Lecture 8 - HAEM 5

Question 1

Where is thrombopoietin (TPO) made?

Answer 1

Produced by various cells in the body - mainly by renal tubular epithelial, bone marrow stromal cells, hepatocytes

Question 2

How does IL-6 stimulate thrombopoiesis?

Answer 2

IL-6 increases production of TPO by the liver –> thrombocytosis

Question 3

Briefly explain how TPO can regulate thrombopoiesis?

Answer 3

TPO receptors on blood platelets and maturing magakaryocytes can bind internalise and degrade TPO providing negative feedback on platelet production

Question 4

Briefly describe the kinetics of platelets:

Answer 4

Approximately 30% of circulating mass is transiently compartmentalised in spleen. Platelets circulate for approximately 5-9 days in most mammalian species

Question 5

What are the two main reasons that there is frequently errors in feline blood platelet counts?

Answer 5

In standard collecting tubes - containing EDTA as an anticoagulant there is frequent (up to 71%) platelet aggregation

Another common error with feline platelet counts (PLT) is that many feline platelets are too big are not counted as platelets

Question 6

Briefly explain how platelet counts work:

Answer 6

Volume detection is measured by changes in conductance.

The number of impulses = concentration of particles

Amplitude of impulsion = size of particles = types of cell

Question 7

How many platelets should be seen per hpf (x100) under normal physiological conditions?

Answer 7

Dogs, cat, cattle = 8-10 plt/hpf

Horses = 5 plt/hpf

Question 8

What is thrombocytopenia and what are the common clinical signs that accompany it?

Answer 8

A decrease in circulating platelets (most common acquired haemostatic disorder)

Clinical signs: petechiation or ecchymosis in tissues or mucosal membranes

Question 9

What are the main causes of thrombocytopenia?

Answer 9

Decreased or defective platelet production - acquired megakaryocytic hypoplasia or aplasia

Increased platelet loss - massive trauma and extensive external haemorrhage

Accelerated consumption of platelets - DIC

Increased platelet destruction - primary (idiopathic), secondary - infectious agents, neoplasia, drugs, immune mediated

Abnormal platelet distribution

Question 10

How frequent is selective megakaryocyte hypoplasia?

Answer 10

Rare - usually associated with defects of other lineages (Bi or pan-cytopenia)

Question 11

What blood results would be seen with increased platelet loss as a result of increased platelet loss due to massive trauma or extensive external haemorrhage?

Answer 11

usually mild to moderate, transient and reversible thrombocytopenia

Question 12

What blood results would be seen as a result of accelerated consumption of platelets and thrombotic microangiopathies?

Answer 12

Thrombocytopenia, haemolytic anaemia, and thrombosis

Question 13

In what circumstances do patients with primary (idiopathic) IMT normally present and how is it diagnosed?

Answer 13

Haemorrhage involving skin and mucosal surfaced - may arise spontaneously or due to pathologic prolonged bleeding following oestrus, whelping, surgery, dentistry, grooming on venipuncture

Question 14

In normal healthy animals what proportion of the platelet mass is stored in the spleen?

Answer 14

30% of platelet mass

Question 15

What occurs in redistribution thrombocytopenia?

Answer 15

Where platelets become reversibly sequestered in tissues.

Mild to moderate thrombocytopenia may result from sequestration in animals with any condition associated with splenomegaly or hepatomegaly

Question 16

What are the four main reasons that thrombocytosis may result?

Answer 16

1. Physiologic - splenic contraction and epinephrine
2. Drug induced - epinephrine and vincristine
3. Reactive - inflammation, infection, neoplasia, trauma, rebound from thrombocytopenia
4. Essential thrombocytopenia

Question 17

Briefly explain how physiologic thrombocytosis may occur:

Answer 17

Up to one-third of platelets is normally sequestered in splenic red pulp - these stores can be released upon splenic contraction (a process that is mediated by epinephrine)

Question 18

Briefly explain how vincristine and epinephrine induce thrombocytosis?

Answer 18

Vincristine - enhanced megakaryopoiesis

Epinephrine - induces a rapid, transient , thrombocytosis in dogs through splenic contraction

Question 19

Briefly explain the cause of reactive thrombocytosis and the provide examples of conditions that could cause it:

Answer 19

Due to cytokine stimulation (mainly IL-6) of thrombopoiesis. Occurs secondarily to inflammation, infection, neoplasia, trauma, rebound from thrombocytopenia, iron deficiency related

Question 20

What is the function of Von-Willebrand factor?

Answer 20

vWF = bridge between platelets and sub-endothelial matrix - binds platelets and collagen

Question 21

What are the three different types of vWD?

Answer 21

Type 1 = equal decrease in all sizes of multimeters = quantitate change
Type 2 = decrease in only the large multimeters = qualitative change
Type 3 = no detectable vWF factor

Question 22

What is Glanzmann thromboasthenia and what are the three main types of it?

Answer 22

Type 1: less than 5% of the receptor is detectable on platelet surface = clot retraction is invisible 
Type 2: 10-20%. of the receptor is present on platelet surfaces = clot retraction is detectable but reduced 
Variant: receptor is present but dysfunctional = clot retraction may or may not be detectable