Ans. (a) aPTTRef: Robbins and Cotran Pathologic Basic Disease 9th Ed; Page No-119* The extrinsic pathway is clinically evaluated by the prothrombin time (PT), which is a measure of factors II, V, VII, X, and fibrinogen.Diatheses* The intrinsic pathway can be evaluated by the partial thromboplastin time (PTT), which is a measure of factors II, V, VIII, IX, X, XI, XII, and fibrinogen.Coagulation cascadeIntrinsic pathwayExtrinsic pathway* Mainly in vitro pathway of coagulation but it may be activated in vivo also.* This pathway may involve contact activation with interactions of the so- called contact factors: factor XII (Hageman factor), prekallikrein, and high- molecular weight kininogen, as well as factor XI.* In vivo activation occurs due to contact activation of factor XII from subendothelial collagen and other components like platelets following endothelial injury.* It is probably initiated by the tissue factor-factor Vila complex (from the extrinsic pathway), activating factor IX to factor IXa. Factor IXa, in turn, leads to the conversion of factor X to factor Xa, catalyzed by factor Villa.* It is mainly in vivo pathway but it may be activated in vitro also.* In vivo it is initiated by tissue factor, which activates factor VII and forms a Vila tissue factor complex.* The Vila tissue factor complex initiates coagulation through the activation of factor X to factor Xa (and additionally factor IX to factor IXa).* Factor Xa converts prothrombin (factor II) to thrombin (factor lla).* In the conversion of prothrombin to thrombin factor-Va acts as a cofactor.* In vitro activation occurs due to exposure of blood to tissue derived thromboplastin reagents (tissue factor).Extra MileLaboratory Assessment of Coagulation Pathways* Prothrombin time (PT):* Normal range is 11-16 seconds.* Used for assessment of extrinsic and the common coagulation pathways.* It is prolonged by:o Deficiency of VII, X, V, prothrombin (II) and Fibrinogen (I).o Warfarin treatment* Activated Partial Thromboplastin Time (aPTT):# Normal range is 30-40 seconds# Used for intrinsic and the common coagulation pathways.# It is prolonged by:o Deficiency of XII, XI, IX, III, X, V, prothrombin (II) and Fibrinogen (I).o Heparin treatment* Thrombin Time (TT):# Normal range is 11-14 seconds# Use for assessment of conversion fibrinogen into fibrin.# It depends upon adequate fibrinogen levels.# It is elevated in dysfibrino genemia, afibrinio genemia, DIC and heparin like inhibitors.