6 – RBC 4

Question 1

What is erythrocytosis?

Answer 1

• Increased [RBC] in peripheral blood

Question 2

How is erythrocytosis detected?

Answer 2

• Increased RBC count
• Increased Hgb concentration
• And/or increased hematocrit (Hct) on CBC
  o Some have a high Hct normally (hounds)

Question 3

What is polycythemia?

Answer 3

• Increased RBC, WBC and platelets
• *neoplasic process

Question 4

What are the 2 types of erythrocytosis?

Answer 4

1. Relative
2. Absolute
   *cannot tell by looking at CBC alone (ex. may use imaging)

Question 5

What can cause relative erythrocytosis?

Answer 5

• Dehydration
• Splenic contraction
• *NO new erythrocytes made

Question 6

Dehydration: relative erythrocytosis

Answer 6

• Other evidence of dehydration (ex. increased proteins)
• Re-evaluate once adequately hydrated

Question 7

Splenic contraction: relative erythrocytosis

Answer 7

• Excited animal (ex. especially horses and cats)
  o Proteins WRI
• Re-evaluate when calmed

Question 8

Absolute erythrocytosis

Answer 8

• Increase in total RBC
• Mild to marked
• *primary or secondary

Question 9

Where is erythropoietin (EPO) produced?

Answer 9

• Adult kidney: Renal peritubular interstitial cells produce it in response to renal HYPOXIA
  o EPO produced within mins to hours
  o Maximum production reached at 24hr
  o New RBC in circulation 2-4 days later
• **negative feedback loop

Question 10

What can cause primary absolute erythrocytosis?

Answer 10

• Neoplasia
• *NO increase in EPO

Question 11

Neoplasia: primary absolute erythrocytosis

Answer 11

• Neoplasia of hematopoietic cells
  o Uncontrolled proliferation
• EPO level low or WRI
• Arterial pO2 WRI
  o May be decreased with marked erythrocytosis
  o Due to increased blood viscosity from all the RBCs

Question 12

What can cause secondary absolute erythrocytosis?

Answer 12

• Appropriate (physiologic)
• Inappropriate (pathologic)

Question 13

Appropriate (physiologic) secondary absolute erythrocytosis

Answer 13

• Increased EPO in response to poor tissue oxygenation
  o Cardiac or pulmonary disease
  o Hyperthyroidism
  o Move to higher altitude
• Arterial pO2 increased initially
  o May result in compensation

Question 14

Inappropriate (pathologic) secondary absolute erythrocytosis

Answer 14

• Increased EPO due to disease
  o Renal tumors, cysts, hydronephrosis
  o Tumors of liver or smooth muscle
• Arterial pO2 WRI