompatibility, fever/flank pain/hypotension — stop transfusion
- Febrile non-hemolytic: most common, cytokines
- IgA deficiency: anaphylaxis risk, give IgA-deficient blood
- TRALI: acute lung injury within 6 hours
- Multiple transfusions: low calcium (citrate)