RBC disorders

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RBC disorders
2013-04-02 20:50:54

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  1. Anemia
    basic principles
    Reduction in circulating red blood cell (RBC) mass

    • Presentation: sx of hypoxia
    • 1. Weakness, fatigue, dyspnea
    • 2. Pale conjunctiva and skin
    • 3. Headache and lightheadedness
    • 4. Angina

    Hemoglobin (Hb), hematocrit (Hct), and RBC count are surrogates for RBC mass. Hb <13.5g/dL in men; <12.5g/dL in women [concentrations]

    • -Microcitic: MCV <80
    • -Normocytic: MCV between 80 and 100
    • -Macrocytic: MCV >100
  2. Microcytic anemia
    Puny TICS

    • -Pernicious anemia
    • -Thalassemia
    • -Iron deficiency anemia
    • -Chronic disease (anemia of chronic disease)
    • -Sideroblastic anemia

    • Due to decreased production of hemoglobin
    • RBC progenitors (erythroblasts) go through an "extra" division to maintain hemoglobin concentration

    • -Hemoglobin = heme + goblin
    • -Heme = iron + protoporphyrin
  3. Iron deficiency anemia
    Decreased iron --> decreased heme --> decreased hemoglobin --> microcytic anemia

    • Epidemiology
    • -Most common type of anemia
    • -most common nutritional deficiency in the world (1/3 world wide)

    • Fe physiology:
    • Absorption occurs in the duodenum (enterocytes transport iron across membrane into blood via ferroportin). Storage in the liver and bone marrow macrophages (stored intracellular iron is bound to ferritin).

    • Labs: TIBC is opposite ferritin 
    • -serum iron
    • -total iron-binding capacity (TIBC) - measure of transferrin
    • -% saturation - percentage of transferrin molecules that are bound by iron (normal is 33%)
    • -Serum ferritin - iron stores in macrophages and in liver

    • Etiology:
    • 1. Infants - breast feeding (human milk is low in Fe)
    • 2. Children - poor diet
    • 3. Adults - peptic ulcer disease and menorrhagia (or pregnancy)
    • 4. Elderly - colon polyps/carcinoma (western world); hook worm (developing world)
    • 5. Other - malnutrition, malabsorption, gastrectomy (acid needed to absorb iron: Fe2+ goes in2 the body...Fe3+ does not get absorbed)

    • Stages of iron deficiency:
    • 1. Storage of iron is depleted
    • 2. Serum iron is depleted
    • 3. Normocytic anemia - bone marrow makes fewer, but normal RBCs
    • 4. Microcytic, hypochromic anemia (expanded central palor)

    • Presentation/labs
    • -anemia, koilonychia (spoon shaped nails), pica
    • -increased RDW
    • - decreased ferritin; increased TIBC; decreased serum iron; decreased % saturation
    • -increased free erythrocyte protoporphyrin (FEP)
  4. Anemia of chronic disease
    Anemia associated with chronic inflammation or cancer

    -Most common type of anemia in hospitalized patients

    • Pathophysiology:
    • -chronic disease produces acute phrase reactants, including hepcidin, which sequesters iron in storage sites by...
    • 1. limiting iron transfer from macrophages to erythroid precursors
    • 2. suppressing erythropoietin (EPO) production
    • -Decrease in available iron --> decrease heme --> decrease hemoglobin --> microcytic anemia

    • Lab findings:
    • -increase ferritin, decrease TIBC, decrease serum iron, and decrease % saturation
    • -increase free erythrocyte protoporphyrin (FEP)

    • Tx:
    • -treat underlying cause
    • -exogenous EPO can be useful in pts with cancer

    anemia of chronic disease goes through same stages as iron deficient anemia (normocytic anemia followed by microcytic anemia)
  5. Sideroblastic anemia
    Anemia due to defective protoporphyrin synthesis --> decreased heme...

    • Protoporphyrin synthesis:

    • Pathophysiology:
    • 1. Congenital ALAS defect (rate limiting enzyme)
    • 2. Alcoholism - mitochondrial poison --> decreased production of protoporphyrin
    • 3. Lead poisoning - inhibits ALAD and ferrochelatase
    • 4. Vit B6 deficiency (Pyridoxine) - cofactor required for ALAS. side effect of isoniazid tx for TB
    • Lab:
    • -increase ferritin, decrease TIBC, increase serum iron, and increase % saturation
    • -iron overload state

    • Pathology:
    • ringed sideroblasts
    • -iron in the mitochondria can't escape; mitrochondria incircle the nucleus
  6. Thalassemia
    Anemia due to decreased synthesis of the globin chains of hemoglobin

    Inherited mutation - carriers are protected against plasmodium falciparum malaria

    • Physiology:
    • Hemoglobin
    • - HbF (α2γ2)
    • - HbA (α2β2)
    • - HbA22δ2)

    • α-Thalassemia
    • - 4 alpha genes are present on chromosome 16
    • --------α----α-------
    • --------α----α-------

    • 1. One gene deleted - asymptomatic
    • 2. Two genes deleted - mild anemia with increased RBC count; cis deletion is associated with an increaed risk of severe thalassemia in offspring - cis is seen in Asians, trans is in Africans
    • 3. Three genes deleted - severe anemia; β chains form tetramer (HbH = β2β2) that damages RBCs
    • 4. Four genes deleted - lethal in utero (hydrops fetalis). γ chains form tetramer (Hb Barts) that damages RBCs

    • β- thalassemia
    • -african and mediterranean descent
    • - 2 beta genes are present on chromosome 11; mutations result in absent (βo) or diminished (β+) production of the β-globin chain

    • β-thalassemia minor (β/β+) is the mildest form of disease; usually asymptomatic with increase in RBC count
    • -microcytic, hypochromic RBCs and target cells
    • -electrophoresis shows slightly decreased HbA with increased HbA2 and HbF

    • β-thalassemia major (βoo) is the most severe form of the disease; severe anemia within months; high HbF at birth is temporarily protective
    • -α tetramers  aggregate and damage RBCs, ineffective erythropoiesis and extravascular hemolysis
    • -expansion of hematopoiesis into skul and facial bones
    • -extramedullary hematopoiesis with HSM
    • -risk of aplastic crisis with parvovirus B19 infection of erythroid precursors

    • Tx:
    • -chronic transfusions are necessary; secondary hemochromatosis

    Smear shows microcytic, hypochromic RBCs with target cells and nucleated RBCs

    Electrophoresis shows little to no HbA with increased HbA2 and HbF
  7. Macrocytic anemia
    Anemia with MCV > 100 most commonly due to folate or vitamin B12 deficiency (megaloblastic anemia)... precursors go through too few divisions

    • -Folate/VitB12 are necessary for synthesis of DNA precursors

    Methyl group gets passed from Folate to B12 then to Homocysteine (which becomes methyanine)

    • Megaloblastic anemia:
    • -other rapidly dividing cells get big
    • -hypersegmented neutrophils (>5 lobes)

    • Other causes of macrocytic anemia...
    • -Folate deficiency
    • -Vitamin B12 deficiency
    • -Liver disease
    • -Increased reticulocytes
    • -drug induced (methotrexate, 5-FU)
    • -MDS (myelodysplastic syndrome
  8. Folate Deficiency
    Macrocitic (megaloblastic) anemia

    Dietary sources: green vegetables, some fruits

    Absorption: jejunum

    Body stores: minimal; deficiency develops in months

    • Etiology:
    • -poor diet (alcoholics, elderly)
    • -increased demand (pregnancy, cancer, hemolytic anemia)
    • -folate antagonists (methotrexate)

    • Labs:
    • -Macrocytic RBCs, hypersegmented neutrophils (>5 lobes)
    • -Glossitis - inflammation of the tongue
    • - ↓ serum folate
    • - ↑ serum homocysteine (increases risk for thrombosis)
    • - Normal methylmalonic acid

    *B12 needed to convert MMA to SucCoA
  9. Vitamin B12 deficiency
    Macrocytic (megaloblastic) anemia

    Less common than folate deficiency: takes years to develop (large hepatic stores of vitamin B12)

    • Etiology:
    • -Pernicious anemia is the most common cause (Autoimmune destruction of parietal cells --> ↓ IF
    • *Parietal cells: Pink cells, Proton pump, Pernicious anemia

    • -pancreatic insufficiency
    • -damage to the terminal ileum (Crohn disease or Diphyllobothrium latum)
    • -dietary deficiency is rare, except in vegans

    • Clinical findings/Labs:
    • -Macrocytic RBCs with hypersegmented neutrophils
    • -Glossitis
    • -Subacute combined degeneration of the spinal cord (MMA build up in the myelin of the spinal cord). Impairs proprioception and vibratory censation and spastic paresis
    • -↑ MMA (methylmalonic acid)
    • -↑ homocysteine, increases risk of thrombosis
    • -↓ serum vitamin B12

    **B12 is involved in conversion of MMA to SucCoA
  10. Normocytic anemia
    MCV is between 80 and 100

    • Etiology:
    • -↑ peripheral destruction (hemolysis - extravascular or intravascular)
    • - underproduction
    • *Reticulocyte count distinguishes between these two etiologies

    • Common causes:
    • -Hemolytic anemia
    • -Sickle cell anemia
    • -Anemia of chronic disease
  11. Reticulocytes
    • Young RBCs released from the bone marrow

    • Normal count: 1-2%
    • -RBC's lifespan is 120 days; 1-2% RBCs are removed from circulation and replaced by reticulocytes daily

    • Normal BM: will increase reticulocyte count to >3% in response to anemia
    • *must correct for loss of RBCs
    • Corrected RC = RC x Hct/45

    Normal BM will have Corrected RC >3% in response to anemia; otherwise, underproduction
  12. Hemolysis
    Peripheral RBC destruction

    • I. Extravascularreticuloendothelial system (Macrophages of the spleen, liver, and lymph nodes)
    • - RBC → hemoglobin
    • - heme → iron + protoporphyrin
    • - iron is recycled; protoporphyrin → unconjugated bilirubin (which gets bound to albumin and delivered to liver for congucation)
    • Labs:
    • -Anemia with splenomegaly, jaundice due to unconjugated bilirubin, increased risk for bilirubin gallstone
    • -Marrow hyperplasia with corrected RC > 3%

    • II. Intravascular - within the vessels
    • Labs:
    • - Hemoglobinemia
    • - Hemoglobinuria
    • - Hemosiderinuria - renal tubular cells pick up some of the hemoglobin; accumulates as hemosiderin... cells shed and results in hemosiderinuria
    • - Decreased serum haptoglobin (scavenger of free hemoglobin)
  13. Normocytic anemias
    with extravascular hemolysis
    • Hereditary spherocytosis
    • Sickle cell anemia
    • Hemoglobin C
  14. Hereditary spherocytosis
    • - inherited defect of RBC cytoskeleton-membrane tethering proteins
    • -most commonly involves spectrin, ankyrin, or band 3.1

    • Pathophysiology: membrane "blebs" are formed and lost over time
    • -results in round cells (spherocytes) that are consumbed by splenic macrophages

    • Clinical/lab findings:
    • -Spherocytes, loss of central pallor
    • -↑ RDW and ↑ mean corpuscular hemoglobin concentration (MCHC)
    • -Splenomegaly, jaundice with unconjugated bilirubin, increase risk for bilirubin gallstones
    • -increased risk for aplastic crisis with parvovirus B19 infection

    Dx: osmotic fragility test... increased spherocyte fragility in hypotonic solution (not able to expand)

    • Tx: splenectomy; anemia resolves, but spherocytes persist
    • -Howell-Jolly bodies emerge on blood smear (spleen used to remove these nuclear fragments)
  15. Sickle cell anemia
    • Autosomal recessive mutation in β chain of hemoglobin
    • -Glutamic acid (hydrophilic) → Valine (hydrophobic)

    • Epidemiology: gene is carried by 10% of individuals of African descent
    • -Protective against falciparum malaria

    • Pathophysiology: two abnormal β genes results in >9-% HbS in RBC
    • -HbS polymerizes when deoxygenated; polymers aggregate into needle-like structures, resulting in sickle cells (reversible)

    • -Risk factors: hypoxemia, dehydration, acidosis
    • -HbF is protective in first few months. Tx with hydroxyurea increases levels of HbF

    • Complications: RBC membrane damage
    • -Extravasculat hemolysis
    • -Intravascular hemolysis (minimal)
    • -Erythroid hyperplasia (expansion of hematopoiesis into skull and facial bones)
    •      - Extramedullary hematopoiesis with hepatomegaly
    •     - Risk of aplastic crisis with Parvovirus B19

    • Irreversible sickling: vaso-occlusion
    • -Dactylitis (swollen hands and feet)
    • -Autosplenectomy - shrunken, fibrotic spleen (increased risk of infection with encapsulated organisms like S. pneumo, H. influenzae). Howell-Jolly bodies
    • -Acute chest syndrome - vaso-occlusion in pulmonary microcirculation (most common cause of death in adult patients)
    • -Pain Crisis
    • -Renal papillary necrosis - hematuria nd proteinuria

    • Lab findings:
    • -Sickle cells, target cells (not in trait)
    • -Metabisulfite screen - causes cells to sickle with any amount of HbS

    • Sickle cell trait - one mutated and one normal β chain
    • -Asymptomatic; need > 50% HbS within RBCs for sickling
  16. Hemoglobin C
    Autosomal recessive mutation in β chain of hemoglobin

    • -Glutamic acid is replaced by lysine
    • (less common than SCD)

    Presentation: mild anemia with extravascular hemolysis

    • HbC crystals

    "LyCne HbC crystals"
  17. Normocytic anemias
    with intravascular hemolysis
    • Paroxysmal Nocturnal hemoglobinuria (PNH)
    • Glucose-6-phosphate dehydrogenase (G6PD) deficiency
    • Immune hemolitic anemia (IHA)
    • Microangiopathic hemolytic anemia (MAHA)
    • Malaria
  18. Paroxysmal nocturnal hemoglobinuria 
    • Acquired defect in myeloid stem cell resulting in absent glycosylphosphatidylinositol (GPI) which makes cells susceptible to destruction by complement
    • -anchoring protein for Decay accelerating factor (DAF) and MIRL; DAF protects against complement-mediated damage by inhibiting C3 convertase

    • Pathophysiology:
    • -decreased respirations at night (sleep) cause ↑CO2 → respiratory acidosis → Activates compliment
    • -Destruction of RBCs, WBCs, and platelets

    • Dx:
    • Sucrose test - sucrose activates compliment
    • -flow cytometry for CD55 (DAF)

    • Mortality: main cause of death is thrombosis of hepatic, portal, or cerebral veins
    • -destroiyed platelets release cytoplasmic contents, inducing thrombosis

    • Complications:
    • -iron deficiency anemia
    • -Acute myeloid leukemia (AML), develops in 10% of patients
  19. Glucose-6-phosphate dehydrogenase (G6PD) deficiency
    X-linked recessive disorder resulting in reduced half-life of G6PD; cells susceptible to oxidative stress

    • Pathophysiology: ↓G6PD → ↓NADPH → ↓reduced glutathione → oxidative injury by H2O2 → intravascular hemolysis
    • -Glutathion (GSH) protects against oxidative stress by neutralizing H2O2, but needs to be reduced after the process
    • -Oxidized glutathion is reduced by NADPH (a bi-product of G6PD)

    • Variants
    • 1. African variant - mildly reduces half-life →mild intravascular hemolysis
    • 2. Mediterranean variant - markedly reduced half-life
    • -both populations: carriers are protective against falciparum malaria

    • Findings:
    • Oxidative stress (infections, drugs, fava beans) precipitates Hb as Heinz bodies → splenic macrophages remove → Bite cells
    • →predominantly intravascular hemolysis

    Presentation: back pain hours after exposure to oxidative stress, hemoglobinuria
  20. Immune hemolytic anemia (IHA)
    Antibody mediated (IgG or IgM) destruction of RBCs

    • IgG-mediated →extravascular hemolysis
    • -IgG binds RBCs in warm temperature of central body (warm agglutinin)
    • -membrane is consumed by splenic macrophages → spherocytes
    • -Associated with SLE, CLL, drugs
    • -Tx: stop offending drug, steroids, IVIG, splenectomy (last resort)

    • IgM-mediated → intravascular hemolysis
    • -IgM binds RBCs and fixes complement in cold temperature of extremities (cold agglutinin)
    • -Associated with Mycoplasma pneumoniae and infectious mononucleosis

    • Dx: Coombs test
    • 1. Direct Coombs test: Are the patient's RBCs bound by IgG?
    • -Anti-IgG is added to patient's RBCs: agglutination = positive
    • 2. Indirect Coombs test: Are there Ab in the patient's serum?
    • -Test RBCs and Anti-IgG are added to the patients serum: agglutination = positive
  21. Microangiopathic hemolytic anemia (MAHA)
    Intravascular hemolysis resulting from vascular pathology; RBCs are destroyed as they pass through circulation

    -Iron deficiency anemia occurs with chronic hemolysis

    • Etiology:
    • - TTP [ADAMTS13]
    • - HUS [e. coli 015787]
    • - DIC [platelet-thrombin]
    • - HELLP [pregnant women]
    • - prosthetic heart valves
    • - aortic stenosis

    Blood smear: schistocytes ("helmet cells")
  22. Malaria
    • Infection of RBCs and liver with Plasmodium; transmitted by the female Anopheles mosquito

    • Anemia:
    • -RBCs rupture as part of the Plasmodium life cycle, resulting in intravascular hemolysis
    • -Spleen consumes some infected RBCs (mild extravascular hemolysis with splenomegaly)

    Fever: Falciparum is daily; vivax and ovale is every other day
  23. Anemia due to underproduction
    Decreased production by bone marrow: low corrected reticulocyte count

    • Etiologies:
    • 1. Causes of microcytic and macrocytic anemia
    • 2. Renal failure - low EPO
    • 3. Damage to bone marrow precursors

    • Specifics:
    • -Parvovirus B19
    • -Aplastic anemia
    • -Myelophthisic process
  24. Parvovirus B19
    Infects progenitor red cells; halts erythropoiesis → significant anemia in pts with preexisting marrow stress

    Tx: supportive; self-limited
  25. Aplastic Anemia
    Damage to hematopoietic stem cells → pancytopenia with low RC

    • Etiology:
    • -drugs, chemicals, viral infections, autoimmune damage

    • Bx: empty, fatty marrow

    • Tx:
    • -transfusions
    • - marrow-stimulating factors (EPO, GM-CSF, G-CSF)
    • -Immunosuppression may be helpful in some idiopathic cases
    • -May require bone marrow transplantation as a last resort
  26. Myelophthisic process
    Pathologic process (metastatic cancer) that replaces bone marrow; hematopoiesis is impaired

    → pancytopenia
  27. First aid...