LO4

What is the principle of prothrombin time

screening for extrinsic and common pathways

Which factros are being tested for in PT

VII, X, V, II, I

What factor is PT most sensitive to? What is it moderately sensitive to?

VII - V and X - sensitive to severe prothrombin and fibrinogen deficiences

What specimen is collected for PT

Na Citrate for Platelet poor plasma

What is in the reagent for PT testing

phospholipid from tissue source with protein and added CaCl2

What is the control

commercial is lyphozed or frozen - normal and abnormal

WHat is important with a reconstituted vial of reagent or control

Cleary mark the vial with date/time reconstituted, expiry, and initials

What is the procedure of running a PT

add plasma to cuvetter and warm to 37 degrees - add reagent to plasma timer starts - timer shuts off when clot is detected

What is the saskpolytech criteria for PT

performed in duplicate for semi-automated testing - duplicate tests must be within 0.5 seconds - of prolonged value greater than 30 seconds

How is prothrombin reported

seconds or international normalized ratio

What is the International Normalized Ratio

reagent and instrument differences are standardized - uses international sensitivity index - ISI is supplied by reagent manufacturer and each instrument will have a specific number

What is the formula for INR

(Patient PT/geometric mean of the reference range)^ISI - recorded to 1 decimal place

WHat is the reference range for PT

11.5-14.5 seconds - 0.8-1.2 INR

What is the critical INR value

>4.0

What are causes of shortened PT

abnormal high levels of any of the factors - may indicate thrombophilia (a hypercoagulable state)

What are causes of Prolonged PT

Factor deficiency - liver disease (factors not being produced) - Bowel Obstruction/lack of Vitamin K absorption (II, VII, IX, X) - Vitamin K Antagonist therapy (warfarin) - disseminated intervascular coagulation (DIC)

What is warfarin therapy

vitamin K antagonist used for long term anticoagulant therapy - interferes with the action of Vitamin K on the dependent factors - no direct effect on clot lysis

How can you reverse Warfarin therapy

Giving the patient vitamin K (will do it in 6-24 hours) or FFP (immediate)

What conditions use Warfarin as treatment

Treatment of Venous Thrombosis, Treatment of Pulmonary Embolism, Prevention of systemic embolism and recurrent systemic embolism, acute myocardial infarction, Mechanical prosthetic valves, tissue heart valves

What is the benefit of using PT to monitor Warfarin therapy

simple, reproducible, convenient, inexpensive - 3/5 factors measured by PT are sensitive to Vit K antagonist - Factor VI is most sensitive - INR standardized testing

WHat is INR only significant for when monitoring warfarin therapy

oral anticoagulants

When do we not report INR

Liver Disease, Factor deficiencies, Vitamin K deficiency

What are the interferences of PT

Drugs (can enhance bleeding or depress reoccurrence of thrombosis) - Food

What are the effects of illness on oral anticoagulant therapy

illnesses may affect PT results of patients on oral anticoagulants - Dietary can increase Vitamin K resulting in shortened PT - Examine previous results of patients on established anticoagulant therapy