Bleeding disorders Flashcards
The process of coagulation requires
–Functioning platelets
–Functioning endothelium
–Coagulation factors
Balance
–Coagulant vs. anticoagulant factors
Imbalance
–Thrombosis
–Bleeding
What happens when you cut yourself?
Blood vessel damage
Disrupt endothelium
Exposure of
–Tissue Factor
–Collagen
Primary haemostasis
–Recruitment of platelets
Secondary haemostasis
–Activation of coagulation factors
Occur simultaneously
Primary haemostasis
Cut in the blood vessels exposes collagen and tissue factor
Also causes the exposure of von willebrand, which atrracts and binds platelets (through glycoprotein 1b_V-IX).
As platelets adhere to von willebrand, they become activated
Activation releases granular contents which cause aggregation and further activation of platelets
Secondary haemostasis
Activation of coaguation factors
Cascade of events:
- Initation - extrinsic pathway
- Propagantion- intrinsic pathway
- thromin generation
- fibrin producition - the clot
Initiation
ii- prothrombin
Prothrombinase complex- Xa + II (requires Va)
IIa- thrombin
thrombin activates XIII to cause cross linking of fibrin
Propagation
Thrombin feedsback to factor XI (becomes activated)
Interacts with IX and causes activation
Thrombin also activates factor VIIIa
VIIIa + IXa feedback to the prothrombinase complex and causes further fibrin to be made
Regulation
Antithrombin is a naturally occuring anti-coagulant that downreguates factor (7,10) (9,11) (10 +2) (9a + 2a)
Thrombomodulin is found on the endothelium. When thrombin is made it binds to thrombomodulin and then feedbacks and interacts with protein C. Protein C is activated to APC. APC plus another co-factor Protein S. Together these factors downregulate factor 5 and 8.
Tissue factor pathway inhibitor - downregulates pathway between tissue factor and factor VII
Fibrinolysis
Plasmin degrades fibrin
Plasmin comes from plasminogen (fibrin stimulates activation of plasminogen through tPA and uPA)
This process is regulated by alpha antiplasmin and PAI-1 and 2
Laborator analysis of coagulation
Assessment of primary haemostasis
–in vivo – Bleeding Time (cut the patient, measure clotting time)
–ex vivo – FBC (platelet count), platelet function
Assessment of secondary haemostasis
–Prothrombin time (PT)- measures the extrinsic system and the final common pathway- increased with warfarin
–Activated partial thromboplastin time (APTT)- measures the intrinsic and final common pathway - increased with heparin
–Thrombin clotting time (TCT) - measures the final part of the common pathway
–Individual coagulation factor assays
Samplle requirements
Plasma sample (blood thats not already clotted)
Prevent clotting
- citrate sample (chelates all calcium prevents clotting
- centrifugation (separates cellular component, add in synthetic phospholipid)
All results expressed
- seconds
- ration to normal plasma
What Clotting factors does PT measure?
Factors in extrinsic and common pathways
Factors VII
Factors X, V, II and fibrinogen
Acticated partial thromboplastin time (APTT) process?
Add
–Patient’s plasma
–Contact factor e.g. Kaolin or silica
–Phospholipid ( ‘partial thromboplastin’ )
Warm to 37°C
Add calcium
Time taken to clot
Normal range 26 - 38 secs
Ratio Patient/Average of 20 normals
Which clotting factors and clotting pathway does APTT measure?
–Factors in intrinsic and common pathways
–Factors VIII, IX, XI & XII
–and Factors X, V, II & Fibrinogen
Thrombin clotting time (TCT) process
Add at 37°C
–Patient’s plasma
–Bovine thrombin
–Less Calcium or phospholipid dependent
Time to clot
Normal 10-16 secs
Ratio Patient TT/Average of 20 normal TTs
What does TCT depend on and what is it inhibited by?
What does TCT depend on?
–How much fibrinogen is present in plasma
–How well that fibrinogen functions
But will also be prolonged by
–Inhibitors of thrombin (e.g. heparin, dabigatran)
–FDPs
Inhibitors of fibrin polymerisation (paraproteins
Simplified patterns of coagulation screen abnormality