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Clinical Pathology - RBC Morphology

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What are the functions of RBCs?
to carry oxygen bound to hemoglobin to tissues and carry CO2 to lungs for excretion
What do RBCs convert CO2 into?
bicarbonate
Where are RBCs produced?
in the bone marrow
What is hematopoiesis?
production of blood cells
What is erythropoiesis?
production of RBCs
What is extramedullary hematopoiesis?
hematopoiesis that takes place outside the bone marrow (often in spleen or liver)
Extramedullary hematopoiesis can be in response to what?
severe anemia or other pathological condition such as neoplasia
What can a pluripotent stem cell become?
depending on various cytokines and hormones, they can become RBCs, granulocytes, platelets or lymphocytes
What is the main factor in production of RBCs?
erythropoietin
What is erythropoietin produced by?
the fetal liver and adult kidney
Renal peritubular cells produce erythropoietin in response to what?
renal hypoxia
What is the shape of RBCs in:
- most mammals?
- camelids?
- birds, reptiles, amphibians and fish?
mammals - biconcave disc
camelids - ovoid
birds, reptiles, amphibians and fish - nucleated ovoid
Which RBCs have a higher Hb concentration?
camelids
What does a biconcave disc shaped RBC allow for?
bending of RBC when passing through capillaries
What is hemoglobin?
the major molecule in RBCs that carries oxygen bound to iron
Where is hemoglobin produced?
in the bone marrow while RBC is nucleated and for short time after release as a reticulocyte
Where is most of the iron in the body present?
in Hb in RBCs
Some iron is present bound to transport proteins in the blood such as what?
transferrin
When iron is stored in the liver, bone marrow and spleen what is it known as?
ferritin
Iron can only be lost by how?
hemorrhage
What is the main pathway for RBC destruction?
extravascular destruction; hemoglobin is split into heme and globin; globin is broken down in AAs for recycling; iron is split from heme molecule; heme is broken down by heme oxygenase to CO and biliverdin; biliverdin is reduced to bilirubin; bilirubin is bound to albumin for transport to the liver; bilirubin is conjugated to glucuronic acid and excreted into the bile; small amounts of unconjugated bilirubin can be excreted by the kidney
Why do bruises turn to yellow?
because of the bilirubin due to hemoglobin breakdown
Which animal lacks biliverdin reductase?
birds (this is why they develop green discoloration as hemoglobin is broken down in bruises)
What is the minor pathway for RBC destruction?
intravascular lysis of aged RBCs; plasma protein haptoglobin binds hemoglobin for transport to the liver and hemoglobin's fate is the same as for extravascular destruction
Abnormalities in size of RBCs:
-anisocytosis?
-macrocytosis?
-microcytosis?
anisocytosis: variation in sizes
macrocytosis: larger than normal
microcytosis: smaller than normal
Abnormalities in color of RBCs:
-polychromasia?
-hypochromasia?
polychromasia - bluish discoloration to RBC
hypochromasia - decreased hemoglobin content
Abnormalities in shape of RBCs:
-poikilocytosis?
-spherocytosis?
poikilocytosis - abnormal shapes
spherocytosis - small dense RBCs
Abnormalities in distribution of RBCs:
-rouleaux?
-agglutination?
rouleaux - stacking of RBCs
agglutination - RBCs sticking to each other
What are the five abnormalities that can occur in RBCs?
abnormalities in size, color, shape and distribution and inclusion bodies/infectious agents
What is the marker of immune-mediated hemolytic anemia?
spherocytosis
What is crenation?
numerous pin-point projections
What are acanthocytes?
where there are a few irregular elongations of RBC border with rounded ends often forming a bud
What are acanthocytes often seen with?
hemangiosarcoma, hepatic disease and renal disease
What are schistocytes?
erythrocyte fragmentations
Schistocytes can be a sign of what?
hemangiosarcoma or DIC
Target cells, or codocytes, are seen in what disorders?
anemia or liver/renal/lipid disorders
Rouleaux formation is a normal finding in what species?
horses and sometimes cats
Rouleaux formation indicates what in small animals?
inflammation
What can agglutination suggest?
hemolytic anemia
How can you differentiate rouleaux from agglutination?
mix blood with normal saline - rouleaux will dissipate and agglutination will not
What are Howell Jolly bodies?
nuclear remnants in RBC
What percent in feline blood are Howell Jolly bodies normal?
up to 1%
Howell Jolly bodies are signs of what?
regeneration in anemia
What are Heinz bodies?
denatured hemoglobin - does not stain well with regular stain
Heinz bodies can be seen in up to what percent of normal cats?
10%
What are reticulocytes?
young (immature) erythrocytes prematurely released to the blood from the bone marrow in some anemias
What are the clinical applications of reticulocytes?
evaluation of erythropoiesis in bone marrow and differentiation of regenerative and non-regenerative anemia
What is indicated if absolute reticulocyte count is higher than 60,000/uL?
a sign of regeneration
How do you calculate corrected reticulocyte percentage (CRP)?
CRP = % reticulocytes x PCV of a sample/normal PCV
How do you calculate reticulocyte production index (RPI)?
RPI = CRP/maturation index (MI)
How do you interpret RPI?
RPI > 3: very good regeneration
RPI = 1-3: good regeneration
RPI < 1: inadequate regeneration
What are the two types of reticulocytes that cats have?
aggregate (blue stained coarse clumping) and punctate (small, blue stained dots)
In cats, what do aggregated reticulocytes indicate?
recent response
In cats, what do punctate reticulocytes indicate?
response to anemia occurring 3-4 weeks previously