So I had an interesting case today where I got called from lab with a critical PTT (>200) but the anti-xa, which we use to monitor heparin gtts, was therapeutic. My understanding is anti-xa measures more the levels of heparin in the blood and PTT is a marker of anticoagulation levels of the blood, and some institutions use PTT and some use anti-xa. PTT, or preferably aPTT, makes more sense to me, but some of what I'm reading suggests the results can be misleading. I guess my questions are these:1) What lab test is used at your facility?2) Would you feel comfortable continuing a heparin gtt on a pt with a critical PTT? Assume no major signs of bleeding and VSS otherwise.