Rbcs - Intro

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Anemia

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- decreased red cell mass affecting tissue oxygenation
- Low Hb or low Hct
- sign of underlying disease

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Classification of anemia based on MCV

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microcytic
macrocytic
normocytic

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Classification of anemia based on etiology

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blood loss
impaired production
increased destruction

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increased blood loss causes

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acute: trauma
chronic: lesion of GI tract, gynecological disturbances

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clinical features of anemia

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fatigue, weakness, malaise
dyspnea w/ exertion
angina, cardiac failure (myocardial hypoxia)
anuria/oligouria (kidney hypoperfusion)
headache, inability to concentrate, dizziness

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signs of anemia

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pallor
compensatory mechanisms (increased RR, tachycardia, systolic murmur)

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steps of investigation

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CBC --> reticulocyte count --> erythrocyte sedimentation rate --> bone marrow exam

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What components are in a CBC?

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Hb
Hct or packed cell volume (PCV)
RBC count
RBC indices
RBC distribution width (RDW)
WBC count ( total leukocyte count, differential leukocyte count)
platelet count
evaluation of peripheral blood smear (PBS)

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most important index for classification of anemias

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MCV = Hb/ Hct
RBC count- average volume of RBCs

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Mean corpuscular hemoglobin concentration (MCHC)

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average Hb concerntration in a given volume of packed red cells
MCHV = Hb / PCV
expressed in g/dL

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Mean corpuscular hemoglobin
(MCH)

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average mass of Hb in an individual RBC
MCH = Hb/RBC count

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TLC and platelet count are done to

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rule out pancytopenia

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anisocytosis

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seen on PBS
variation in size
non-specific finding

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Poikilocytosis

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seen on PBS
variation in shape
non-specific finding

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hypochromasia

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increased central pallor
due to decreased Hb

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polychomasia

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result of premature RBCs
RBCs of more than one color
larger bluish gray
reticulocytes

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normoblastemia

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presence of nucleated RBCs in the PBS
seen in hemolytic anemias

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Spherocytes

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have no central pallor
seen in hereditary spherocytosis and auto-immune hemolytic anemias

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Schistocytes

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fragments of RBCs
seen in micro-angiopathic hemolytic anemia (DIC,TTP, HUS)
other hemolytic anemias

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punctate basophilia/ basophilic stippling

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ribosomal fragments surrounding the nucleus
caused by sever anemia, lead poisioning*, severe infection, drug exposure, and alcoholism

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Howell-jolly bodies

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purple nuclear remnants
larger than basophilic stippling
indicate absence of spleen or hemolysis

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RDW (RBC distribution width)

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degree of variation in RBC size
increased if RBCs are not uniformly the same size (mixture of microcytic and normocytic cells)
Iron deficiency anemia is the only microcytic anemia w/ increased RDW due to a mixture of normocytic and microcytic RBCs

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Reticulocytes

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newly released RBCs from bone marrow
identified w/ supravital stains
detect thread like RNA filaments in cytoplasm
become mature RBCs in 24 hours

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Erythropoiesis

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production of RBCs in bone marrow
depends on the release of erythoropoietin from the kidneys

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Reticulocyte count

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marker of effective erythropoiesis (the bone marrows response to anemia)
normal is <3%
% count is falsely increased in anemia therefore it must be corrected with (patients Hct/45) x reticulocyte count = corrected count

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Microcytic anemia

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MCV < 80fL
causes: iron deficiency anemia (most common), anemia of chronic disease, thalassemia, sideroblastic anemia (least common)

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Lab tests in microcytic anemias

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serum iron
serum total iron binding capacity
% saturation
serum ferritin (calc. fraction of storage iron)
Hb electrophoresis

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Macrocytic anemia

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MCV > 100 fL
Common causes: vit B12/folate deficiency, alcohol use, liver disease, reticulocytosis
uncommon causes: myelodysplastic syndrome, hypothroidism

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Normocytic anemia

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MCV 80-100fL
Reticulocyte count (<3%): acute blood loss (<7 days), aplastic anemia, anemia of chronic disease, renal disease, early iron deficiency
reticulocyte count (>3%): intrinsic RBC defect (membrane defects, abnormal Hb, defective enzyme) extrinsic RBC defect (auto immune hemolytic anemia, PNH, micro-angiopathic hemolytic anemia)

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Anemia due to acute blood loss if patient survives

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intravascular shift of water from interstitial fluid compartment
hemodilution - low PCV
reduced oxygen - EPO stimulated erythroid hyperplasia
reticulocytes appear in peripheral blood after 5 days

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anemia due to acute blood loss if massive blood loss

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cardiovascular collapse, shock, and death

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causes of acute blood loss

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external blood loss (peptic ulcer) may result in iron deficiency
internal blood loss (ruptured abdominal aortic aneurysm) iron is recaptured

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clincal effects of acute blood loss depend on

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rate of hemorrhage
whether bleeding is external or internal

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Lab findings in acute blood loss

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Hb - low
PCV - low (may take 24-48 hours)
TLC - increased (earliest change) mobilization of granulocytes from marginal pools
PBS - normocytic normochromic initially, polychromasia > 5-7 days
Reticulocyte count - increase (10-15%) after 5-7 days
Platelets - increased platelet production