dr. s. parthasarathy md da dnb phd (physio) mahatma gandhi medical college and research institute,...
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Dr. S. Parthasarathy MD DA DNB
PhD (physio)Mahatma Gandhi medical
college and research institute , puducherry – India
Prothrombin time
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Coagulation factors• I (fibrinogen) Forms clot (fibrin) • II (prothrombin) • III) Calcium • phospholipid (formerly known as factor IV) • V (proaccelerin, labile factor• VI Unassigned – old name of Factor Va • VII (stable factor, proconvertin) • VIII (Antihemophilic factor A) • IX (Antihemophilic factor B or Christmas factor) • X (Stuart-Prower factor) • XI (plasma thromboplastin antecedent) • XII (Hageman factor) • XIII (fibrin-stabilizing factor) Crosslinks fibrin
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INITIATION OF BLOOD COAGULATION
Extrinsic Pathway
Tissue trauma
Leakage of Tissue Factor
X Xa
Prothrombin activator
Ca+2, factor VII
Ca+2
Prothrombin Thrombin(factor II)
Ca+2
Intrinsic Pathway
Blood trauma/ contact with collagen
Activation of factor XII, IX, VIII
X Xa
Ca+2
Prothrombin activator
Prothrombin Thrombin(factor II)
Thrombin converts fibrinogen to fibrin
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Prothrombin time tests extrinsic pathway
• Performed by adding a mixture of calcium and thromboplastin to citrated plasma
• As a control, a normal blood sample is tested continuously
• PT ratio (PTR) = Patient’s PT Control PT
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Normal value
• 11- 14 seconds
• What is INR?
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• Thromboplastins are extracts from brain, lung or placenta of animals
• Thromboplastins from various manufacturers differ in their sensitivity to prolong PT
• May result in erratic control of anticoagulant therapy
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INR = [PTpt] ISI
[PTRef]
PTpt – prothrombin time of patient
PTRef – prothrombin time of normal pooled sample
ISI – International Sensitivity Index
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ISI – International Sensitivity Index
• Thromboplastin may vary.• Each manufacturer gives ISI value• With reference to international
control.• If the manufacturer gives 1 , it
means ,the sensitivity is same• If 2, batch is half sensitive.• Usually between 1 to 1.4
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Example
• Patient PT = 16 sec.• Control = 12 seconds.• 16/12 = 1.33.
• But if ISI is 2 • INR = (1.33)2
• = 1.768.
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Prothrombin time
• Factor 7
• It is also prolonged in 1,2,5,10
• But not useful for factor 8 and 9
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importance of Prothrombin time
• Liver disease• Warfarin therapy• Vit. K deficiency
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Factors raise INR
• Chr. Alcohol• Anabolic steroids• Septran• Propranolol• Metrogyl• Fluroquinolones.• INH,omez
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Factors decrease INR
• Barbiturates• Carbamazipine.• Griseofulvin• Sucralfate.• Rifampicin.
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• Thank you all!!