Introduction To Anemias PDF

INTRODUCTION TO ANEMIAS Block: Foundations Block Director: James Proffitt, PhD Session Date: Tuesday, August 06, 2024 Time: 8:00 am - 9:30 am Instructor: Candace Reveles, MD Department: Department of Pathology Email: [email protected]...

INTRODUCTION TO ANEMIAS Block: Foundations Block Director: James Proffitt, PhD Session Date: Tuesday, August 06, 2024 Time: 8:00 am - 9:30 am Instructor: Candace Reveles, MD Department: Department of Pathology Email: [email protected] INSTRUCTIONAL METHODS Primary Method: IM13: Lecture ☐ Flipped Session ☐ Clinical Correlation Resource Types: RE18: Written or Visual Media (or Digital Equivalent) INSTRUCTIONS These lectures will focus on various aspects of classification, clinical presentation, and laboratory diagnosis of various types of anemia. Some aspects of the topics covered here such as complete blood cell analysis, peripheral blood morphologic abnormalities, pathophysiology, clinical presentation and diagnosis have either been already been introduced in previous lectures or will be discussed in great details in future lectures. The lectures intend to bring concepts and reinforce and solidify your knowledge on such important aspects of anemia and expand beyond the topics that have already been discussed. READINGS Kumar V, A. A., Aster JC (2021). Anemia section in Red Blood Cells and Bleeding Disorders. Robbins and Cotran Pathologic Basis of Disease. R. Cotran. Philadelphia, Elsevier: 635-672. LEARNING OBJECTIVES 1. Define anemia with its signs and symptoms 2. Describe the approach to anemia classification 3. Become familiar with the diagnostic tests in work up of a patient with anemia a. Red cell incises b. Reticulocyte count and advanced red cell parameters c. Peripheral blood smear assessment 4. Describe the morphologic findings and diagnostic work up of: a. Anemia of inflammation b. Thalassemia and hemoglobinopathies c. Hemolysis, immune and non-immune mediated hemolysis d. Anemia due to RBC membrane structural defects and enzyme defects CURRICULAR CONNECTIONS Below are the competencies, educational program objectives (EPOs), course objectives, session learning objectives, disciplines and threads that most accurately describe the connection of this session to the curriculum. Block: Foundations | REVELES [1 of 10] INTRODUCTION TO ANEMIAS Related Related Competency\EPO Disciplines Threads COs LOs CO-02 LO-01 MK-05: The altered Pathology N/A structure and function Hematology (pathology & pathophysiology) of the body/organs in disease CO-02 LO-02 MK-05: The altered Pathology N/A structure and function Hematology (pathology & pathophysiology) of the body/organs in disease CO-02 LO-03 MK-05: The altered Pathology N/A structure and function Hematology (pathology & pathophysiology) of the body/organs in disease CO-02 LO-04 MK-05: The altered Pathology N/A structure and function Hematology (pathology & pathophysiology) of the body/organs in disease NOTES ANEMIA Definition: Anemia is the most common disorder of blood. It is defined as reduction of total circulating red cell mass leading to reduced oxygen-carrying capacity and tissue hypoxia. It can occur when there is decrease of total number of red blood cells (RBC), amount of hemoglobin in the circulation or circulating red blood cells mass. Physiologic compensatory mechanisms for anemia: 1. Increasing cardiac output; patients with limited cardiac reserve (heart failure, coronary artery disease) may experience anemia at higher hemoglobin concentration as compared to healthy individuals. 2. Increasing plasma volume; allows remaining RBCs to move more efficiently due to decrease viscosity. 3. Increasing RBC 2,3-diphosphoglycerate (2,3-DPG) which results in diminished oxygen affinity for hemoglobin which results in more oxygen delivery to tissues. Classification of Anemias 1. Morphologic classification, based on red blood cell size: a) Microcytic: i. Defect of hemoglobin synthesis b) Macrocytic: i. Megaloblastic: B12, folate, drug-induced ii. Non-megaloblastic: alcohol, liver disease or hypothyroidism Block: Foundations | REVELES [2 of 10] INTRODUCTION TO ANEMIAS c) Normocytic: anemia of inflammation, acute onset of hemolysis or blood loss, chronic kidney disease 2. Pathophysiologic classification: a) Increase RBC loss: i. Hemorrhage, external or internal ii. Decreased red cell survival, hemolysis (immune, microangiopathic, intrinsic red cell defects) b) Impaired red cell production (hypoplastic): i. Stem cell (acute leukemia, myelodysplastic syndrome, aplastic anemia) ii. Nutritional deficiency (iron, B12, folate, copper) iii. Toxins/drugs (lead) iv. Lack of growth factors (erythropoietin) v. Myelophthisic process (metastatic cancer, infection, bone marrow necrosis) First Aid for the USMLE Step 1 2020 First Aid for the USMLE Step 1 2020 There is substantial overlap between various types of anemia, both morphologically and in terms of pathophysiology. A combination of both approaches is necessary to arrive at an accurate diagnosis. Block: Foundations | REVELES [3 of 10] INTRODUCTION TO ANEMIAS Laboratory Evaluation of Anemia Should focus on (1) determining whether anemia is present and (2) identifying the underlying cause 1. Complete Blood Count (CBC): includes red and white blood cell and platelet counts hemoglobin, hematocrit and RBC indices: a. Hemoglobin (Hb g/dL): main component of RBC b. Hematocrit (Hct %): packed red cell volume c. Red blood cell indices: Mean Cell Volume (MCV fL): the average volume of RBC Mean Cell Hemoglobin (MCH pg): Hb content (mass) of Hb in average RBC Mean Cell Hemoglobin Concentration (MCHC g/dL): average concentration of Hb in a given volume of packed RBCs. Red blood cell distribution with (RDW): coefficient of variation of RBC volume. 2. Reticulocytes: immature non-nucleated RBC that contain RNA; Reflect the bone marrow proliferative capacity: i. Percent of RBC: when expressed as % it may overestimate the red cell production ii. Absolute number: more adequate representation of bone marrow production iii. Immature reticulocyte fraction (IRF %) iv. Reticulocyte Hb concentration (RET-He pg) – reflects availability of functional iron 3. Review of peripheral blood smear: a. Provides key RBC information to create differential diagnosis of anemia i. Shape (biconcave, irregular) ii. Size (microcytic, normocytic, macrocytic) iii. Color (hypo or normochromic) iv. Inclusions (Howell-Jolly bodies, malaria parasites) v. Arrangement 4. Additional studies: a. Special stains: Heinz bodies, supravital stain highlight inclusion bodies composed of denatured Hb b. Complete metabolic panel (CBC) and liver function tests (LFTs) c. Iron studies: serum iron, % transferrin saturation or total iron binding capacity (TIBC), ferritin, vitamin B12, and folate d. Haptoglobin: produced by liver to clear free hemoglobin e. Direct antiglobulin test (Coombs test): antibodies bound to the RBC membrane f. Hemoglobin electrophoresis: measures different types of hemoglobins in the RBC g. Genetic testing: hereditary anemias Block: Foundations | REVELES [4 of 10] INTRODUCTION TO ANEMIAS Morphologic findings and diagnostic work up of anemia Anemia of inflammation: Commonly seen in hospitalized patients May mimic iron deficiency anemia Often associated with chronic infections (osteomyelitis, bacterial endocarditis, lung abscess), chronic kidney disease, immune disorders (rheumatoid arthritis, systemic lupus), or neoplasms (lymphomas, carcinomas) Clinical presentation: Symptoms associated with underlying disease predominate and anemia (usually mild). Labs: normocytic, normochromic or microcytic, hypochromic anemia with low reticulocyte count and ⇩ RET-He along with ⇩ serum iron, ⇩TIBC, ⇧ iron stores and ⇧ ferritin. Hepcidin is a major iron transport modulator and plays a key role in iron metabolism. High levels of IL-1, TNF-α, and interferon-γ and other inflammatory cytokines increase hepcidin synthesis by the liver. Hepcidin binds ferroportin on the intestinal mucosal cells and macrophages and inhibits iron release for heme synthesis leading to functional iron deficiency Other contributing factors: ⇩ erythropoietin levels, impaired iron transport; probably due to a defect in the ability to release iron from the storage pool Treatment: treat the underlying disease; recombinant erythropoietin may be needed. Hemoglobinopathies and thalassemia: Sickle cell disease: homozygous point mutation of the β globin gene leading to a single amino acid substitution of valine for glutamine. HbS polymerizes and crystallizes leading to characteristic sickle shape of the RBCs. HbS polymerization is initially reversible with re-oxygenation, but with repeated cycles of sickling, the damage becomes irreversible. This leads to secondary membrane damage, inflexibility, hemolysis and vasoocclusive disease. Factors precipitating sickling: ⇩ O2 saturation, high altitude, acidosis, infections. Newborns have high concentration of HbF (2α2γ chains) and low HbS, so sickling is not seen until fetal hemoglobin levels decline (6-9 months). Sickle cell trait (carrier): 8% of African Americans carry an HbS allele. Rarely causes sickling or anemia, except under severe conditions. Sickle cell trait confers resistance to malaria. Peripheral blood findings: RBC anisocytosis, poikilocytosis, sickled cells, reticulocytes; extramedullary hematopoiesis Complications of sickle cell disease: Chronic hemolytic anemia Painful crisis = vaso-occlusive crisis in bones (hand-foot syndrome or leg ulcers), lungs (acute chest syndrome), penis (priapism), brain (seizure or stroke), liver or spleen (infarct) Block: Foundations | REVELES [5 of 10] INTRODUCTION TO ANEMIAS Aplastic crisis = sudden stop of marrow RBC production (Parvovirus B19 infection) Sequestration crisis = sudden accumulation of RBCs in the spleen due to sludging Autosplenectomy: increase risk of infections (loss of splenic function; defective complement opsonization). RBC with Howell-Jolly bodies Microinfarcts expanding to gross infarcts, especially in solid organs (liver, brain, kidneys), but also in the lungs (cor pulmonale) Bone marrow expansion with thinning of cortical bone (“crew cut” or “hair- on-end” appearance of skull x-rays) Diagnosis: clinical findings, peripheral smear with sickle cells; hemoglobin electrophoresis; prenatal DNA testing for affected fetus Thalassemias Inherited disorder due to decrease of either alpha or beta globin chain synthesis. Two types, alpha and beta thalassemia depending on the affected gene o Alpha thalassemia: deletion of two or more alpha globin genes o Beta thalassemia: suboptimal or absent beta globin gene expression Laboratory findings: microcytic anemia with elevated red blood cell count and no significant anisocytosis. Target cells are characteristic. The degree of anemia and peripheral blood findings are mild in heterozygotes and more pronounced in homozygotes. Β thalassemia minor is associated with ⇧ HbA2 (>3.5%) Increased Rate of RBC Destruction (Hemolysis) Anemia can occur when RBC survival is shortened (normal ~120 days) due to abnormal RBC membrane structure, enzyme deficiency (G-6PD), immune- mediated, or mechanical red blood cell destruction. The immune-mediated hemolytic anemias will be covered in a lecture on Red Cell Immunology Immunity and Infection Block and the discussion here will focus on non-immune mediated hemolytic anemias. Common features of hemolytic anemias: Shortened RBC survival (due to premature RBC destruction) Elevated erythropoietin levels with compensatory increase in erythropoiesis ▪ Anemia with reticulocytosis Block: Foundations | REVELES [6 of 10] INTRODUCTION TO ANEMIAS Accumulation of hemoglobin breakdown products (hemosiderosis) Jaundice (increased serum bilirubin excreted into urine & feces, pigment gallstones) Low serum haptoglobin (scavenger protein clearing free hemoglobin from the circulation) Complications unique to patients with chronic hemolytic anemias: Aplastic crisis (often due to parvovirus B19 infection): lack of RBC production with continued accelerated destruction can lead to severe prolonged anemia Hemolytic crisis: super-accelerated destruction seen in response to systemic problems such as sepsis Hemolytic anemia due to mechanical trauma of RBC RBCs exposed to excessive physical stress can break apart. When this happens, they might completely disintegrate, or they might continue to circulate as fragments (“schistocytes”). Such damage (macroangiopathic hemolytic anemia) is most common with intravascular prostheses such as mechanical heart valves, ECMO, cardio-pulmonary bypass, ventricular assist devices, or vascular grafts (at the suture line). It is also typically seen in inflammatory conditions that allow fibrin to deposit within small vessels. The resulting partial occlusion by the fibrin strands pinches off pieces of the RBC membrane (microangiopathic hemolytic anemia). Examples include disseminated intravascular coagulation (DIC), systemic lupus erythematosus (SLE), and thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS). Clinical presentation: history as described above plus evidence of hemolysis Labs: Anemia with fragmented red cells (helmet cells, triangle cells, other non-specific schistocytes), thrombocytopenia, elevated LDH. Diagnosis: clinical history and presentation, negative antibody work-up (excludes immune mediated hemolysis), peripheral smear findings Anemia due to RBC membrane defects The unique features of RBCs and membrane skeletal proteins (ankyrin, band 3, protein 4.2, and spectrin) will be covered in detail by Dr. Marie-Pierre Hasne in a subsequent lecture in this block. Mutations in these proteins results in an abnormal, less deformable and rigid membrane with the consequence of shorter red cell life span due to premature removal by the spleen (hemolysis). Hereditary Spherocytosis (HS) Block: Foundations | REVELES [7 of 10] INTRODUCTION TO ANEMIAS The most common RBC membrane defect. As a result of microvesiculation and membrane loss, the RBCs appear spherical rather than biconcave. Genetics: Mutations in the ankyrin gene are most common; defects of band 3 and alpha spectrin are rare. Decreased flexibility makes it hard for the RBC to pass through small channels. Getting caught in splenic sinusoids leads to phagocytosis and destruction by splenic Characteristic triad: Anemia with marked reticulocytosis (bone marrow is trying to compensate for the anemia), jaundice (hemoglobin degradation products build up), and splenomegaly (reticuloendothelial system overload). The severity of anemia is variable from obvious hemolysis at birth to asymptomatic. Laboratory findings: Normochromic normocytic or microcytic anemia with circulating spherocytes and reticulocytosis Elevated MCHC >36 g/dL (characteristic finding) due to spherical shape of the RBCs Increased LDH Elevated indirect (unconjugated) bilirubin Reticulocytosis due to increased bone marrow and extramedullary erythropoiesis Diagnosis of HS: Presence of personal and family history of anemia along with elevated MCHC = presumptive diagnosis of HS Increase Osmotic fragility; Note, this test has low specificity and low sensitivity Flow cytometric detection of band 3 staining, EMA test, high specificity and sensitivity for HS Genetic testing is rarely necessary RBC enzyme defects, glucose-6-phosphate dehydrogenase (G6PD) deficiency. More details will be covered in the DMH block. G6PD deficiency is inherited as a X-linked autosomal recessive G6PD is a key enzyme in the glycolytic pathway that generates ATP and glutathione peroxidase necessary in protecting the RBC from generate free radicals. Self-limiting anemia: the new RBCs are released into the circulation with a “full load” of G6PD that is used in during the RBC lifespan Mature RBC cannot synthesize G6PD and deficiency will lead to hemolysis if the cells are exposed to oxidative stress such as chemicals (naphthalene, mothballs), medications (primaquine, dapsone), acute infections, and certain foods (fava beans) A majority of deficient individuals are asymptomatic and have no hemolysis at steady state. The following Anemias (iron deficiency/nutritional) are for your reference but will NOT be tested in this block: Block: Foundations | REVELES [8 of 10] INTRODUCTION TO ANEMIAS Iron Deficiency Anemia The most common nutritional deficiency worldwide (including the US). Causes of iron deficiency: Insufficient dietary intake (infants, vegetarians, elderly) Impaired absorption (intestinal disease, gastrectomy, diets rich in tannates, carbonates and phosphorous) Increased requirement during pregnancy and children during growth spurts Chronic blood loss (peptic ulcers, GI cancer, hematuria, menorrhagia, gynecologic cancers) Labs: ⇩⇩ hemoglobin (severe anemia), ⇩ reticulocyte count, ⇩ immature reticulocyte fraction ⇩ RET-He along with ⇩ serum iron; ⇩ transferrin saturation (