Heparin and PROTHROMBIN time

[Phloston]

UWorld has a chart in one of its explanations where it shows, for heparin: normal PT, increased aPTT, normal PC, normal BT.

In the very same chart, for warfarin, it says: increased PT, increased (delayed) PTT, normal PC, normal BT.

This confuses me because, if they go out of their way to show increased aPTT for warfarin, why wouldn't they also go out of their way to show increased PT for heparin?

The reason I bring this up is because if we were to encounter a simple arrows-question on the real USMLE, the arrows should be up for PT and aPTT for both heparin and warfarin, despite the fact that the former is monitored via aPTT and the latter via PT. So the reason UWorld doesn't do that here is beyond me.

Any thoughts?

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[withrye]

It just happens that the difference in PTT vs PT elevation in heparin is much higher than the reverse difference for warfarin. That is to say, you need pretty big doses of heparin to see a meaningful rise in PT. You don't need huge doses of warfarin to see a rise in PTT. I think almost any presentation of heparin wrt PT and PTT will show a normal PT and increased PTT. The reverse is not true of warfarin therapy (you might see elevated PT and PTT, although PT (INR) is the preferred tracking metric).

 

[OveractiveBrain]

UWorld has a chart in one of its explanations where it shows, for heparin: normal PT, increased aPTT, normal PC, normal BT.

In the very same chart, for warfarin, it says: increased PT, increased (delayed) PTT, normal PC, normal BT.

This confuses me because, if they go out of their way to show increased aPTT for warfarin, why wouldn't they also go out of their way to show increased PT for heparin?

The reason I bring this up is because if we were to encounter a simple arrows-question on the real USMLE, the arrows should be up for PT and aPTT for both heparin and warfarin, despite the fact that the former is monitored via aPTT and the latter via PT. So the reason UWorld doesn't do that here is beyond me.

Any thoughts?

Because in practice you follow PT for coumadin (standardized between labs by the INR) and PTT for heparin. Of course both will cause elevations in both, because both effect the common pathway. Getting you set up for life, bra.