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Clin Path Test 2 > Platelets and Hemostasis > Flashcards

Platelets and Hemostasis Flashcards

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1
Q

Thrombocytosis:

Def

Causes

A

Def: increased platelets

Causes:

  1. inflammation (IL-6, TNF-alpha, IL-1) => cause inc thrombopoietin production
  2. Iron deficiency anemia
  3. Cushing’s disease 4. Steroid therapy
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2
Q

What doesn’t cause a thrombocytopenia (usually)

A

hemorrhage bleeding

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3
Q

Platelets

A

Have calcium in them (most clotting rxns need Ca2+)

Use purple top tube with K/EDTA

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4
Q

Purple top tube

A

Has K/EDTA EDTA => chelates Ca2+ and inhibits clotting

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5
Q

Calcium in clotting

A

Positively charged

Mediates binding of coagulation factor enzyme complexes via their negatively charged residues to negatively charged phospholipid surfaces of platelets

Ca is a bridge of positivity, allows platelets to act as scaffolds for clotting reactions

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6
Q

Alpha granules in platelets

A

Adhesion proteins (like Von Willebrands factor)

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7
Q

Common breed for Von Willebrand’s factor deficiency

A

Dobermans

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8
Q

Cat Platelets

A

Larger with a higher mean platelet volume (MPV) Especially sensitive to activation during blood sample collection

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9
Q

Snakes

A

Have thrombocytes Their platelets are very large and are an actual cell type

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10
Q

How to do a platelet estimate

A
  1. Count number of platelets in 10-100X oil immersion fields and average. 2. For dogs average count in 10 fields x 15,000/microLiter 3. For cats average count in 10 fields x 20,000/microLiter
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11
Q

Hemostasis

A

The arrest of bleeding.

Requires integrated response from blood vessels:

  1. endothelial cells
  2. collagen
  3. smooth muscle cells
  4. fibroblasts…..

and platelets, circulating clotting factors, and fibrinogen becoming fibrin.

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12
Q

Primary Hemostasis

A

Peripheral vasoconstriction occurs

Blood starts flowing again after momentary stoppage

Platelets start degranulating and releasing Ca2+ to form a platelet plug

(Endothelial defect exposes subendothelial collagen)

End result = platelet plug

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13
Q

Secondary Hemostasis

A

Stimulation of the coagulation system

Thrombin (Factor 2a) converts fibrinogen (Factor 1) to the active fibrin (Factor 1a)

Fibrin is incorporated into the clot and clot is stabilized

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14
Q

Coagulopathy

A

Excessive bleeding due to abnormal function/lack of presence of a coagulation factor.

Defect in secondary hemostasis usually leading to more severe bleeding than a platelet or primary hemostasis problem.

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15
Q

Coagulopathies lead to

A

Hemoabdomens, hemothoraxes, hemarthrosis, hematuria, and of course petechiae and purpura.

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16
Q

If there is a clot in the blood tube….

A

Don’t trust values from a hematology analyzer.

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17
Q

Automated platelet counts in cats….

A

Are NOT reliable.

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18
Q

Platelet counts

A

Lower in King Charles Spaniels and greyhounds.

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19
Q

King Charles Spaniels have a high prevalnce of

A

inherited asymptomatic thrombocytopenia with macrocytic platelets:

60-80,000 platelets can be normal

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20
Q

MPV

A

Large platelets are often young platelets

Platelet clumps will falsely decrease a plately count and falsely increase the MPV

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21
Q

Increased MPV

A

Seen in enhanced thrombopoiesis in response to thrombocytopenia

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22
Q

Thrombocytopenia often leads to

A

Petechiae, purpura, or ecchymoses.

-usually when less than 50,000/microLiter or less than that

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23
Q

Facial petechiae around the eyes

A

May be caused by a tight leash or a rabies pole.

Do a blood smear to look for platelets.

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24
Q

In a thrombocytopenic animal…

A

Do not use the jugular vein for blood, too close to the heart.

Do not poke organs, they may not stop bleeding.

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25
**Hall mark of tick-borne disease**
**Thrombocytopenia**
26
Evan's syndrome
Immune mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP) simultaneously.
27
**Thrombocytopenia differentials**
**1. Decreased platelet production.** **2. Increased platelet consumption.** **3. Increased platelet destruction (most common cause)**
28
**Decreased platelet production**
**To assess do a bone marrow aspirate to look for sufficient platelet precursors, megakaryocytes.**
29
**Not enough megakaryocytes**
**Myelopthisis: space occupying lesion of bone marrow** **Myeloproliferative diseases: Aplastic anemia, bone marrow not making anything ie: estrogen knocks out bone marrow in ferrets and dogs**
30
**Increased platelet consumption**
**DIC and thrombosis, vasculitis, hemangiosarcoma in dogs.** **These animals will likely show changes in PT/PTT since platelets used up for clotting.**
31
**Increased platelet destruction**
**Most common cause of thrombocytopenia** Primary immune thrombocytopenia (ITP) Secondary immune-mediated thrombocytopenias (drugs, infectious agents, neoplasia, SLE)
32
**Vitamin K dependant clotting factors**
**2, 7, 9, 10**
33
**Vitamin K works by**
**inhibiting the enzyme, vitamin K epoxide reductase in the liver** **-makes these factors hypofunctional**
34
**Which clotting test is prolonged first?**
**PT expected to be prolonged before PTT due to the short half-life of Factor 7.** **Prolongation of PTT first is possible as well, depending on the species involved.** **For the test think PT!!!!**
35
Anticoaculation proteins
Anti-thrombin Alpha 2 macroglobulin
36
Anti-thrombin
Stops thrombin from acting. Thrombin converts fibrinogen to fibrin Heparin keeps thrombin and anti-thrombin together
37
PLE
Protein losing enteropathy: Low albumin and low globulin
38
PLN
Protein losing nephropathy. Low albumin only.
39
Low antithrombin
Hypercoagulable state DIC PLN PLE
40
Phase of clotting
1. Vascular phase: Exposure of subendothelial matrix and exposure of tissue factor (TF) 2. Platelet phase: Adhesion, activation, shape change, secretion (degranulation), aggregation =\> Platelet adhesion: Von Willebrands factor is how platelets adhere to each other and the vasculature (deficiency in dobermans)
41
Desmopressin
Stimulates transient release of von Willebrand factor from the endothelial cells.
42
von Willebrand factor
synthesized and released from endothelial cells and platelets
43
Major platelet agonists
PAF (Platelet activating factor)-made by cells of immune system, this is one way that inflammation and coagulatio are linked.
44
**Intrinsic clotting cascade**
**12, 11, 9, 8 (PTT test) + common pathway**
45
**Extrinic clotting cascade**
**VII and TF (PT test) + common pathway**
46
**Common pathway**
**10, 5, 2, 1**
47
How do you evaluate platelet function?
BMBT (buccal mucosal bleeding test)
48
**Which clotting factor has the shortest half life?**
**Factor VIIa**
49
**Which clotting factor test would be prolonged if an animal got into a vitamin K rodenticide?**
**The animal will have a prolonged PT.** **VIIa is an extrinsic pathway factor so use PT.** **2, 7, 8, 10 all need vitamin K**
50
Prolonged PT and PTT
Common clotting pathway is the problem
51
Platelet function disorder
von WIllebrand factor deficiency
52
Blood tube to test PT/PTT
Blue top=citrated plasma
53
Function of factor XIIIa
Cross links fibrin
54
Causes of fibrinolysis
Occurs from crotalase in Eastern Diamondback rattlesnake venom
55
Cryoprecipitate contains
Von Willebrand factor Fibrinogen Factor 8 Factor 13
56
Cats and platelets...
Cats have largest and most activated platelets of any species.
57
**Thrombocytosis**
Increased platelets. Most common cause: Inflammation IL-6 leads to increased thrombopoietin
58
Iron deficiency anemia
1. Seen with cushings (inc adrenal secretion of cortisol) or prednisone =\>cortisol is immunosuppressive and prevents macs from phagocytosing old platelets 2. Rebout response to thrombocytopenia. 3. Withing one week following a splenectomy
59
Hyper coagulable state
More likely to have a clot Initial reactions that lead to thrombosis and DIC Anti-thrombin deficiency
60
Mast cells in circulation in a dog
IMHA, inflammation, or **Parvo virus** Likely not from a mast cell tumor
61
Mast cells in circulation in cats
Likely has a mast cell tumor in spleen, liver, or intestines (visceral organs)
62
**Snake venoms**
**Degrade fibrinogen** **=\>increase FDPs, not increased D-dimers** **=\>sperocytes may be seen in blood film**
63
**Increased FDPs**
Snake bite Breakdown of fibrin monomers by plasmin before they've been crosslinked, before Facto13a has crosslinked the fibrin. =\> these usually removed from circulation by the liver. Doesn't necessarily mean activation of clotting cascade with active lysis of cross-linked fibrin clot.
64
Presense of D-dimers Increased D-Dimers
Means the active breakdown of covalently, crosslinked (via Factor 13a) fibrin Active coagulation and breakdown of clots
65
**D-dimers specific for**
**Thrombus formation because it only occurs when soluble fibrin has been crosslinked by Factor 13a and plasmin has cleaved this stable fibrin to form this unique D-dimers**
66
**Fibrinogen**
**Acute phase protein.** **Increases with inflammation.** **May be the only early sign of inflammation in large animals.** **Inflamed animals without elevated fibrinogen** **=\> liver not making fibrinogen (liver failure)** **=\> or fibrinigen getting converted to fibrin (look for other signs of DIC**
67
**Other signs of DIC**
**Low fibrinogen** **Increased D-dimers AND increased FDPs** **Fragmentation morphologies** **=\> acanthocytes** **=\> schistocytes** **=\> keratocytes** **Consumption of platelets (thrombocytopenia)**
68
**DIC treatment**
**PLASMA NOW** **Then find underlying cause of DIC**
69
Hemophilia A
Factor 8 deficiency
70
Hemophilia B
Factor 9 deficiency
71
Factor 12 and testing
Abscense doesn't cause bleeding disorders =\> Not necessary for secondary hemostatis in vivo =\> Missing in some cats and other species =\> Will cause an increase in PTT b/c test is in a plastic tube, and assess for 12, 11, 9, 8, 10, 5, 2, and 1
72
**If PT/PTT are both prolonged**
**Think common pathway** **Factors 10, 5, 2 (pro-thrombin to thrombin) and 1 (fibrinogen to fibrin)**
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Clin Path Test 2 (3 decks)

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