PROTHROMBIN TIME.pptx

Basics of PT

1. COAGULATION PATHWAY

2. Prothrombin time (PT) and partial thromboplastin time (PTT) are tests used to evaluate coagulation, or the clotting of blood. The PT test, also known as the PT/INR test, looks at the  extrinsic pathway   of coagulation. The PTT test looks at the  intrinsic pathway   of coagulation.

3. The prothrombin time (PT) test measures how long it takes for a blood clot to form based on a protein produced by the liver called prothrombin . Prothrombin, also known as clotting factor 2, is one of 13 substances known as "clotting factors" that are involved in coagulation.

4. PT is a blood test that measures how long it takes blood to clot. It can be used to check for bleeding problems.

5. Once blood is drawn, a substance called tissue factor is added to the test tube. Tissue factor, also known as clotting factor 3, activates the sample in a way that illustrates how blood would clot if there is bleeding (the extrinsic pathway ). Once activated, the PT test is measured in seconds. The time is then compared to the reference range of values.

6. A number higher than the reference range means your blood is taking longer than usual to clot. A number lower than the reference range means that your blood is clotting faster than normal.

7. Clotting Too Quickly High Vitamin K intake Estrogen -containing drugs Deep vein thrombosis Pulmonary embolism Clotting Too Slowly Vitamin K deficiency Anticoagulant therapy Liver disease Hemophilia Von Willebrand disease Sickle cell disease

8. The PT test does not require fasting but foods high in vitamin K can skew the results, including beef or pork liver, green tea, dark green vegetables, or soybeans .

9. The PT test is sometimes referred to as PT/INR test. The INR refers to the international normalized ratio, a calculation that help to ensure the test results are standardized from one lab to the next.

10. INR values are important because they help to determine how well a person is responding to warfarin, one of the most commonly prescribed anticoagulants used to prevent blood clots. For people on warfarin, the reference range of values for PT/INR is 2 to 3 seconds .

11. High and low INR values are interpreted as follows: Low INR values mean that you may be at risk of dangerous blood clots . High INR values mean that you may be at risk of dangerous bleeding.

12. METHODS : Quick (One stage) method Automated method

13. QUICK (ONE STAGE) METHOD : Introduced by Dr Armand Quick in 1935. It is the time required for clotting of citrated plasma after addition of calcium and tissue thromboplastin .

14. REAGENTS & REQUIREMENTS : Thromboplastin – Cacl2 mixture reagent Control plasma Test tubes Stop watch Centrifuge Micropipette Micropipette tips 3.2% sodium citrate anticoagulated blood sample Water bath 37deg C

15. PRINCIPLE : The calcium in whole blood is bound by sodium citrate thus preventing coagulation. Tissue thromboplastin to which calcium has been added is mixed with the plasma and the clotting time is noted.

16. SPECIMEN COLLECTION & STORAGE : Collected by veinpuncture using vacutainer & mix the sample. Centrifuge at 2500-3000 rpm for 15 minutes.

17. REJECTION CRITERIA : Haemolysed sample Clotted sample Inadequate sample

18. QUICK METHOD ( MANUAL) Centrifuge the blood sample at 2500-3000 RPM for 15 minutes. Separate the plasma from the cells as soon as possible. Label two test tubes as Test tube No. 1 & 2. Add 0.1ml of patient plasma to each. Label another test tube as control.

19. Add control plasma 0.1ml. Incubates at 37deg C for 1 minute. Add 0.2ml of prewarmed thromboplastin reagent into the tube. Start the stop watch. Mix the tube & shake it in water bath for 5-6 sec. Take out the test tube & observe for clot formation against light.

20. NORMAL RANGE : 11-14 Sec. Critical value for urgent clinical notification : > 60seconds.

21. Inr – International Normalized Ratio: Introduced by WHO in 1983. PT results of different labs using different thromboplastin reagent may lead to different results even when plasma warfarin concentration is same, so leads to misinterpretation. Hence all Thromboplastin reagents distributed are caliberated against WHO reference preparation. The caliberation no is called International sensitivity index.

22. Indications for obtaining PT are: Monitoring vitamin K-antagonists (VKA) such as warfarin is the most common indication for PT. Evaluation of unexplained bleeding. Diagnosing disseminated intravascular coagulation (DIC ). Obtaining baseline value before initiating anticoagulation therapy. Assessment of liver synthesis function and to calculate the model for end-stage liver diseases (MELD) score in liver disease.

23. INCREASED PT : DIC Liver diseases Vitamin K deficiency Oral anticoagulant therapy FV, FVII, FX deficiency

24. CAUSES FOR A PROLONGED PT INCLUDE: Liver disease Liver disease or liver dysfunction leads to a decreased production of most coagulation factors. It leads to prolonged PT and physical manifestations that can include petechiae and easy bruising.

25. Vitamin K deficiency Vitamin K is a necessary component in factors II, VII, IX, and X. A deficiency in vitamin K will lead to a decrease in these factors and prolong PT. Potential causes that can lead to decreased vitamin K levels include malnutrition, prolonged antibiotic use, and impairments with fat absorption.

26. Factor deficiency Inherited diseases that lead to a decreased production of factors II, V, IX, and X will lead to a prolonged PT. Disseminated Intravascular Coagulation (DIC ) DIC causes a system-wide activation of coagulation, depleting available coagulation factors leading to an increase in PT.

27. Antiphospholipid antibodies Antiphospholipid antibody syndrome (APS) characteristically presents with recurrent thromboembolic events and/or pregnancy loss along with detected antiphospholipid antibodies ( APA ).  APA causes an increased conversion of prothrombin to thrombin in vivo, leading to an overall decrease in prothrombin. Low prothrombin levels can lead to an increased PT result.