- Created by: ellenrobinson
- Created on: 19-05-19 22:41
Bleeding defects may result from:
• vascular defects (weak vessels – leak)
• decreased platelet number (thrombocytopenia)cau
• decreased platelet function
• decreased coagulation
· Normal platelet count = 150 – 400 x 109/L
· Thrombocytopenia: Blood platelet count of <150 x 109/L
- Failure of marrow production
- Shortened lifespan
- Dilution by massive blood transfusion
Idiopathic thrombocytopenic purpura
Idiopathic = unknown cause
Thrombocytopenic = low platelet count
Purpura = 3mm-1cm purple blemishes indicative of bleeding under the skin
- Sudden onset in children, often after trivial illness.
- IgG may attach to a viral Ag absorbed onto the platelet surface.
- The antibodies may attack platelets due to a virus binding to the platelet during infection
- Gradual onset in adults (3F:1M) (no previous viral infection)
- Autoantibodies against platelet membrane antigens detectable in ~80% patients
- Spontaneous remission rare, lifelong condition
Diagnosis : [Hb] and WBC counts typically normal. Blood film shows reduced platelet numbers (often large). Bone marrow normal or increased numbers of megakaryocytes.
– Often just observation as it normal goes away within 6 weeks
– Splenectomy ( spleen removal)
– High dose intravenous immunoglobulin therapy
TTP - Thrombotic thrombocytopenic purpura
Formation of vWF multimers leading to platelet aggregation (thrombosis) and thus thrombocytopenia. Can be acquired or inherited.
Plasma exchange to remove vWF multimers and Ab and provide the protease. Schistocytes (fragmented RBCs) are produced as fibrin strands (from the thrombi) shred RBCs as they try to move past the thrombus. Schistocytes seen in TTP and also DIC.
DIC – disseminated intravascular coagulation
A patient may have both thrombosis and bleeding at the same time. The thrombosis uses up lots of platelets. This causes the rest of the body to be low in platelet numbers. They are also heavily bleeding in another area. Due to the low platelet concentration in that area of the body
Treatment depends on whether bleeding (fresh frozen plasma) or thrombotic (heparin)! Treatment depends on which is the most severe and pressing the bleeding or thrombotic.
Von Willebrand disease (VWD)
- Type 1: Quantitative partial deficiency
- Type 2: Functional abnormality
- Type 3: Complete deficiency
vWF produced in endothelial cells and megakaryocytes and has 2 main roles –
– Platelet adhesion, sticks platlets to collogen
– Carries FVIII, protecting it from premature destruction.
vWF produced in endothelial cells, so technically not a platelet defect. However, results in a defect in platelet adhesion. vWF carries FVIII, so vWD will cause prolonged aPTT.
- Often requires no treatment
- Education - drug avoidance (aspirin etc), contact sport avoidance, dental hygiene, menstruation – risk of anaemia
- Local haemostatic agents
Bernard–Soulier syndrome (BSS), also called hemorrhagiparous thrombocytic dystrophy,is a rare autosomal recessive bleeding disorder that causes a deficiency of glycoprotein Ib (GpIb), the receptor for von Willebrand factor.
• Widely used anti-platelet drug.
• Irreversibly acetylates the enzyme cyclooxygenase-1 (ie acts for lifespan of platelet).
• COX catalyses TXA2 production in platelets and PGI2 production in endothelial cells (balancing act!)
• Risk of major bleed with aspirin is <1% per year
• Discontinue aspirin 7-10 days before surgery (if can).
• Treatment = platelet transfusion and DDAVP (desmopressin, induces release of vWF from endothelial cells).
Chronic renal failure
Renal failure causes # bleeding time due to either
o Uraemia (high nitrogen in blood leading to multiple platelet defects) Thrombocytopenia seen in 16-55% of patients with uraemia. Patients on dialysis have # reticulated platelets (indicating increase turn over).
o Anaemia (decrease Epo synthesis by kidneys). Seems to affect platelet – vessel wall interactions
o RBC packs (bulk blood, pushing platelets to the vessel walls)
o Platelet transfusions (limited effect as then in uraemic plasma)
Platelet activation and degranulation occurs in the extracorporeal circuit (out of the body). 2000 cardiopulmonary bypasses performed every 24 hours. Excessive bleeding is uncommon. Treatment is through platelet transfusion.
Several blood diseases impair platelet function eg. Most of the leukaemias / myelomas (bone marrow activity affected).
Reduced coagulation tends to arise from
- A deficiency in a coagulation factor
- Abnormalities of fibrinogen
c/w thrombophilia (venous thrombosis) which tends to arise from a deficiency in coagulation inhibitors
Coagulation factor deficiencies
• DIC - wide spread inappropriate intravascular deposition of fibrin with consumption of coagulation factors and platelets
• Liver Disease
• Vitamin K deficiency
• Acquired haemophilia
– Generally autoantibody against FVIII.
• Idiopathic or associated with other autoimmune diseases
• Drug treatment eg. Penicillin.
Abnormalities of fibrinogen
• Quantitative deficiencies
• Autosomal recessive. Severe symptoms.
• Less defined. Milder symptoms.
• Qualitative deficiencies
– Dysfibrinogenaemia - Autosomal dominant. May have haemorrhagic (50%) or thrombotic effect (10%)!
- The gene for FVIII is at the tip of the X-chromosome.
- DDAVP (1-amino 8-D-arginine vasopressin) mobilises stores of vWF and FVIII.
- Use of gene therapy being explored to cure Haemophilia A.