Path 14 RBC Bleeding Disorders
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| causes of microcytic, hypochromic anemia (MCV<80)? | iron def; alpha- and beta-thalassemia; lead poisoning; sideroblastic anemia
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| causes of megaloblastic anemia? | folate deficiency; B12 deficiency
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| causes of nonhemolytic normocytic, normochromic anemia? | anemia of chronic dz; aplastic anemia; kidney dz
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| causes of intrinsic hemolytic anemia? | hereditary spherocytosis; G6PD def; pyruvate kinase def; SCA; HbC defect
parxoysmal nocturnal hemoglobinuria
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| causes of extrinsic hemolytic anemia? | autoimmune; microangiopathic (eg DIC, TTP-HUS); infectious
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| causes of intravascular hemolysis? | paroxysmal nocturnal hemoglobinuria; autoimmune (cold agglutinins); mechanical (AO stenosis, prosthetic valve)
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| causes of extravascular hemolysis? | Hereditary spherocytosis; G6PD def; Pyruvate kinase def; SCA; HbC defect; Autoimmune (warm agglutintins); Microangiopathic (eg DIC, TTP-HUS)
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| Types of normochromic, normocytic anemias? | Nonhemolytic; Intrinsic hemolytic; Extrinsic hemolytic; Intravascular hemolysis
Extravascular hemolysis
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| why does acute blood loss result in anemia? | blood volume lost is restored by intravascular shift of water from interstitial fluid compartment, resulting in hemodilution and lowering of HCT
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| What changes in peripheral blood are seen after significant blood loss? | low HCT; reticulocytosis; leukocytosis; thrombocytosis
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| which anemia is characterized by splenomegaly and jaundice? | extravascular hemolytic anemia
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| which anemia is manifested by hemoglobinemia, hemoglobinuria, hemosiderinuria, and jaundice? | intravascular hemolytic anemia
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| common non-hematologic complication of chronic hemolytic anemia | pigment gallstones
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| normocytic, normochromic anemia w/ reticulocytosis | hemolytic anemia
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| anemia resulting in hemosiderosis of spleen, liver, and bone marrow | hemolytic anemia
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| most prevalent inheritance pattern in spherocytosis? | autosomal dominant (75%)
(25% have more severe form caused by two different defects)
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| PBS shows small, hyperchromic RBCs lacking central pallor. Dx? | spherocytosis
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| Howell-jolly bodies indicate what? | splenic dysfunction or splenectomy (esp in setting of spherocytosis)
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| what causes spherocytosis? | mutations lead to insufficiency of RBC membrane components and progressive loss of membrane fragments
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| what are the RBC membrane skeletal components? | ankyrin, band 3, spectrin, band 4.2
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| what usually triggers aplastic crises in spherocytosis? | parvovirus infxn (kills RBC progenitors)
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| treatment for spherocytosis? | splenectomy and/or transfusion
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| CBC findings in spherocytosis? | anemia, inc MCHC, inc RDW
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| abnormalities in hexose monophosphate shunt or glutathione metabolism are the basis of what disease? | G6PD-deficiency (hemolysis)
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| inheritance pattern of G6PD-def? | X-linked (males at higher risk)
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| PBS shows RBCs with Heinz bodies and bite cells. Dx? | G6PD-def
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| what triggers hemolysis in G6PD-deficient patients? | oxidant stress, e.g. infxn, drugs (primaquine, chloroquine, sulfonamides), fava beans
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| in what diseases are Heinz bodies found? | G6PD-def, alpha thalassemia
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| what causes Heinz bodies? | exposure of RBC to high levels of oxidants cross-links globin chains which become denatured
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| what causes bite cells? | macrophages in splenic cords attempt to remove Heinz bodies and damage membrane
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| why is spherocytosis self limited? | only old RBCs are at risk for lysis
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| disease associated with a mutation that replaces glutamate in beta globin with valine | sickle cell disease
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| sickle cell trait vs. disease? | heterozygosity for HbS
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| composition of HbA? | alpha2beta2
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| composition of HbA2? | alpha2 delta2
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| composition of HbF? | alpha2 gamma2
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| composition of HbS? | alpha2 beta(sickle)2
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| what disorders confer immunity to malaria? | sickle cell trait, G6PD-deficiency
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| when does SCA start in child that has inherited the disease? | 6-7 mo (persistence of HbF)
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| what other disease, when coexistent with homozygous HbS, leads to milder disease? | a-thalassemia
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| "crew cut" skull x-ray from marrow expansion from inc erythropoiesis? | SCA and thalassemias
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| what precipitates sickling in SCA? | low O2 or RBC dehydration
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| complications in SCA homozygotes? | - aplastic crisis (B19 infxn)
- Autosplenectomy --> infxn w/ encapsulated organisms
- salmonella osteomyelitis
- vaso-occlusive crises
- renal papillary necrosis
- splenic sequestration crisis
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| tx for SCA? | hydroxyurea (inc HbF), BM txp
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| what causes target cells? | RBC dehydration
(SCA, HbC dz, asplenia, liver dz, thalassemias)
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| what causes autosplenectomy in SCA? | chronic erythrostasis leads to splenic infarction, fibrosis and shrinkage
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| what is the genetic difference in the alpha and beta chains for HbA? | α-globins are encoded by a pair of genes on chromosome 16 whereas β-globins are encoded by a single gene on chromosome 11
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| cause of anemia prevalent in Mediterranean populations | β thalassemia
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| most common genetic cause of β+ thalassemia | promoter region mutations
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| most common genetic cause of β0 thalassemia | chain terminator mutations
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| genotype of thalassemia major? | β0/β0 (HbA absent), β+/β+ or β0/β+ (HbA reduced)
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| genotype of thalassemia minor? | heterozygous carriers of one β+ or β0 allele
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| how does α-thalassemia manifest in newborns? | excess unpaired γ-globin (from HbF) clump together forming Hb-Barts leading to hydrops fetalis (fatal)
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| how does α-thalassemia manifest in older children and adults? | excess unpaired β-globin (from HbA) forms HbH tetramers --> HbH disease (tissue hypoxia and moderately severe anemia)
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| in what population is HbH disease common? | Asians
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| genotype of silent carrier of α-thalassemia? | -/α α/α
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| genotype of α-thalassemia trait? | -/- α/α (Asian), -/α -/α (African)
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| genotype of HbH disease? | -/- -/α
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| genotype of hydrops fetalis? | -/- -/- (no α alleles)
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| pathogenesis of paroxysmal nocturnal hemoglobinuria? | acquired mutations in phosphatidylinositol glycan complementation group A gene (PIGA - makes surface proteins that inhibit complement-mediated lysis) --> complement lysis of RBCs, PLTs, WBCs
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| why is PNH more active at night? | low resp --> mild acidosis --> increase activity of complement
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| abnml lab finding in PNH? | hemosiderinuria
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| difference between direct and indirect Coombs test? | Direct: anti-Ig Ab added to pt's RBCs clumps if serum has anti-RBC surface Ig
Indirect: normal RBCs added to pt's serum, clump if serum has anti-RBC surface Ig
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| anemia characterized by IgG-mediated membrane damage of RBCs; esp assoc'd with α-methyldopa, and large IV doses of penicillins and cephalosporins | warm agglutinin autoimmune hemolytic anemia
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| anemia associated with IgM-mediated hemolysis after infxn by Mycoplasma pneumoniae, EBV, CMV, influenza, HIV | cold agglutinin autoimmune hemolytic anemia
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| causes of microangiopathic hemolytic anemia? | prosthetic valves or AS; DIC, TTP-HUS; SLE
malignant HTN
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| schistocytes, burr cells, helmet cells and triangle cells on PBS indicate what class of anemias? | microangiopathic hemolytic anemia
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| causes of microcytic, hypochromic anemia? | iron def; thalassemias; lead poisoning; sideroblastic anemia
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| anisopoikilocytosis, low retic, large, hyper-segmented neutrophils. Dx? | megaloblastic anemia
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| pathogenesis of pernicious anemia? | autoimmune gastritis --> loss of parietal cells --> dec IF --> dec abs of B12 --> folate trapped in intermediate form --> dec DNA synthesis
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| why are both B12 and folate essential for DNA synthesis? | B12 takes Me from N-methylFH4 and turns homocysteine into methionine and frees folate to convert dUMP to dTMP --> DNA
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| causes of B12 deficiency? | malnutrition (alcoholics); malabsorption (Crohns); pernicious anemia;Diphyllobothrium latum infxn
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| causes of neuro sxs of B12 def? | B12 used to convert methylmalonyl CoA to succinyl CoA; deficiency --> methylmalonate and propionate buildup --> incorporation of abnml fatty acids into neuronal lipids
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| findings in B12 def? | -inc homocysteine -inc methymalonic acid -hypersegmented neut
-glossitis
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| causes of folate def? | - malnutrition (alcoholics) - malabsorption- impaired metabolism (methotrexate, TMP) - inc requirement (preg, hemolytic anemia)
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| difference in lab findings of B12 and folate def? | B12 = inc Hcy and methylmalonate
Folate = inc Hcy but normal methylmalonate
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| what drugs interfere with the absorption of folate? | phenytoin and oral contraceptives
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| what drugs interfere with the metabolism of folate? | folic acid antagonists (methotrexate, TMP)
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| what stain detects hemosiderin deposits? | Prussian blue stain
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| function of hepcidin? | inhibits iron transfer from enterocyte to plasma; suppresses iron release from macrophages
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| MCC of iron deficiency in developed countries? | GI blood loss
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| what causes koilonychia, alopecia, atrophy of tongue and gastric mucosa, pica, and intestinal malabsorption? | severe, chronic iron deficiency
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| Plummer-Vinson syndrome? | esophageal webs, microcytic hypochromic anemia, and atrophic glossitis
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| iron deficiency anemia: serum iron? TIBC? Ferritin? % sat? | iron LOW
TIBC HIGH
Ferritin LOW
% sat VERY LOW
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| ACD: serum iron? TIBC? Ferritin? % sat? | iron LOW
TIBC LOW
Frtn HIGH
% sat NORMAL
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| Hemochromatosis: serum iron? TIBC? Ferritin? % sat? | iron HIGH
TIBC LOW
Frtn HIGH
%sat VERY HIGH
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| Pregnancy/OCP use: serum iron? TIBC? Ferritin? % sat? | iron NORMAL
TIBC HIGH
Frtn NORMAL
%sat LOW
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| causes of ACD? | - chronic microbial infxn (osteomyelitis, bact endocarditis, lung abscess)
- chronic immune disorders (RA, regional enteritis)
- Neoplasms (lung and breast carcinoma, Hodgkin lymphoma)
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| pathogenesis of ACD? | inflammatory mediators (IL-6) stimulate inc hepatic production of hepcidin which causes macrophage sequestration of iron;
No retics d/t low EPO levels
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| MCC of aplastic anemia? | exposure to chemicals and drugs (cancer chemo, benzene, chloramphenicol, gold salts)
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| Fanconi anemia? | autosomal recessive, defects in multiprotein complex required for DNA repair lead to aplastic anemia
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