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Hematology Block 2 > Hemostasis > Flashcards

Hemostasis Flashcards

1
Q

What 3 broad actions need to happen for a clot to form?

A

Vessel constriction

Platelet plug formation

Fibrin formation

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2
Q

The normal hemostatic system limits blood loss by precisely regulated interactions between components of the:

A

vessel wall, circulating blood platelets, and plasma proteins

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3
Q

___, ___, and ___ are common clinical manifestations of many diseases.

A

Hemorrhage, intravascular thrombosis, and embolism

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4
Q

Formation of a hemostatic plug (thrombus or clot) is derived from platelets and fibrin strands, in which ____ are trapped.

A

RBC’s/WBC’s

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5
Q

Define hemostasis:

A

Hemostasis is the arrest of bleeding following vascular injury

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6
Q

Hemostasis is dependent on intricate interactions between:

A

–Platelet adhesion and aggregation,

–Endothelial cell function,

–Blood coagulation system

–Clot lysis (fibrinolysis) system.

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7
Q

The components that comprise platelet aggregation/ endothelium, coagulation and fibrinolysis also termed:

A

primary, secondary and tertiary hemostasis, respectively

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8
Q

To stabilize platelet plug you need ____. In a hemophiliac, you can’t stabilize platelet plug so the patient continues to bleed.

A

fibrin

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9
Q

Blood vessels are considered to be a(n) ______ surface, to prevent a clot from forming on their surface.

A

anticoagulant

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10
Q

Platelets help maintain the ____ of the vessel lining, and they ___ any rupture in the circulatory vessels.

A

Platelets help maintain the integrity of the vessel lining, and they plug any rupture in the circulatory vessels.

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11
Q

What is a normal platelet count?

A

Between 150-450x10^9/L

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12
Q

Normal platelet lifespan is:

A

7-10

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13
Q

Coagulation factors interact in a highly ordered sequence with the ultimate object of converting _____ to insoluble ____ that stabilizes the primary hemostatic plug.

A

Coagulation factors interact in a highly ordered sequence with the ultimate object of converting soluble fibrinogen to insoluble fibrin that stabilizes the primary hemostatic plug.

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14
Q

Which coagulation factors are zymogens/active enzymes?

A

Vitamin K-dependent – factors II, VII, IX, X

Vitamin K-independent– factors XI, XII, and XIII

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15
Q

What are important protein and non-protein cofactors in secondary hemostasis?

A

Protein: Factor V, factor VIII, tissue factor, and von Willebrand factor (vWF)

Non-protein: Calcium (in blood) and phospholipid surfaces (from cells)

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16
Q

Which two coagulation factors are especially important in controlling coagulation?

A

Factor VII and Factor VII

These have short half-lives and are present in small amounts in the blood

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17
Q

In screening tests of coagulation, blood is collected and kept from clotting by a ____ sequestering agent

A

calcium-sequestering (e.g. citrate)

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18
Q

Coagulation is initiated in screening tests by adding an activating agent such as:

A

calcium and phospholipid

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19
Q

Routine coagulation tests include:

A

Prothrombin time (PT)

Activated Partial Thromboplastin Time (aPTT)

Thrombin Time (TT) = Thrombin clotting time (TCT)

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20
Q

The Thrombin Time (TT) test measures what?

A

The conversion of fibrinogen to fibrin.

Add thrombin to the tube to directly measure the conversion, taking no other factors into account.

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21
Q

How is a Thrombin Time test performed?

A

Thrombin is added to a citrated plasma tube of blood, and the time until a clot forms is recorded (in seconds).

NOTE: calcium and phospholipid are NOT required for TT

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22
Q

What causes a prolonged TT?

A

1. Low fibrinogen (hypofibrinogenemia)

2. Abnormal fibrinogen (dysfibrinogenemia)

  • inherited
  • acquired (severe liver disease)

3. Inhibitor of added thrombin

  • direct inhibitor; e.g. argatroban, dabigatran
  • indirect inhibitor; heparin
  1. Something that interferes with fibrin polymerization
  • paraproteinemia (from myeloma or Waldenstroms)
  • very high levels of fibrin degradation products
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23
Q

What drugs are direct inhibitors of added thrombin in a TT test?

A

Argatroban

Dabigatran

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24
Q

What drugs are indirect inhibitors of thrombin, causing a prolonged TT?

A

Heparin

(causes problems by interacting with antithrombin)

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25
Q

How is the Prothrombin Time test performed?

A

Thromboplastin and Calcium are added to citrated plasma. The time until a clot forms is recorded.

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26
Q

What are the essential components of the secondary hemostasis coagulation cascade?

A

The extrinsic pathway consists of Factor VII and tissue factor with tissue factor considered to be “extrinsic” to the bloodstream. Factor VII, when activated, forms a complex with tissue factor that converted factor X to activated factor X (factor Xa). The intrinsic system, consisting of factors XII, XI, X and IX, leads to the formation of a complex of factor IXa with its cofactor, factor VIIIa, which in the presence of phospholipid and calcium can also convert factor X to Xa. Factor Xa, as the enzyme, forms a complex with its cofactor, factor Va, and rapidly converted prothrombin to thrombin. This reaction requires a phospholipid surface and calcium. Once thrombin is formed, fibrinogen is converted to fibrin monomers that polymerize to form a fibrin clot. Thrombin activates factors V, VIII, XI and XIII in important feedback steps.

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27
Q

The thromboplastin reagent contains WHAT?

A

Tissue Factor and Phospholipid

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28
Q

What causes a prolonged PT?

A

•Anything that prolongs the TT (BUT the PT is much less sensitive than the TT to the presence of heparin, abnormal fibrinogen, and FDPs)

•Anything that lowers levels or inhibits the common pathway factors

  • Factor X
  • Factor V
  • Factor II (prothrombin)
  • Fibrinogen

•And also low levels of FVII, which can arise:

  • Congenital
  • Acquired
    • Deficiency of Vitamin K
    • Vitamin K inhibitors
    • DIC
    • Liver disease
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29
Q

What are the common pathway factors?

A

Factor X

Factor V

Factor II (prothrombin)

Fibrinogen

30
Q

What are the vitamin K dependent factors?

A

Factor II

Factor VII

Factor IX

Factor X

Protein C and S

(these are inserted via their gamma carboxyl groups into the activated platelet membrane)

31
Q

What are sources of Vitamin K?

A

Diet (leafy green veggies)

Gut flora

32
Q

What are some causes of Vitamin K deficiency?

A

Dietary

Antibiotics

Fat malabsorption

Being a newborn

33
Q

What’s an INR?

A

•INR = International Normalized Ratio. Given with all PT results.

  • This was developed as a reporting tool to allow different measurements from different laboratories to be more comparable.
  • This is calculated as the ratio of the patient’s PT over the mean normal PT—raised to an exponent called the ISI; the ISI is given for each new batch of thromboplastin.
  • Normal value for an INR is 1.
  • Technically, this is only supposed to be used in patients on warfarin, but the liver docs have gotten hold of this and use an elevated INR as part of their cirrhosis scoring system
34
Q

How is an activated partial thromboplastin time test performed?

A

An activator is added to blood, followed by “partial” thromboplastin and calcium. Time is recorded until a clot forms.

35
Q

What are the activators used in the aPTT tests?

A
  • Substance that provides negative charges to activate the contact system (that’s HMWK, PK and Factor XII)
  • Things that can do this include kaolin, celite, and ground glass
36
Q

What’s missing in the “Partial thromboplastin” that’s there in a complete thromboplastin?

A

•The partial thromboplastin is missing tissue factor.

•It DOES have phospholipid

37
Q

What causes a prolonged aPTT?

A

•Problems with factors in the common pathway

  • Factor II, V, X
  • Fibrinogen

•Problems with the contact factors

  • Factor XII, HMWK, PK

•Problems with

  • Factor XI—Hemophilia C
  • Factor IX—Hemophilia B
  • Factor VIII—Hemophilia A

•Warfarin in excess, or severe vitamin K deficiency (due to their effects on IX, X, and II)

•Heparin (unfractionated)

•Lupus Inhibitor (AKA Lupus anticoagulant)

38
Q

Warfarin or severe Vitamin K deficiency can cause a prolonged aPTT - why?

A

They affect Factor IX, X, and II

39
Q

What is the Lupus inhibitor? (relevent for aPTT tests)

A
  • Some people make an autoantibody directed against phospholipid.
  • When this antibody prolongs coagulation reactions in the test tube—and this prolongation is blocked by addition of MORE phospholipid in the reaction mix—we call this a LUPUS INHIBITOR.
  • We will re-visit this in the thrombosis lecture
  • Confusing things
    1. Though the aPTT can be prolonged—this antibody doesn’t cause bleeding. In fact—in can lead (paradoxically) to abnormal thrombosis. Weird.
  • Though we call it a lupus inhibitor—most people who have this don’t have lupus, and most people with lupus don’t have this antibody. Also weird.
40
Q

What is the purpose of a Mixing Study?

A

Helps differentiate between the two broad causes of a prolonged PTT -

  • Factor deficiency (something’s missing)
  • Inhibitor (something’s interfering)
41
Q

Describe the process of a Mixing Study:

A

Perform an initial aPTT - if prolonged, then…

Take the patient’s plasma and mix it 1:1 with normal plasma, then repeat the aPTT.

42
Q

How are results of a Mixing Study evaluated?

A

If the clotting times REMAIN prolonged (even slightly) - Inhibitor present

If the clotting times NORMALIZE - Factor deficiency

43
Q

A patient has a PTT of 100 sec (25-35). 1:1 mix aPTT is 45 sec. What is the cause of the patient’s long aPTT?

A

Inhibitor

(Remember Dr. Ma’s tiger mom)

44
Q

In regards to factor deficiencies, the higher up in the PTT pathway you go, the ____(lower/higher) the PTT value. Also, the ___ (less/more) clinical significance it has in terms of bleeding risk.

A

In regards to factor deficiencies, the higher up in the PTT pathway you go, the higher the PTT value. Also, the less clinical significance it has in terms of bleeding risk.

45
Q

What might be the problem in cases where BOTH the PT and PTT are prolonged?

A
  • Deficiency of common pathway factor
  • Excess of warfarin
  • Excess of heparin
  • Multiple factor deficiencies:
  • Severe liver disease
  • Severe DIC
46
Q

Which clotting factor is NOT involved in the aPTT assay?

Factor VII

Factor VIII

Factor IX

Factor X

A

Factor VII

47
Q

Abnormalities of which factor will prolong the TCT?

Prothrombin

Factor V

Fibrinogen

Factor XI

A

Fibrinogen

48
Q

What occurs during primary hemostasis?

A
  • Platelet interactions with the injured vessel wall.
  • NOT—formation of a fibrin clot
49
Q

Describe the process of the Ivy Template Bleeding Time test:

A
  • Inflate BP cuff on upper arm to 40 mm Hg
  • Use a standard-sized small blade to incise the skin
  • Blot the fresh blood away every 30 seconds (This prevents fibrin clot formation from playing a role).
  • Time until bleeding stops
50
Q

What are some limitations of the bleeding time test?

A
  • Invasive
  • Time consuming
  • Low sensitivity
  • Poorly reproducible
  • Does not correlate with surgical bleeding
  • Leaves a scar
51
Q

How does a Platelet Function Analyzer test work?

A

Whole blood is sucked through the machine (mimicking high shear - like that in an arteriole).

Eventually, platelets plug up the grid (which is coated with collagen and contains a platelet stimulus like ADP or epi)

Closure time is measured (time it takes for flow to stop)

52
Q

What are the advantages of a PFA-100?

A
  • Needs only a small volume of blood
  • More reproducible
  • Rapid and automated—not a lot of skill needed
53
Q

What makes a PFA-100 test prolonged?

A
  • Low platelet count (<100 x 109/L)
  • Low hemoglobin (<10 g/dL)
  • Low von Willebrand factor (qualitative or quantitative problems)
  • Congenital
  • Acquired

•Abnormal platelet function:

  • Congenital
  • acquired
54
Q

Platelets have a vital contribution to hemostasis including the:

A

initial event of platelet adhesion to the vessel wall, followed by platelet aggregation and release

55
Q

Activated platelets release granule contents, including:

A

ADP

Thromboxane A2 (TxA2)

These recruit more platelets and promote aggregation

Also release some coagulation factors

56
Q

Platelet glycoprotein IIb/IIIa is a(n) _____, which adheres to ____, enhances aggreation, and stabilizes the _____

A

Platelet glycoprotein IIb/IIIa is a(n) integrin receptor, which adheres to fibrinogen, enhances aggreation, and stabilizes the thrombus.

57
Q

The growing platelet thrombus is stabilized by ____

A

fibrin

58
Q

_____ cells release prostacyclin (PGI2) and nitric oxide (NO) to inhibit further platelet aggregation

A

Endothelial cells

59
Q

_____ have a critical role in primary hemostasis. _____ are essential for secondary hemostasis.

A

Platelets have a critical role in primary hemostasis. Blood coagulation proteins are essential for secondary hemostasis.

60
Q

What are the stages of primary, secondary, and tertiary stages of hemostasis?

A
61
Q

The extrinsic pathway is triggered by the:

A. phospholipid membrane

B. tissue factor

C. calcium

D. factor VIIa

E. all of the above

A

All of the above!

62
Q

The common pathway begins with which coagulation factor and is activated by which protease?

A

A. Factor X activation by factor VIIa/tissue factor

63
Q

The stable fibrin clot is formed when fibrin-stabilizing factor (factor ___), a transaminase, covalently links the adjacent domains of three fibrin monomers, the _____ domains, through the __ chains.

A

The stable fibrin clot is formed when fibrin-stabilizing factor (factor XIII), a transaminase, covalently links the adjacent domains of three fibrin monomers, the D-D-E domains, through the gamma chains.

64
Q

In addition to cleaving fibrinogen –> fibrin, Thrombin also activates ____ to ____

A

Factor XIII to Factor XIIIa

65
Q

The fibrinogen molecule is formed from three protein molecules (___, ___, and ___) that are present in the molecule in pairs. The central part of the molecule is referred to as the ___ domain and the two distant ends are the ___ domain.

A

The fibrinogen molecule is formed from three protein molecules (alpha, beta, and gamma chains) that are present in the molecule in pairs. The central part of the molecule is referred to as the E domain and the two distant ends are the D domain.

66
Q

Thrombin cleaves ____ from fibrinogen to form a fibrin monomer. Elaborate.

A

Thrombin cleaves two small activation peptides from fibrinogen to form a fibrin monomer.

Fibrinopeptide A - 16 AAs

Fibrinopeptide B - 14 AAs

67
Q

____ is the degradation product of cross-linked fibrin; it reflects ongoing activation of the hemostatic system.

A

D-dimer

68
Q

Healthy individuals have a ___ D-Dimer level

A

minimal

69
Q

Elevated D-dimer levels reflect WHAT. How is this information clinically useful?

A

Reflect ongoing activation of the hemostatic and thrombolytic system. Useful in:

  • Evaluation of thrombus formation
  • Ruling out deep vein thrombosis
  • Monitoring anticoagulative treatment
  • Disseminated intravascular coagulation (DIC)
70
Q

Which coagulation complex is the most likely in vivo “trigger” to initiate blood clotting?

A. FXIa/FIX

B. FIXa/FVIIIa

C. Tissue factor/VIIa

D. FXa/prothrombin

A

C. Tissue factor/VIIa

71
Q

How is anti-coagulation achieved?

A

Tissue factor pathway inhibitor

coagulation protease inhibitors

protein C system

fibrinolysis

Hematology Block 2 (7 decks)

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