Platelets, and Coagulation System

Fadel Muhammad Garishah, BSc

Thrombosis and Virchow’s Triad

Platelets • Megakaryocytes’ daughters

• Actors of primary thrombosis

• Activated and inhibited by various stimuli

• Also involved in both hemostatic and immunity-inflammation processes

Endothelial cells

• Lining of the vascular system• Possessed various adhesion molecules for the adhesion of platelets, WBCs during

thrombosis and inflammation processes

Hemostasis – Thrombosis - Fibrinolysis

http://www.hopkinsmedicine.org/hematology/coagulation.swf

Platelet Activation

Coagulation Cascade and Fibrin Polymerization

Fibrinolysis

Clinical Evaluation of Thrombosis• Clotting Time• Bleeding Time• Prothrombin Time• Activated Partial Thromboplastin Time

Bleeding time• Platelet functions to form clot• Wound in superficial area -> normally 1-9 min stops• Prolonged: platelet dysfunction, vWD, anticoagulant use,

uremia, liver failure, leukemias, MDS

Thrombin time• Assess fibrin formation in plasma• TT time < 20 seconds• Shortened: hereditary, DIC, multple myeloma

Prothrombin Time• Extrinsic factors and final common pathway• Factor II, V, VII, X• Adding Ca2+ and thromboplastin (activator) to blood sample,

and then measure the time• PT 9,5 – 13,5 seconds• INR < 1.• Prolonged PT: warfarin use, def vit K, liver disease, deficiency

of F II, VIII, V, X, DIC, fibrinogen abnormalities, heparinization

Partial Thromboplastin Time or Activated Partial Thromboplastin Time

• Intrinsic coltting factors etc• aPTT additional activator that speeds up PTT• aPTT 30-40 seconds• PTT 60 – 70 seconds• Prolonged causes: Def F VIII, IX, XI, XII,

Fitzgeralnd/prekalikrein, vWD, hypofibrinogenemia, liver cirrhosis, def vit K, , DIC, heparinization, coumarin inhibition FI, IX and X

• Shortened: early DIC, cancers, hemorrhage,