2. Hemostasis
The process of blood clotting and
The process of blood clotting and
then the subsequent dissolution
then the subsequent dissolution
of the clot, following repair of the
of the clot, following repair of the
injured tissue, is termed
injured tissue, is termed
hemostasis
hemostasis.
.
4. Hemostasis - major events
1. Vascular constriction.
2. Platelets become activated by
thrombin and aggregate at
the site of injury, forming a
temporary, loose platelet
plug.
3. To insure stability of the
initially loose platelet plug, a
fibrin mesh (also called the
clot) forms and entraps the
plug.
4. The clot must be dissolved in
order for normal blood flow
to resume following tissue
repair.
5. HK = high molecular
wt. kininogen.
PK = prekallikrein.
PL = phospholipid.
6.
7. Endogeneous anticoagulants
• AT lll
– (binds to thrombin and prevents fibrinogen-fibrin)
• Heparin co-factor II
– (homologous with AT lll)
• Prot C
– (inhibits activity of factors V and Vll)
• Prot S
– (enhances the effect of protein C).
• TFPI
– (tissue factor pathway inhibitor - inhibits the
tissue factor-Vlla complex)
8. Vitamin K Dependent Factors
• Factors II, VII, lX, X.
• Protein C and Protein S
9. Role of the liver
Loss of liver parenchyma decreases:
– all coagulation factors - except F Vlll and von
Willebrand co-factor .
– physiologic inhibtors of the coagulation (AT lll,
Prot C and Prot S)
– components of the fibrinolytic system ( mainly
plasminogen, and a2 anti plasmines).
• Liver dysfunction induces:
– platelet dysfunction
– dysfibrinogenemia
– accelerated fibrinolysis (impaired clearance of
tissue plasminogen activators t-PA)
12. Approach to Bleeding
Approach to Bleeding
Disorders
Disorders
HISTORY
• Is the patient bleeding?
• Surrogate markers of bleeding
– declining hemoglobin
• Age of onset
• Surgical procedures
• Medications
– Aspirin, anticoagulants, etc.
• Birth & Family
13. Approach to Bleeding Disorders
Approach to Bleeding Disorders
•Petechiae,
• Echymoses,
• Menorrhagia
• GI bleeding
• Echymoses
• Late wounds bleeding
• Extensive hemorrhage
( joint spaces,
after immu.)
•
• Bleeding from
multiple sites in an
ill patient
Platelet
Disorder
Coagulation
Disorders
D.I.C.
14. Approach to Bleeding Disorders
Approach to Bleeding Disorders
If a patient has
tolerated tonsillectomy
and / or adenoidectomy
or extraction of multiple wisdom teeth
without major hemorrhage,
a significant
bleeding disorder
is unlikely.
15. Clinical aspects of bleeding
Clinical aspects of bleeding
• Do not blanch with pressure
(cf. angiomas)
• Not palpable
(cf. vasculitis)
Petechiae - (typical of platelet disorders)
Petechiae - (typical of platelet disorders)
17. Clinical aspects of bleeding
Platelet factor disorders Coagulation disorders
Site of bleeding Skin, Mucous
membranes (epistaxis,
gum, vaginal, GIT)
Deep in soft tissues
Petechiae Yes No
Ecchymoses
(“bruises”)
Small, superficial Large, deep
Hemarthrosis /
muscle bleeding
Extremely rare Common
Bleeding after
cuts & scratches
Yes No
Bleeding after
surgery or trauma
Immediate, usually mild Delayed (1-2 days),
often severe
Mucus membrane
bleeds
Spontaneous With trauma
18.
19. Investigations
Investigations
Platelet count
Platelet count 150,000 to 450,000 platelets per ml of blood.
150,000 to 450,000 platelets per ml of blood.
< 20,000 per mL - spontaneous bleeding
< 20,000 per mL - spontaneous bleeding
Bleeding time
Bleeding time Test for platelet function
Test for platelet function in
Normal : 2 - 5 minutes
Prothrombin
Prothrombin
Time
Time
measures the clotting activity of factors I, II, V,
measures the clotting activity of factors I, II, V,
VII, and X
VII, and X Normal : 12-15 seconds
Activated Partial
Activated Partial
Thromboplastin
Thromboplastin
Time
Time
Measures clotting activity of factors I, II, V, VIII,
Measures clotting activity of factors I, II, V, VIII,
IX, X, XI, and XII
IX, X, XI, and XII Normal : 25 - 39 sec
Factor assays
Factor assays Measure the amount of specific clotting factors
Measure the amount of specific clotting factors
FDPs
FDPs Fibrin degradation products
Fibrin degradation products
20. Activated partial thromboplastin time (aPTT
or APTT)
• is a performance indicator measuring the
efficacy of both the "intrinsic" (now referred
to as the contact activation pathway) and the
common coagulation pathways.
• It is also used to monitor the treatment effects
with heparin, a major anticoagulant.
21. aPTT - Interpretation
• Normal = 25 to 39 sec
• Prolonged APTT may indicate:
• heparin,
• direct thrombin inhibitors,
• a deficiency or inhibitor for factors in the intrinsic and
common pathway
• factors II, V, VIII, IX, X, XI, XII,
• lupus anticoagulant,
• vitamin K deficiency, or
• severe liver disease
22. Whole blood clotting time
• 5 ml of blood is placed in a glass container,
kept at body temperature and observed
• A clot should occur in 5 to 15 minutes
• Prolonged = Severe deficiency of any of the
coagulation proteins
• The clot should retract in 30 to 60 minutes
• Weak friable clot = hypofibrinogenaemia
• Early dissolution = enhanced fibrinolysis
(Inaccurate)
23. Prothrombin time
• The time taken for plasma to clot after addition of
tissue factor (obtained from animals) and calcium
to citrated blood.
• This measures the quality of the extrinsic pathway
(as well as the common pathway) of coagulation.
24. Prothrombin time
• The reference range for prothrombin time is
usually around 12-15 seconds;
• Prolonged
• Deficiencies of factors II, V, VII, X or
fibrinogen;
• Liver disease;
• Vitamin K deficiency and
• Oral anticoagulants (warfarin)
25. International normalized ratio
• Each manufacturer gives an ISI (International Sensitivity
Index) for any tissue factor they make. The ISI value
indicates how the particular batch of tissue factor
compares to an internationally standardized sample.
The ISI is usually between 1.0 and 1.4
• The INR is the ratio of a patient's prothrombin time to a
normal (control) sample, raised to the power of the ISI
value for the control sample used.
26. Thrombin time
• Time to clot formation after the addition of
thrombin to citrated blood
• Prolonged by
• Heparin,
• Direct thrombin inhibitors,
• Fibrin degradation products (FDPs),
• Paraproteins, and
• Fibrinogen deficiency (both qualitative and
quantitative)
27. Bleeding time - Ivy method
• A blood pressure cuff is placed on the upper arm and
inflated to 40 mm Hg. A lancet is used to make a stab
wound on the underside of the forearm.
• The time from when the stab wound is made until all
bleeding has stopped is measured and is called the
bleeding time.
• Every 30 seconds, filter paper or a paper towel is
used to draw off the blood.
• Normal values fall between 2 - 5 minutes depending
on the method used
28.
29. FDPs
• Fragments resulting from the action of
plasmin on fibrin or fibrinogen
• Reflect high fibrinolysis states (such as
DIC) when they are elevated
30. Platelet Count
• In an adult, a normal count is about
150,000 to 450,000 platelets / µL of blood.
• Platelet levels fall below 20,000/µL,
spontaneous bleeding may occur and is
considered a life-threatening risk.
• Increased platelet counts (thrombocytosis)
• Myeloproliferative disorder
31. Others Tests
• Von Willebrand factor antigen (vWF:Ag):
immunoassay for circulating vWF.
• Von Willebrand factor activity (vWF:RCo):
measures the functional ability of a patient's
vWF to agglutinate platelets in the presence of
Ristocetin.
• Factor VIII C activity: is functional assay for
factor VIII. It is measured by mixing normal
plasma with factor VIII-deficient plasma
• Platelet function studies
• Bone marrow examination – plt
32. Laboratory Evaluation of the Coagulation
Pathways
Partial thromboplastin time
(PTT)
Prothrombin time
(PT)
Intrinsic pathway Extrinsic pathway
Common pathway
Thrombin time
Fibrin clot
Thromboplastin
Tissue factor
Phospholipid
Calcium
Thromboplastin
Tissue factor
Phospholipid
Calcium
Surface activating agent
(Ellagic acid, kaolin)
Phospholipid
Calcium
Surface activating agent
(Ellagic acid, kaolin)
Phospholipid
Calcium
Thrombin
Thrombin
34. Correction Tests
Only PTT abnormal : XI, IX & VIII
(XII never presents clinically)
Abnormal PTT
corrected by
Plasma Adsorbed Serum
VIII Yes No
IX No Yes
39. von Willebrand Disease
An inherited bleeding disorder described by Finnish Physician
Erik Adolf vonWillebrand
Low levels of a protein called vonWillebrand
factor that helps the blood to clot
VonWillebrand factor that doesn’t work properly
40. Platelet Activation and
von Willebrand Factor (vWF)
In order for hemostasis to occur, platelets must
adhere to exposed collagen, release the contents
of their granules, and aggregate.
The adhesion of platelets to the collagen
exposed on endothelial cell surfaces is mediated
by vonWillebrand factor (vWF).
41. The function of vWF is to act as a bridge between
a specific glycoprotein on the surface of platelets
(GPIb/IX) and collagen fibrils.
vWF binds to and stabilizes coagulation factor
VIII.
Binding of factorVIII by vWF is required for
normal survival of factorVIII in the circulation.
Platelet Activation and
von Willebrand Factor (vWF)
42. Type 1
Low level of vonWillebrand factor.The level of factorVIII may also
be lower than normal
Mildest and most common form of the disease.
About 3 out of 4 people diagnosed with vWD have type 1 disease.
Type 2
Defect in vonWillebrand factor causes it to not work properly.Type
2 is divided into 2A, 2B, 2M, and 2N. Each is treated differently, so
knowing the exact type is important.
Type 3
No vonWillebrand factor and very low factorVIII.
Type 3 is severe and very rare.
von Willebrand Disease
43. von Willebrand Disease
Incidence
roughly about 1 in 100 individuals.
Because most forms are rather mild, they are detected
more often in women, whose bleeding tendency
shows during menstruation.
It may be more severe or apparent in people with
blood type O.
44. Genetics
vWF gene is located on chromosome twelve
(12p13.2).
o Types 1 and 2 are inherited as autosomal dominant
traits and
o type 3 is inherited as autosomal recessive.
o Occasionally type 2 also inherits recessively.
von Willebrand Disease
46. Weibel-Palade bodies
Organelles in the endothelial cells
There are two major constituents
1. von Willebrand factor (vWF), a
multimeric protein involved in blood
coagulation
2. The second is P-selectin - binds to
passing immune cells (leukocytes).
47. Manifestations:
Bruising that's unusual in location or frequency
Abnormal menstrual bleeding
Bleeding in the mucous membranes
Excessive or prolonged bleeding after a tooth
extraction or tonsillectomy
von Willebrand Disease
48. Bleeding time
Factor VIII level test (factor VIII coagulant)
von Willebrand factor antigen test (factor VIII antigen) - which
measures the amount of von Willebrand factor. ( mild if a person
has 20% to 40% of the normal, severe if the amount is less than 10% of
normal. )
Ristocetin co-factor activity test
measures how well the von Willebrand factor is working
von Willebrand factor multimers test - to classify the type of
vWD
Platelet function tests
which determine how well the platelets work and help identify the type of vWD
or the presence of another disorder
Tests may need to be done more than once because these levels may rise
and fall over time in an individual.
Investigations
49. Treatment:
No regular treatment
Prophylactic treatment is sometimes given for
patients are scheduled for surgery.
They can be treated with human derived medium
purity factorVIII concentrates complexed to vWF
Mild cases - treated with desmopressin (1-desamino-
8-D-arginine vasopressin, DDAVP)
Rises patient's own plasma levels of vWF by inducing
release of vWF stored in theWeibel-Palade bodies in the
endothelial cells
von Willebrand Disease
