RBC 4: Erythrocytosis

Question 1

What is erythrocytosis?

Answer 1

Increased RBC concentration in peripheral blood
-see increased RBC count
-increased hemoglobin concentration
-increased hematocrit on CBC

Question 2

What animals have normal high hematocrit?

Answer 2

-Sight hound dogs

-Hot blooded horses

***not erythrocytosis

Question 3

What is polycythemia?

Answer 3

Increased RBC, WBC, and platelets
-neoplasia process

Question 4

Two types of erythrocytosis?

Answer 4

1. Relative (dehydration and splenic contraction)
   2.Absolute (primary and secondary)

Question 5

Relative erythrocytosis

Answer 5

-most common
-mild to moderate
-main cause is dehydration, next is splenic contraction
-no new red cells are being made

Question 6

Dehydration Relative erythrocytosis

Answer 6

-will see other evidence of dehydration eg. increased proteins
-need to re-evaluate once adequately hydrated

Question 7

Splenic contraction Relative erythrocytosis

Answer 7

-occurs in excited animals (horses and cats)
-results in red cells being pushed into circulation from the spleen
-proteins will be in normal range
-need to re-evaluate when calm

Question 8

Absolute erythrocytosis

Answer 8

-An increase in the total RBC mass
-from mild to marked
-can be primary or secondary

Question 9

Where does Erythropoietin production occur?

Answer 9

Produced in adult kidney by the renal peritubular interstitial cells in response to renal hypoxia (indicator of total body hypoxia)
*negative feedback loop will turn off when new RBC levels return to normal

Question 10

Timing of erythropoietin production

Answer 10

-Produced within mins to hours
-max production reached at 24hrs
-new RBC in circulation 2-4 days later

Question 11

Primary absolute erythrocytosis

Answer 11

Neoplasia of hematopoietic cells results in uncontrolled proliferation

-erythropoietin levels are low or within reference levels
-arterial pO2 within reference intervals… but may decrease in marked cases because increased RBCs increase the blood viscosity so oxygenation may be impaired

Question 12

Secondary Absolute erythrocytosis

Answer 12

Occurs secondary to increase erythropoietin

Types:
1. Appropriate (physiologic)
2. Inappropriate (pathologic)

Question 13

When does Appropriate secondary Absolute erythrocytosis occur?

Answer 13

Increased erythropoietin in response to poor tissue oxygenation
Eg. cardiac or pulmonary disease, hyperthyroidism, move to high altitude

Note: arterial pO2 decreased initially but over time may result in compensation to a normal pO2

Question 14

When does Inappropriate secondary Absolute erythrocytosis occur?

Answer 14

Will see increased erythropoietin due to disease. Negative feedback loop after increased RBC production in bone marrow is not occurring
eg. renal tumours, cysts, hydronephrosis, liver tumours, smooth muscle tumours

Note: Arterial pO2 in normal reference intervals

Question 15

Erythrocytosis checklist

Answer 15

Question 16

Hematocrit and total protein changes and the likely causes

Answer 16