Haemopoetic system Flashcards
Features of heparin induced thrombocytopenia include
A Type I is more dangerous than type II thrombocytopenia
B It occurs in about 5% of patients receiving heparin
C Bleeding is the main complication of the disease
D It does not occur with low molecular weight heparin
B
Explanation
Heparin induced thrombocytopenia (HIT) occurs in about 5% of patients. Most develop type I thrombocytopenia which is of little danger. Type II thrombocytopenia is less common but of much greater clinical significance. It occurs 5-14 days after heparin therapy begins. It is caused by antibodies that recognise complexes of heparin and platelet factor 4 (a normal platelet granule). Binding of heparin to these complexes results in the activation, aggregation and consumption of platelets (hence thrombocytopenia). However, this effect on platelets and endothelial damage combine to produce a prothrombotic state even in the face of heparin administration and thrombocytopenia (paradoxical). Life threatening arterial and venous thrombosis occurs. Unless heparin therapy is stopped, large clots will occur which will lead to organ and limb ischaemia (arterial side) and DVT and PE (venous side). If a patient was already exposed to heparin, the disease can occur earlier (as antibodies are already present). Low molecular weight heparin (LMWH) reduces the risk but does not remove it completely. If one developed HIT, even LMWH may exacerbate the thrombotic tendency and must be avoided
From the TB directly:
HIT is a systemic hypercoagulable state that occurs in 1-4% of individuals treated with UFH. Surgical patients are at greatest risk. The reported incidence of HIT is lower in paediatric populations outside the critical care setting; it is relatively rare in pregnant women. The risk of HIT may be higher in individuals treated with UFH of bovine origin compared with porcine heparin and is lower in those treated exclusively with LMW heparin.
Morbidity and mortality in HIT are related to thrombotic events. Venous thrombosis occurs most commonly , but occlusion of peripheral or central arteries is not infrequent. If an indwelling catheter is present, the risk of thrombosis is increased in that extremity. Skin necrosis has been described, particularly in individuals treated with warfarin in the absence of a direct thrombin inhibitor, presumably due to acute depletion of vitamin K dependent anticoagulation protein C occurring in the presence of high levels of procoagulant proteins and an active hypercoagulable state. The following points should be considered in al patients receiving heparin. Platelet counts should be performed frequently; thrombocytopaenia appearing in a time frame consistent with an immune response to heparin should be considered suspicious for HIT; and any new thrombus occurring in patients receiving heparin should raise suspicion of HIT. Patients who develop HIT are treated by discontinuance of heparin and administration of the direct thrombin inhibitor argatroban.
Which of the following is true regarding Haemophilia A?
A The extrinsic pathway is unaffected
B It is an inherited disease only
C Bleeding occurs in males only
D All forms of the disease produce severe bleeding
A
Explanation
Haemophilia A is the most common inherited disease associated with life threatening bleeding. Note, however, that 30% of patients do not inherit the disease but it is caused by new mutations in factor VIII. It is X linked inherited, so bleeding occurs in males and homozygous females. Patients with 6-50% of normal factor have a mild form of the disease. Although the extrinsic pathway is intact, it is insufficient to provide a stable clot and stop bleeding. The intrinsic pathway is required for the formation of a stable clot and this is deficient in Haemophilia. The PT is normal and the PTT is raised.
Which of the following is a non-ideal effect of Heparin?
A Heparin induces a thrombocytosis
B Heparin induces antibodies against red blood cells
C Heparin induces a prothrombotic state
D Heparin induces the antiphospholipid syndrome
C
Explanation
Antiphospholipid syndrome (APS), although similar in pathogenesis to heparin-induced thrombocytopaenia (HIT), heparin does not induce APS. The mainstay of treatment is heparin followed by warfarin. Heparin induces antibodies against platelets and endothelium (HIT). Heparin induces a thrombocytopenia (HIT). During HIT- this effect on platelets and endothelial damage combine to produce a prothrombotic state even in the face of heparin administration and thrombocytopenia (paradoxical)-see below
Note:
Up to 8% of patients receiving heparin are at risk to develop HIT antibodies,but only 1–5% on heparin will progress to develop HIT with thrombocytopeniaand subsequently one third of them may suffer from arterial and/or venous thrombosis.
Source: heparin induced thrombocytopenia: ncbi.nim.nih.gov>articles> PMC2600013
Extensive explanations:
Antiphospholipid syndrome (APS) and heparin-induced thrombocytopenia (HIT) are immune-mediated thrombotic conditions caused by antibodies targeted to a protein-antigen complex. Although each disorder is attributed to two distinct antibodies, these autoimmune disorders are characterized by a similar pathogenesis that includes a hypercoagulable state, platelet activation, damage to the vascular endothelium, and inflammation. APS and HIT share similarities in the clinical presentation because each is associated with thrombocytopenia, a high risk of thrombosis in all venous and arterial sites, and catastrophic thrombotic outcomes occur if untreated
Heparin induced thrombocytopenia (HIT) occurs in about 5% of patients. Most develop type I thrombocytopenia which is of little danger. Type II thrombocytopenia is less common but of much greater clinical significance. It occurs 5-14 days after heparin therapy begins. It is caused by antibodies that recognise complexes of heparin and platelet factor 4 (a normal platelet granule). Binding of heparin to these complexes results in the activation, aggregation and consumption of platelets (hence thrombocytopenia). However, this effect on platelets and endothelial damage combine to produce a prothrombotic state even in the face of heparin administration and thrombocytopenia (paradoxical). Life threatening arterial and venous throbosis occurs. Unless heparin therapy is stopped, large clots will occur which will lead to organ and limb ischaemia (arterial side) and DVT and PE (venous side). If a patient was already exposed to heparin, the disease can occur earlier (as antibodies are already present). Low molecular weight heparin (LMWH) reduces the risk but does not remove it completely. If one developed HIT, even LMWH may exacerbate the thrombotic tendency and must be avoided
Which of the following laboratory findings in Immune thrombocytopaenic purpura is false?
A Increased megakaryocytes
B Elevated PTT
C IgG autoantibodies
D Large platelets in the peripheral smear
B
Explanation
Blood workup- thrombocytopaenia, normal to increased megakaryocytes in the bone marrow, large platelets in the peripheral smear, PT normal, PTT normal. Autoantibody testing is not widely available, but is of the IgG class. The diagnosis however, is one of exclusion.
Which is the most common inherited bleeding disorder in humans?
A Haemophilia A
B Haemophilia B
C Congenital prothrombin deficiency
D Von Willebrand disease
D
Explanation
Von Willebrand disease is the most common inherited bleeding disorder in humans. Affecting about 1% of adults in the USA. Most of the time, the bleeding disorder is mild and goes unnoticed until a haemoststic stress, such a surgery or stress reveals its presence. Transmitted as an autosomal dominant disorder, but rare autosomal recessive variants have been discovered. Most often presents as bleeding form gums, menorrhagia. Lab tests show a prolonged bleeding time in the presence of a normal platelet count. There are 3 types. Type 1 and 3 are associated with a decreased vWF and type 2 has defective vWF.
25-year-old man of Middle Eastern descent presents with a mild hypochromic, microcytic anaemia. Which of the following conditions most likely explains his blood results?
A B12 deficiency
B Sickle cell disease
C Beta-thalassaemia minor
D Anaemia of chronic disease
C
Explanation
Beta-thalassaemia minor causes a mild hypochromic, microcytic anaemia. It is usually an asymptomatic condition but recognition of the trait is important for genetic counselling.
Sickle cell disease causes a chronic haemolytic anaemia with microvascular occlusion.
B12 deficiency causes a megaloblastic anaemia, with abnormally large and oval red blood cells in peripheral blood.
Anaemia of chronic disease usually causes a normochromic, normocytic anaemia, but can also produce a hypochromic, microcytic anaemia.
A patient with A+ blood type accidentally receives a transfusion of B+ blood. Which of the following best describes the antibody response produced?
A The patient will produce anti-B antibodies to A antigens of the donor blood
B The patient will produce anti-A antibodies to B antigens of the donor blood
C The patient will produce anti-A antibodies to A antigens of the donor blood
D The patient will produce anti-B antibodies to B antigens of the donor blood
D
