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

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