Bleeding Disorders

Bleeding defects

Bleeding defects may result from:

       vascular defects (weak vessels – leak)

       decreased platelet number (thrombocytopenia)cau

       decreased platelet function

       decreased coagulation

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Thrombocytopenia

·       Normal platelet count = 150 – 400 x 109/L

·       Thrombocytopenia: Blood platelet count of <150 x 109/L

Causes:

  • Failure of marrow production
  • Shortened lifespan
  • Sequestration
  • Dilution by massive blood transfusion
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Idiopathic thrombocytopenic purpura

Idiopathic = unknown cause

Thrombocytopenic = low platelet count

Purpura = 3mm-1cm purple blemishes indicative of bleeding under the skin

Acute

  • 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

Chronic

  • 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.

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ITP Treatment

Acute:

      Often just observation as it normal goes away within 6 weeks

Chronic:

      Corticosteroids

      Splenectomy ( spleen removal)

      High dose intravenous immunoglobulin therapy

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TTP - Thrombotic thrombocytopenic purpura

Formation of vWF multimers leading to platelet aggregation (thrombosis) and thus thrombocytopenia. Can be acquired or inherited. 

Treatment 

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.

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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. 

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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 
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Bernard-Soulier Syndrome

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. 

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Aspirin

       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).

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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

Treatment: 

o   RBC packs (bulk blood, pushing platelets to the vessel walls)

o   Platelet transfusions (limited effect as then in uraemic plasma)

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Cardiopulmonary bypass

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.

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Haematological diseases

Several blood diseases impair platelet function eg. Most of the leukaemias / myelomas (bone marrow activity affected).

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Coagulation

Reduced coagulation tends to arise from

  •  A deficiency in a coagulation factor
  •  Inherited
  •  Acquired
  • Abnormalities of fibrinogen

c/w thrombophilia (venous thrombosis) which tends to arise from a deficiency in coagulation inhibitors

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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

       Malignancy

       Pregnancy

       Drug treatment eg. Penicillin.

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Abnormalities of fibrinogen

       Quantitative deficiencies

      Apofibrinogenaemia

       Autosomal recessive.  Severe symptoms.

      Hypofibrinogenaemia

       Less defined.  Milder symptoms.

       Qualitative deficiencies

      Dysfibrinogenaemia -   Autosomal dominant.  May have haemorrhagic (50%) or thrombotic effect (10%)!

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Haemophilia

-          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.

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