Today while rounding, our attending asked a seemingly innocuous question, “What are the vitamin K dependent clotting factors?” Among the barrage of knee jerk responses the intern had clearly gotten his words out first, “Two, Seven, Nine and Ten.” The attending’s response, “No.” The look on that intern’s face was priceless. It had a mix of utter disbelief, shock, and even some anger in there. “What do you mean, No?” The intern asked. “I mean, No.” The attending was thoroughly enjoying this. After a palpable pause, a friend of mine (the other med student) ended up saving the day with two more syllables, “C, S.” The attending was pleased.
HEPARIN AND WARFARIN
We ended up spending the next few minutes discussing why it is so important to consider these other two proteins in our knee jerk response. If a patient needs to be anti-coagulated for any acute venous thromboemboli you should treat with heparin AND warfarin. Warfarin inhibits vitamin K dependent carboxylation of the factors mentioned above, and because Proteins C and S have anticoagulating properties and have relatively shorter half lives, they get affected by Warfarin first and create a temporary PROTHROMBOTIC state. The heparin given for the first 5-6 days of the treatment is to cover that brief window where Proteins C and S are out of commission, at least until the INR is therapeutic (2.0-3.0).
Interestingly enough, I found out that there is another anticoagulant that is Vitamin K dependent, Protein Z. It seems it works on inhibiting Xa…good to know. If this was all boring repetition for you then great, thats kind of the point. I thought I’d put this up here because I was surprised at how many had forgotten exactly the roles of Proteins C and S.
And here’s our lovely cascade for your reviewing pleasure: