Heparin gtt - anti-xa vs. PTT

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.
We use PTT on all our Heparin gtt patients. Do you use a nomogram-something that tells you how to run the gtt depending on how high or low the PTT is? Our facility says PTT; we don't even check the anti-xa.

1) PTT/aPTT2) No.While the anti-xa measures the amount of Heparin in the bloodstream, the aPTT measure's the patient's *response*, which will vary from person to person due to lots of different things such as renal insufficiency, for instance. Since it's the therapeutic response we're after, I would be more comfortable going by the aPTT.But there is much I don't know, so if there is something I'm missing, feel free to enlighten me.

We go by the Ptt at my hospital. We having a protocol that we follow. The rate is determined by the Ptt, meaning we wii decrease/increase depending upon the Ptt results. You should check your policy there, and if you still don't feel comfortable, call the doc and ask if he wants to continue

PTT is what we use to monitor.

We only use anti-Xa levels when they're unsure about enoxaparin dosing. For heparin infusions it's APTT all the way.

1. PTT2. No