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Old 05-10-2015
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Default Pt, ptt, inr

can anyone plz explain the difference between these values. i know that PTT is for the intrinsic pathway and PT is for the extrinsic pathway but i don't understand what exactly they mean or what they are measuring.
thanks
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Quote:
Originally Posted by Hohepa
Prolonged PT is seen in factor VII deficiency, Vitamin K deficiency, Warfarin therapy, Liver disease, and Factor VII inhibitors.

Prolonged PTT is seen in von Willbrand, hemophilia A and B and C, Heparin therapy, and Antiphospholipid syndrome

Prolonged PT and PTT is seen in deficiencies of the final common pathway factors such as factor V, prothrombin, fibrinogen, or factor X. Also in Liver disease, DIC, and combined heparin and warfarin therapy.
We do this tests to measure any alteration in the timings of this tests any increase in timing will suggest pathology,I have listed the pathologies above with prolonging of PT,PTT...

When you say PTT is for the intrinsic pathway, it means that deficiency of any of the factors of the intrinsic pathway will lead to an increased PTT(XII,XI,IX,VIII) also since the Heparin acts on the activated forms of the factors (IIa,Xa,IXa,XIa,XIIa) so heparin therapy will increase PTT more than it will increase PT(VII mainly).

When you say PT is for the extrinsic pathway, it means that deficiency of any of the factors of the extrinsic pathway will lead to an increased PT(VII) also since the Warfarin acts on the factors (II,VII,IX,X) so warfarin therapy will increase PT(VII) more than it will increase PTT(XII,XI,IX,VIII mainly).


Coming to INR is International normalized ratio,

Quote:
Originally Posted by Wikipedia
The result (in seconds) for a prothrombin time performed on a normal individual will vary according to the type of analytical system employed. This is due to the variations between different batches of manufacturer's tissue factor used in the reagent to perform the test. The INR was devised to standardize the results. Each manufacturer assigns an ISI value (International Sensitivity Index) for any tissue factor they manufacture. The ISI value indicates how a particular batch of tissue factor compares to an international reference tissue factor. The ISI is usually between 1.0 and 2.0. The INR is the ratio of a patient's prothrombin time to a normal (control) sample, raised to the power of the ISI value for the analytical system being used.



INR is basically a ratio and a more standardized form of PT and the normal range for a healthy person not using warfarin is 0.81.2, and for people on warfarin therapy an INR of 2.03.0 is usually targeted.

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Old 05-11-2015
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thanks for the great explaination!!!
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Old 05-11-2015
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Quote:
Originally Posted by sm3356 View Post
can anyone plz explain the difference between these values. i know that PTT is for the intrinsic pathway and PT is for the extrinsic pathway but i don't understand what exactly they mean or what they are measuring.
thanks
These are good things to understand, both for step exams and clinical practice. I find it helpful to understand what they actually do in the lab to obtain each number because it dovetails with how they're interpreted.

PT: Take plasma, lab adds tissue factor, measures how long it takes to clot. Since we're starting with TF, we're measuring the extrinsic pathway.

INR: Each lab will report a ratio comparing the patient's PT to a reference standard on their equipment and using their batch of TF. This helps eliminate some of the natural variation seen in the PT itself.

PTT: similar method to the above, but now we add phospholipid and an activator to stimulate the intrinsic pathway. This method also explains why we see prolonged pTT with lupus anticoagulant!
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@young doc
thanks!! that really cleared it up, makes so much more sense now
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