Approach to and Classification of Anemias Flashcards
define anemia
a decrease in RBC mass; characterized by:
- decreased RBC count
- decreased hemoglobin
- decreased HCT and PCV
describe the clinical consequences of anemia
- reduction in the oxygen carrying capacity of the blood (hypoxemia); can result in hypoxic tissue damage
- clinical signs due to decreased O2 delivery to tissues
-lethargy, exercise intolerance
-plus more clinical signs associated with the l=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 ID the underlying cause
describe the clinical diagnostic approach to anemia
- physical exam:
-pale MM
-weakness
-tachycardia
-pounding pulse
-heart murmur
-increased respiratory effort
-any other clues to cause or underlying disease - screen for blood loss with or without coagulopathy:
-melena, petechia or ecchymoses, epistaxis, hematoma formation, discolored urine (brown or red) - check for evidence of organomegaly:
-could indicate extramedullary hematopoiesis (esp spleen), tumor, hematoma - check for lymphadenopathy
- check for presence of ectoparasites
describe the laboratory diagnostic approach to anemia
minimum database! CBC, chem, UA
- CBC:
-document and assess anemia severity (RBC, HCT/PCV, Hb)
-assess if bone marrow is responding (degree of polychromasia, hemoparasites)
-eval RBC indices (MCH, MCHC)
-microscopic RBC morphology changes, RBC inclusions, hemoparasites
-ID plately or leukocyte changes - chemistry profile:
-bilirubin levels
-organ function and clues to underlying disease - urinalysis:
-more complete eval of renal system
-screen for hematuria, bilirubinuria, and hemoglobinuria
what are the goals of laboratory eval for anemia?
- determine severity
- determine is an appropriate bone marrow response is present
- determine general population
- determine specific pathophysiologic cause if possible
- determine additional tests:
-fecal (parasites), coomb’s (immune-mediated), coag panel, diagnostic imaging, PCR for infectious agents, bone marrow exam tissue biopsy/aspirates
describe classification of anemia (broadly)
- bone marrow response: regenerative vs nonregen
-regen: increased reticulocytes (if at least 3 days for bone marrow to be able to respond), mod to marked polychromasia, increased MCV, decreased MCHC and RDW (horses rarely release reticulocytes or polychromatophils so use serial CBC)
-nonregen: normocytic, normochromic, RDW normal, MCV and MCHC normal or decreased, decreased RBC production!
- RBC indices (MCV, MCHC, RDW)
- underlying mechanism
describe eval of bone marrow response to anemia
- regen versus non regen
-reticulocyte count used most often (not in horses)
-polychromasia on blood smear
-direct bone marrow exam (invasive)
-serial PCVs/HCT in horses!
if anemia is mild, don’t expect to see a robust increase in reticulocytes and/or polychromasia!
describe reticulocytes and polychromatophils
- if absolute reticulocyte count is > RI = regenerative anemia
-but production and release of reticulocytes takes 3-5 days! - mild polychromasia is normal in HEALTHY dogs
- slight polychromasia is often present in healthy cats
- any polychromasia/basophilic stippling in ruminants = regeneration (not much in health so any = significant)
- horses do NOT release reticulocytes; polychromasia is extremely rare even with severe anemia
relate nRBCs to anemia
- usually metarubricytes but can be earlier stages; rare is okay, but try to correct the WBC count is >5/100 WBCs (rubricytosis)
- appropriate rubricytosis: intensely regenerative anemia (HELLA increased reticulocytes, marked prolychromasia)
- inappropriate rubricytosis:
-nRBCs without reticulocytosis/polychromasia or disproportionate to the regenerative response
-related to spleen (dysfunction, disease, splenectomy), or bone marrow (neoplasia, damage)
describe anemia classification using RBC indices
- primarily based on MCV and MCHC but these are averages and therefore insensitive in detecting minor changes
MCV: can be microcytic, normocytic, or macrocytic
MCHC: can be hypochromic or normochromic
-hyperchromic does not occur, if present is a cue of free hemoglobin
describe normocytic (normal MCV) and normochromic (normal MCHC) anemia
- most common
- either non-regenerative anemia or early pre-regenerative anemia or regenerative but insufficient to shift the averages!
-take RDW, anisocytosis, polychromasia, and reticulocyte count into account before decide regen or not regen
describe microcytic (decreased MCV) hypochromic (decreased MCHC) anemia
- smaller and paler RBCs
- classic pattern of iron deficiency anemia
- can sometimes be seen in anemia of inflammatory disease
describe macrocytic (increased MCV), hypochromic (decreased MCHC) anemia
- markedly regenerative anemia
-reticulocytes are bigger with less hemoglobin than mature RBCs
-approx 10% of dogs with regen anemia have both and approx 30% have either or - lack of this pattern does NOT exclude regeneration
describe macrocytic alone (normochromic)
- regenerative anemia
- defective erythropoiesis (FeLV in cats)
- without anemia = congenital in poodles
describe hypochromasia alone (normocytic)
uncommon but seen in some regenerative anemias
describe microcytic alone (normochromic)
- early stages of iron deficiency
- portosystemic shunt
- without anemia = asian dog breeds (shiba inu, chow chow, akita, shar pei)
what are the 3 big categories of classification of anemia by underlying cause?
- blood/RBC loss/hemorrhage
-internal or external, typically regenerative anemias - increased RBC destruction/hemolysis
-intra or extravascular; typically regenerative - decreased RBC production
-nonregenerative; typically normocytic, normochromic anemia
-underlying bone marrow pathology, lack of stimuli (Epo), nutritional deficiencies (iron)
describe the 2 types of blood loss anemias
external blood loss:
-GI tract, repro tract, renal losses, blood-sucking ectoparasites
-total loss of protein and cells
-iron is also lost so if chronic, iron deficiency can develop
-regen anemia can become non-regen if not treated
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)
describe acute blood loss anemia
- the severity of lost RBCs will not be appreciated until the lost fluid volume is replaced (24-48hrs) when restored fluid volume dilutes RBCs and proteins
- it can take 3-5 days to mount a regenerative response so anemia will look non-regenerative initially (pre-regenerative)
- peak response is 4-7 days
describe chronic blood loss anemia
- small losses over a prolonged period of time; due to
-internal or external parasitism
-GI ulcers
-neoplasia resulting in blood loss (bleeding tumor)
-hematuria
-coagulopathis
-frequent blood draws (esp if tiny animal) - you may not detect anemia initially if production matches losses
- can develop into iron deficiency as iron stores are depleted
-initially regenerative but with time can progress to non-regen
describe RBC destruction in health
- in health animals approx 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 is physiologic
- hemolytic anemia results if RBCs are destroyed prematurely!! extra or intravascular
describe extravascular hemolysis
- when more unconjugated bilirubin is produced by macrophages than the liver can handle, unconjugated bilirubin builds up in blood, leading to high total bilirubin values
- also, conjugated bilirubin that builds up in the liver gets regurgitated back into the blood, leading to high conjugated bilirubin, which spills into the urine (bilirubinuria)
describe intravascular hemolysis
- 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); hemoglobin is toxic to kidneys so yikes
compare and contrast extravascular versus intravascular hemolysis
extravascular:
-RBCs are phagocytosed by macrophages (spleen, liver, bone marrow)
-most common!
intravascular:
-RBCs lyse in vasculature
-uncommon but more of a medical emergency
describe fragmentation anemia
- conditions causing increased RBC fragility, often seen with DIC
- usually only mild anemia or a contributor to anemia
