Haemostasis - 143 Flashcards
APPT time is which pathway?
Intrinsic
PT time is which pathway?
Extrinsic
Baby with life threatening nose bleed. All tests normal except slightly prolonged bleeding time. What is wrong?
Interference with platelet functioning. THrombo-asthenia
30 year old male, spontaneous swollen knee. APTT long
Haemophilia A
36 year old pregnant women, recent SOB and chest pain. Prolonged thrombin time, prolonged APPT. What is wrong?
Heparin treatment
7 yr boy, petechiae.
ITP
2 week premature baby with IC bleeding. Prolonged APTT, OSPT prolonged
Vitamin K deficiency
What is primary hemostasis? Describe the stages
The formation of a platelet plug. Starts with vasoconstriction of the vessel, followed by platelets sticking to the exposed collagen forming the ‘plug’
How are platelets activated?
Unactivated platelets bind vWF in the subendothelial matrix (via GPlb receptors), which activates them, resulting in the release of their granules and the expression of phospholipids and GPIIb/IIa
What happens in secondary hemostasis?
The fibrin clot is formed and the coagulation cascade is initiated.
What initiates the coagulation cascade?
FV and FVIII binding tissue factor (TF)
What test is done if you want to assess the intrinsic pathway?
APTT
What test is done if you want to assess the extrinsic pathway?
PT
What is the end of the coagulation cascade?
Fibrinogen being cleaved to fibrin (FIa) by thrombin (FIIa)
How might a patient with a disorder of primary hemostasis present?
- Site of bleeding = mucous membrane & skin
- Bleeding after minor cuts
- Petichae
- Small/absent echymoses
- Bleeding after surgery is mild & instant
How might a patient with a disorder of secondary hemostasis present?
- Site of bleeding = soft tissues, joints
- Bleeding after minor cuts not normal
- NO petichae
- Echymoses are large
- Muscle haematomas common
- Bleeding after surgery delayed and severe
Name some disorders of 1 hemostasis
- Hereditary haemorrhagic telengiectasia (autosomal dom)
- Henoch-Schonlein purpura - vasculitis (acquired - if no haematuria you don’t treat)
Name some coagulation disorders of 2 hemostasis
- Haemophilia A (x-linked) - FVIII.
- Haemophilia b (christmas disease) - FIX
- Acquired diseases, e.g. liver disease, vitamin K deficiency
What is the pathogenesis of vWD?
Patients are lacking vWF, which means the platelets cannot attach to the epithelium. It would show an abnormal APTT. Autosomal dominant
Where are clotting factors produced?
Produced in their inactive form in the liver and secreted into the blood
What is the role of vWF?
Carries FVIII in the blood
What is the role of fibrin?
It stabilises the clot. Fibrinogen is the most abundant clotting factor
What is the first phase of the extrinsic coagulation cascade?
TF + VII
What could be the cause behind a long TT?
Patient has no/low fibrinogen
Something is inhibiting the thrombin, e.g. heparin
What could be the cause behind a long APTT?
If FXII is low or missing -> this does NOT cause bleeding disorders though
FVIII, FIX, FXI, FXII need to be assessed.
Which clotting factor do you need to look at if a patient has a long TT and APTT?
FX
What does anti-thrombin inhibit?
Thrombin and FXa
Describe the protein C system
Protein C molecules activate Protein S. This then inhibits FVa and FVIIIa.
Note: protein C needs vitamin K for synthesis
When would you do a D-dimer?
Patient is at low risk for DVT
How is a DVT treated?
LMWH
What investigations would you do to diagnose a PE?
ABG, ECG, CXR, USS, D-dimer
Which coagulation factors rely on vitamin K?
FII, FVII, IX, X
Name an anti-fibronolytic drug and what it might be used for
Tranexamic acid, stabilises clot. Used when there is bleeding, e.g. epistaxis, menorrhagia
Name a vitamin K antagonist
Warfarin
