Four main functions of platelets?

1. Maintain vascular integrity by sealing endothelial defects
2. Helping to stop bleeding- form platelet plug
3. Contribute to membrane lipid procoagulant activity- secondary hemostasis (coagulation)
4. Promote vascular healing through the release of platelet derived growth factors (PDGF)

Platelets are produced in the bone marrow from a precursor cell called a?

This occurs in a process called?

Megakaryocyte

Cytoplasmic Demarcation

Circulating thrombopoietin levels apper to be inversely correlated with platelet levels

True/False?

2/3 to 3/4

There is free exchange between the splenic and circulating pools

3 to 7

Old platelets are remeoved from the body through phagocytosis by macrophages

Automated platelet counts are reliable for dogs but not for most other domestic specis.

True/False?

True

Platelets from other specis are prone to clump, which would alter the automated platelet counter

When mild to moderate thrombocytopenia is noted in a dog, it should be flaged as suspect and recounted

BMBT stands for what?

What is it used for?

It is only a value when platelet counts are above what level per ul?

Buccal Mucosal Bleeding Time

Test to determine adequacy of endothelial cell and platelet function.  More sensitive for platelet function.

75,000/ ul

What is the process for performing the BMBT test?

What is the reference range for a dogs and cat for BMBT time?

A "bleeding time device" that creates a standardized incision is utilized.  The test is performed on the patients upper lip buccal mucosa.  The patient is non-anesthetized.  Blood seeps from the incision, and a paper towel is used to soak it up without blocking the incision.  The time from incision to cessation is the BMBT.

1.8 to 4.2 minutes

MPV is usually proportional to the platlet number?

True/False?

Dog:  6 to 10 femtoliters

Cat:  12 to 18 femtoliters

Elevation in MPV is suggestive of active (responsive) platelet production.  Artifactual increases occure with EDTA, when platelets are refrigerated, or if there is delayed exposure to anticoagulant. 

MPV is best measured from blood collected into what, and stored at what temperature?

PDW stands for what?

Platelet Distrubution Width

An index of variation in platelet size, used to determine the presence of abnormally sized platelets

Petechiae- capillary or postcapillary venule hemorrhage

Coalescing petechiae are called purpura

1. Sequestration
2. Hypoproliferation
3. Consumption
4. Destruction

1. Very low peripheral platelet counts (<50,000/ul)
2. Bone marrows are nearly devoid of megakaryocytes

1. Infections- Ehrlichia, FIV, FeLV
2. Drugs and Chemicals- NSAIDs, estrogen, sulfadiazine
3. Vaccines
4. Toxins
5. Immune-mediated marrow disease

Consumptive thrombocytopenias are seen with DIC and occur secondary to severe systemic inflammation.

What are the clinical features that are commonly seen with this disorder?

Peripheral thrombocytopenias range (50,000 to 150,000/ul)

Bone marrow megakaryocytes are normal in number

In dogs, often increased numbers of red cell schizocytes

1. Prothrombin time (PT)
2. Activated partial thromboplastin time (APTT)
3. Fibrin split products
4. Platelet count
5. Fibrinogen levels

If any three of the five are abnormal, DIC is considered to be present

Primary- idiopathic anti-platelet antibodies which cause accelerated destruction

Secondary- clinically identical to primary but occurs in association with any of a number of underlying disorders such as systemic immune disease, neoplasia, infectious disease, and vaccination.

1. Very low peripheral platelet counts (<50,000/ul)
2. Normal to increased numbers of bone marrow megakaryocytes

In some cases, antibodies can be directed against platelet precursors and this condition can't be differentiated from a hypoproliferative disorder.

1. Primary or essential
2. Secondary
3. Physiological

What are the caracteristics of each throbocytosis category?

Primary, secondary, and physiological

Primary- characterized by a persistent thrombocytosis (>100,000/ul), primarily a disorder of dogs presenting with a bleeding thrombosis.  May present with either regenerative or non-regenerative anemia

Secondary- Transiently increased platelet counts in patients with other primary disorders such as blood loss, gastrointestinal disease, fractures, immune-mediated disorders and others

Physiological- Increased mobilization of platelets from splenic and pulmonary pools, occurs as a result of exercise or epinephrine injection

Near normal platelet counts, normal PT APTT, normal fibrin split products, and normal fibrinogen levels.

The BMBT is prolonged

1. Uremia
2. Infectious (FeLV, Ehrlichia)
3. Snakebite
4. Hepatic disease
5. Various neoplasms
6. Drugs (NSAIDs, antibiotics, calcium channel blockers, dextrans, and colloids)

1. Von Willebrand's Disease (vWd)- most important
2. Basset Hound thrombopathia
3. Canine thrombasthenic thrombopathia of Otterhounds and Great Pyrenees
4. Spitz thrombopathia

• Type 1: 
• observed in many canine breeds and cats, mild bleeding tendency
• Type 2: 
• German Shorthair Pointers and Wirehaired Pointers, moderate bleeding tendency
• Type 3: 
• Scottish Terriers, Chesapeake Bay Retrievers, and Shetland Sheep Dogs, moderate bleeding tendency. vWf is usually 0% of normal