1. Dr. S. Parthasarathy MD DA DNB PhD (physio) Mahatma Gandhi medical college and research institute, puducherry – India Prothrombin time

2. Coagulation factors I (fibrinogen) Forms clot (fibrin)fibrinogen II (prothrombin)prothrombin III) Calcium IIICalcium phospholipid (formerly known as factor IV) V (proaccelerin, labile factor V VI Unassigned – old name of Factor Va VI VII (stable factor, proconvertin) VII VIII (Antihemophilic factor A) VIII IX (Antihemophilic factor B or Christmas factor) IX X (Stuart-Prower factor) X XI (plasma thromboplastin antecedent)XI XII (Hageman factor) XII XIII (fibrin-stabilizing factor) Crosslinks fibrin XIII

3. INITIATION OF BLOOD COAGULATION Extrinsic Pathway Tissue trauma Tissue trauma Leakage of Tissue Factor Leakage of Tissue Factor XXa 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 XXa Ca + 2 Prothrombin activator activator Prothrombin Thrombin (factor II) Thrombin converts fibrinogen to fibrin

4. 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

5. Normal value 11- 14 seconds What is INR?

6. 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

7. INR = [PT pt ] ISI [PT Ref ] [PT Ref ] PT pt – prothrombin time of patient PT Ref – prothrombin time of normal pooled sample ISI – International Sensitivity Index

8. 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

9. Example Patient PT = 16 sec. Control = 12 seconds. 16/12 = 1.33. But if ISI is 2 INR = (1.33) 2 = 1.768.

10. Prothrombin time Factor 7 It is also prolonged in 1,2,5,10 But not useful for factor 8 and 9

11. importance of Prothrombin time Liver disease Warfarin therapy Vit. K deficiency

12. Factors raise INR Chr. Alcohol Anabolic steroids Septran Propranolol Metrogyl Fluroquinolones. INH,omez

13. Factors decrease INR Barbiturates Carbamazipine. Griseofulvin Sucralfate. Rifampicin.

14. Thank you all!!