Hematology Lab - 17 Prothrombin Time

p {margin: 0; padding: 0;} .ft00{font-size:13px;font-family:ArialMT;color:#000000;} .ft01{font-size:12px;font-family:ArialMT;color:#000000;} .ft02{font-size:13px;font-family:Arial;color:#000000;} .ft03{font-size:12px;font-family:SymbolMT;color:#000000;} .ft04{font-size:12px;font-family:Arial;color:#000000;} .ft05{font-size:12px;font-family:CourierNewPSMT;color:#000000;} .ft06{font-size:13px;font-family:SymbolMT;color:#000000;} .ft07{font-size:9px;font-family:ArialMT;color:#000000;} .ft08{font-size:13px;font-family:CourierNewPSMT;color:#000000;} .ft09{font-size:13px;font-family:Wingdings;color:#000000;} .ft010{font-size:13px;line-height:16px;font-family:Arial;color:#000000;} .ft011{font-size:13px;line-height:16px;font-family:ArialMT;color:#000000;} HEMATOLOGY LABORATORY PROTHROMBIN TIME OUTLINE • Prothrombin Time o Principle o Materials o PT Procedures o Reference Range & Clinical Significance LABORATORY EVALUATION OF SECONDARY HEMOSTASIS: PROTHROMBIN TIME • In blood coagulation, while the factors in the intrinsic pathway are activated, the extrinsic pathways factors are also performing their role to help in the clotting of the blood thus preventing its undue loss from the body. The evaluation by the factors involved in the extrinsic and common pathways is important because whether there is a deficiency or a higher level than the reference value, there will be a clinical implication. • Prothrombin time (PT) is the plasma clotting time obtained when an excess of thromboplastin and optimum calcium are added to citrated plasma under standardized conditions. PT is essentially a test of the extrinsic pathway of clotting and the common pathway. It detects deficiencies in factors I, II, V, VII and X. The test is widely accepted to monitor patients on anticoagulant therapy; due to the reduction in the activity of Vitamin K dependent factors as well as Protein C and Protein S. • Prolonged PT is also seen in Vitamin K deficiency, certain liver disease, specific coagulation deficiencies, DIC, some dysproteinemias and the presence of circulating anticoagulants and fibrin/ fibrinogen split products. • Sodium citrate is the preferred anticoagulant. The test should be performed within 2 hours after blood collection. PRINCIPLE • The one stage PT measures the clotting time of plasma after adding a source of tissue factor (thromboplastin) and calcium. The recalcification of plasma in the presence of tissue factor generates activated factor X, with the consequent formation of thrombin and ultimately a fibrin clot. MATERIALS • Two way needle • Citrated evacuated tube • Centrifuge • 0.1 ml serological pipette • 0.2 ml serological pipette • Wasserman tube • 37 o c water bath • Prothrombin reagent • Tissue paper • Timer PT PROCEDURES PREPARATIONS OF SPECIMEN FOR PT 1. Collect venous blood on a citrated tube. 2. Centrifuge at 1, 500 rpm for 5 minutes. 3. Separate the plasma by placing it into a clean dry tube. TEST PROCEDURE 1. Plasma/ control 0.1 ml 2. Incubate at 3-5 minutes at 37 oc 3. Add PT reagent 4. Start time with addition of reagent. Record time required for. REFERENCE RANGE & CLINICAL SIGNIFICANCE • Reference Range : 10 – 14 seconds • Clinical Significance o Values below 60% indicate a tendency to bleed. o Spontaneous bleeding occurs when the prothrombin concentration is less than 20%. o Values between 20% and 30% are desirable during heparin and dicumarol therapy. o Increase in seconds (decrease in percentage) is due to: ▪ Inability of the liver to form prothrombin from Vitamin K in severe liver damage. • The response of prothrombin time to parenteral Vitamin K therapy is not only of diagnostic but also of prognostic value in liver disease. • If the prothrombin returns to normal after Vitamin K administration, the liver is not severely damaged. ▪ Poor absorption of Vitamin K from the intestine • Chronic lesions of intestinal tract • Absence of bile in obstructive jaundice and external biliary fistula of long standing ▪ Inadequate intake of Vitamin K in deficiency anemia. ▪ Inability of newborn to manufacture Vitamin K due to lack of intestinal bacteria. ▪ Salicylate therapy ▪ Heparin and dicumarol therapy o Decrease in seconds (increase in percentage) is found in acute thromboplebitis multiple myeloma, after digitalis therapy, and after undergoing anesthesia. o A useful screening procedure for the extrinsic coagulation mechanism including the common pathways ( detects deficiencies in factor II, V, VII, X) o The PT is frequently used to follow the course of oral anticoagulant therapy •