VETM 5291 Anemia Lectures (Meichner) eLC PDF

VETM 5291 Year 2: Spring 2025 Approach to and classification of anemias Kristina Meichner DVM, DECVIM-CA (oncology), DACVP (clinical pathology) [email protected] January 3, 2025  Self study questions: CRHL year 1 and...

VETM 5291 Year 2: Spring 2025 Approach to and classification of anemias Kristina Meichner DVM, DECVIM-CA (oncology), DACVP (clinical pathology) [email protected] January 3, 2025  Self study questions: CRHL year 1 and F2a Where are red blood cells (RBCs) produced? What stimulates RBC production? What is the primary function of RBCs? A decrease in red blood cell mass is referred to as _______________ An increase in red blood cell mass is referred to as _______________ What RBC parameters are usually reported on a CBC? What are MCV, MCHC and RDW? What are reticulocytes? How can they be used to classify anemia? Discuss species differences. What is the difference between mammalian RBCs and RBCs from birds, reptiles and amphibians?  Learning objectives Recognize anemia and classify based on bone marrow response and underlying mechanism Discuss the pathogenesis and pathophysiology of blood loss anemia and hemolytic anemia and explain how to distinguish them clinically and on a CBC Identify non-regenerative anemia using all available data: construct a species-appropriate list of differentials and discuss the pathogenesis and typical clinical pathology findings  Lecture overview Anemia  Definition  Clinical signs  Laboratory evaluation  Classification based on Red blood cell indices (MCV, MCHC) Bone marrow response (reticulocytes) Mechanism (RBC loss, destruction/hemolysis, …) Types of anemias  Regenerative anemia Blood loss anemia Hemolytic anemia  Non-regenerative anemia  Anemia: definition Anemia is a decrease in RBC mass and characterized by  ↓ RBC count  ↓ hemoglobin  ↓ HCT and PCV PCV within reference interval Decreased PCV (image from eClinPath)  Additional microscopic findings Erythrogram  Anemia: clinical consequences Reduction in the oxygen carrying capacity of the blood (hypoxemia)  Can result in hypoxic tissue damage Clinical signs due to ↓O2 delivery to tissues  Lethargy, exercise intolerance  + clinical signs depending on the underlying mechanism Clinical manifestations depend on  Severity, rate of onset, physical activity and underlying cause (!) Anemia is a clinical syndrome, not a disease or diagnosis! – you must identify the underlying cause!  Anemia – clinical diagnostic approach Physical exam  Pale MM, weakness, tachycardia, pounding pulse, heart murmur, increased respiratory effort  Clues to the cause of the anemia or underlying disease? Blood loss with or without coagulopathy  Melena  Petechia or ecchymoses  Epistaxis  Hematoma formation  Discolored urine (brown, red) Organomegaly  EMH (extramedullary hematopoiesis, esp. spleen), tumor, hematoma Lymphadenopathy Presence of ectoparasites  Anemia – laboratory diagnostic approach Minimum database (MDB) CBC  Document and assess anemia severity (RBC, HCT/PCV, Hb)  Assess if bone marrow is responding (degree of polychromasia, reticulocytes)  Evaluate RBC indices (MCV, MCHC)  Microscopic RBC morphology changes, RBC inclusions, hemoparasites  Identify platelet or leukocyte changes Chemistry profile  Bilirubin levels  Organ function and clues to underlying disease Urinalysis  More complete evaluation of the renal system  Screen for hematuria, bilirubinuria and hemoglobinuria  Goals of Laboratory Evaluation Determine severity Determine if an appropriate bone marrow response is present Determine general mechanism Determine specific pathophysiologic cause if possible Determine additional tests (see next slide)  Anemia – diagnostic approach Additional test, based on history, PE findings, and MDB, can include  Fecal exam for parasites  Coombs’ testing (immune-mediated causes)  Coagulation panel (bleeding disorder)  Diagnostic imaging (radiographs, ultrasound, ….)  PCR for infectious agents (i.e., hemoparasites)  Bone marrow examination (i.e., severe non-regenerative anemia without obvious underlying mechanism, pancytopenia)  Tissue biopsy/aspirates (look for neoplasia, infection, inflammation)  Anemia – classification 1. Bone marrow response (regenerative vs non-regenerative) 2. RBC indices (MCV, MCHC, RDW) 3. Underlying mechanism You will use aspects of all three to construct a differential list  Anemia classification: big picture Regenerative anemia Non-regenerative anemia Reticulocytes * ↑ N or ↓/absent Polychromasia * Moderate to marked Mild to absent MCV, MCHC, RDW * MCV ↑, MCHC ↓, RDW ↑ MCV N or ↓, MCHC N or ↓, RDW N Blood loss # Yes ^ Hemolysis Yes! ^ Decreased RBC production No Yes! * take species differences into account # After acute blood loss, severity of anemia may not be immediately apparent. Chronic bleeding can cause iron deficiency over time, an a regenerative anemia can transition to non-regenerative anemia. ^ Note: regeneration may not be apparent within the first 3 days of acute blood loss and/or hemolysis. Review the Foundation 2a RBC lecture 1 and 2 for more details on RBC parameters, RBC indices (MCV, MCHC, RDW), reticulocytes, nRBCs and RBC morphology changes! Classification by bone marrow response Regenerative vs. non-regenerative anemia  Bone marrow response to anemia Regenerative vs. non-regenerative anemia  Reticulocyte count ** (used most often)  Polychromasia on a blood smear  Direct examination of bone marrow  Serial PCVs/HCTs  which species? Note: if anemia is mild, don’t expect to see a robust increase in reticulocytes and/or polychromasia. Reticulocytes (polychromatophils) Polychromasia (Wright-Giemsa) Reticulocyte (NMB)  Reticulocytes and polychromatophils Absolute reticulocyte count > RI: regenerative anemia Production and release of reticulocytes takes 3-5 days Mild polychromasia is normal in healthy dogs Slight polychromasia often present in healthy cats Any polychromasia in ruminants = regeneration Horses – don’t release reticulocytes. Polychromasia is extremely rare, even with severe anemia What about nRBCs? Usually metarubricytes, can be earlier stages Rare is OK, but correct WBC count if > 5/100 WBCs (rubricytosis)  Automated analyzers count them as WBC because of the nucleus! Appropriate rubricytosis  Intensely regenerative anemias (↑↑ reticulocytes, marked polychromasia) Inappropriate rubricytosis  nRBCs without reticulocytosis/polychromasia or disproportionate to the regenerative response  Related with which organ(s)?? Spleen (dysfunction; disease; splenectomy) Bone marrow (neoplasia; damage (trauma, hypoxia, heat stroke), lead,…) Anemia classification using RBC indices  Classification of anemia: RBC indices Primarily based on MCV and MCHC  These are averages and therefore insensitive in detecting minor changes MCV MCHC Microcytic Hypochromic Normocytic Normochromic Macrocytic * *Hyperchromic cells do not occur  Classification of anemia: RBC indices Normocytic (normal MCV), normochromic (normal MCHC) anemia  Most common  Non-regenerative anemia  Pre-regenerative anemia (early)  Regenerative but insufficient to shift the averages! Also take RDW, anisocytosis, polychromasia and reticulocyte count into account before deciding if regenerative or non-regenerative  Classification of anemia: RBC indices Microcytic (↓ MCV), hypochromic (↓ MCHC) anemia  Smaller and paler RBCs  Classic pattern of iron deficiency anemia! ( more later)  Can sometimes be seen in anemia of inflammatory disease  Classification of anemia: RBC indices Macrocytic (↑ MCV), hypochromic (↓ MCHC) anemia  Markedly regenerative anemia Remember: reticulocytes are larger cells with less hemoglobin Approximately 10% of dogs with regenerative anemia have this pattern Approximately 30% of dogs with regenerative anemia have either/or  Lack of this pattern does not exclude regeneration! Classification of anemia: RBC indices, summary Macrocytic, hypochromic anemia  Strongly regenerative anemia Normocytic, normochromic  Implies non-regenerative but look at RDW, anisocytosis, polychromasia, retics Microcytic, hypochromic  Iron deficiency anemia Classification of anemia: RBC indices, summary Macrocytic alone (normochromic)  Regenerative anemia  Defective erythropoiesis (FeLV in cats)  w/o anemia – congenital in poodles Hypochromasia alone (normocytic)  Uncommon, some regenerative anemias Microcytic alone (normochromic)  Iron deficiency (microcytosis comes first)  Portosystemic shunt  w/o anemia – Asian dog breeds (Shiba Inu, Chow Chow, Akita, Shar Pei) Classification by general mechanism RBC loss RBC destruction (hemolysis) Decreased RBC production  Anemia – classification 1. Bone marrow response  Regenerative vs. non-regenerative (reticulocyte count) 2. RBC indices (MCV, MCHC, RDW) 3. Underlying mechanism – 3 big categories  Blood (RBC) loss  Increased RBC destruction (hemolysis)  Decreased RBC production Classification of anemia by mechanism Hemorrhage (Blood loss)  Internal or external  Regenerative Hemolysis  Intra- or extravascular  Regenerative Decreased production  Non-regenerative; typically, normocytic, normochromic anemia  Underlying bone marrow pathology  Lack of stimuli (i.e., Epo)  Nutritional deficiencies (i.e., iron) Anemia classification and mechanisms Blood loss Regenerative ↑ retics, polychromasia Anemia Hemolysis ↓ RBC, HCT, Hb Decreased RBC Non-regenerative production  Regenerative anemias – blood loss External blood loss  GI tract, reproductive tract, renal losses, blood-sucking ectoparasites  Total loss of protein and cells  Iron is also lost  with chronicity, iron deficiency can develop Regenerative anemia can get non-regenerative if left untreated! Internal blood loss  Hemorrhage into tissues, peritoneal or pleural cavity Erythrocytes and proteins are broken down Iron is available to reuse Into cavities: 2/3 of lost RBCs are absorbed within the first 2 days (autotransfusion)  Regenerative anemias – blood loss Acute blood loss  The severity of lost RBCs will not be appreciated until the lost fluid volume is replaced (24-48 hrs)  restored fluid volume dilutes RBCs and proteins  It can 3-5 days to mount a regenerative response  anemia will look non- regenerative initially (pre-regenerative)  Peak response: 4-7 days  Regenerative anemias – blood loss Chronic blood loss: small losses over a prolonged period of time  Internal or external parasitism  GI ulcers  Neoplasia resulting in blood loss (i.e., bleeding tumor)  Hematuria  Coagulopathies  Frequent blood draws You may not detect anemia initially  production matches losses Can develop into iron deficiency as iron stores are depleted  Initially regenerative, with time poorly to non-regenerative anemia! Anemia classification and mechanisms Blood loss Regenerative ↑ retics, polychromasia Anemia Hemolysis ↓ RBC, HCT, Hb Decreased RBC Non-regenerative production  RBC destruction in health In healthy animals, ~ 1% of RBCs are removed from circulation each day due to normal aging and damage once they have completed their lifespan RBCs are degraded within macrophages  Iron is recycled  Hemoglobin is released and metabolized to bilirubin This is a form of extravascular hemolysis, but it is physiologic Hemolytic anemia results if RBCs are destroyed prematurely!  Extravascular  Intravascular RBC destruction in health Phagocytized RBCs are broken down and the heme group in hemoglobin converted to unconjugated bilirubin. This is then exported from the macrophage, binds to albumin and is taken up by hepatocytes. Once in the hepatocyte, the bilirubin is conjugated and excreted into bile. Image from eclinpath.com  Premature RBC destruction leading to hemolytic anemia EV hemolysis:  When more unconjugated bilirubin is produced by the macrophages than the liver can handle, unconjugated bilirubin builds up in blood, leading to high total bilirubin values.  In addition, conjugated bilirubin that builds up in the liver gets “regurgitated” back into blood, leading to high conjugated bilirubin, which spills into the urine (bilirubinuria) IV hemolysis bilirubinuria  Free hemoglobin from IV hemolysis is liberated into the circulation (hemoglobinemia). Some of it is taken up by macrophages and hepatocytes, and bilirubin is formed.  Most of the free hemoglobin is filtered through the kidneys and excreted in the urine (hemoglobinuria). Image from eclinpath.com  Regenerative anemias Blood loss Hemolysis Bone marrow response Plasma or serum protein Hemoglobinemia Hemoglobinuria RBC morphology Hyperbilirubinemia Bilirubinuria Coombs’ test  Regenerative anemias – hemolysis Hemolysis = destruction of RBCs Extravascular hemolysis  RBCs are phagocytosed by macrophages (spleen, liver, bone marrow)  Most common! Intravascular hemolysis  RBCs lyse in the vasculature  Uncommon Fragmentation anemia  Conditions causing increased RBC fragility, often seen with DIC  Usually only mild anemia or a contributor to anemia  Extra- vs. intravascular hemolysis Extravascular Intravascular Onset Hemoglobinemia Hemoglobinuria RBC morphology Hyperbilirubinemia Bilirubinuria MCHC Reticulocytosis  VETM 5191 Year 2: Spring 2025 Hemolytic anemias Non-regenerative anemias Kristina Meichner DVM, DECVIM-CA (oncology), DACVP (clinical pathology) [email protected] January 2025  Overview Hemolytic anemias  Immune-mediated hemolytic anemia (IMHA)  Oxidative damage causing hemolysis  Infectious causes of hemolysis  Fragmentation of RBCs  “Lela” 3 year old F/S Cocker Spaniel 2 day history of lethargy, anorexia, and restlessness PE: weak, febrile (104.4°F), tachycardic, panting, icteric, pale mucous membranes Test code Results Expected Units RBC 4.01 L 4.98 – 7.92 X 106/μL HGB 9.0 L 12.6 – 19.9 g/dL HCT 27.6 L 36.6 – 59.6 % MCV 73 H 60 – 72 fL MCHC 32.5 L 34 – 36 g/dL RDW 23.9 H 11.3 – 13.5 % PLT 245 200 – 500 X 103/μL Reticulocytes 284,000 H 0 – 91,000 /μL nRBC 6H