Warfarin and lab values

[Qester]

Hello,

What effect does warfarin have on lab values (PT, aPTT)?

I had assumed since it disrupted vitamin K clotting factors (2, 7, 9, 10) you would see an increase in both PT and PTT, and that we monitored PT for more sensitivity since factor 7 is the first factor to decrease.

However I just had a question stating that at appropriate doses ONLY PT is increased, as only factor 7 is inhibited, and its not until high doses of warfarin do the other factors get implicated.

Any insight is appreciated.

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[Doc-Res]

Thats true because factor VII is the coagulation factor with shortest half life. That would explain why PTT is only affected when greater doses are administered.

 

[RK.md]

Yeah, for testing purposes, PT is a surrogate for warfarin activity. Pts on high doses of warfarin will also have a bump in their PTT over time, but as mentioned, factor 7 is the first to be affected due to its short half-life and therefore PT is the first to change.