NBME 18 -Hematology Q - confusing

[zeevee]

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50 year old man is admitted to the hospital after being diagnosed with pulmonary embolus .Treatment is started with IV heparin .24 hrs later warfarin is added .On day 2 his PTT is 52 seconds ( control 26 secs) , PT is 12 s ( control 12 sec) and INR is 1.0 .What is the best explanation for normal Pt and INR measurements in this patient ?
a) Heparin warfarin interaction
b) Hereditary resistance to warfarin
c) Hereditary resistance to heparin
d) Long half life of factor II prothrombin
e) Too low a dose of heparin
f) Too low a dose of warfarin
g) Undetected liver disease

 

[dfib slim]

50 year old man is admitted to the hospital after being diagnosed with pulmonary embolus .Treatment is started with IV heparin .24 hrs later warfarin is added .On day 2 his PTT is 52 seconds ( control 26 secs) , PT is 12 s ( control 12 sec) and INR is 1.0 .What is the best explanation for normal Pt and INR measurements in this patient ?
a) Heparin warfarin interaction
b) Hereditary resistance to warfarin
c) Hereditary resistance to heparin
d) Long half life of factor II prothrombin
e) Too low a dose of heparin
f) Too low a dose of warfarin
g) Undetected liver disease

Should be D. Not enough time has passed for warfarin's effects to kick in and takes 2-3 days to see an effect. This patient's labs were only after one day.

 

[daktarsahab]

heparin bridging was done so it shouldnt take that long no ?

 

[danceplaylove]

edit - nevermind!

 

[zhopv10]

This question bugs me because the PT should start dropping within 7ish hrs (something like the half life of factor VII can't remember the exact number). The EFFECTS of the warfarin won't really be working until a day or two later due to the long half life of factor II but that won't be reflected on the PT (this is a common phenomenon). I tried looking this up after taking 18 and just Couldn't find any reason to support factor two half life leading to the PT not changing. Whats more it should be decreased anyway from the heparin bridge... I put warfarin dose too low which I feel like is totally valid and happens all the time in practice (hence why they have to get blood tests and adjust dosage a bit at first it's fairly volatile). Oh well, rant over lol


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