venipuncture or portable machine?

I have been looking for a definite answer for this one but having no luck! I would like to know how long do we wait to do a fingerstick INR via portable unit to test a patient's level after the last dose of an injectable Blood thinner(lovenox, arixtra,etc)? We do not use the portable units while patients' are on injectables but wonders how long we should wait to use the portable units and get ACCURATe results.
Thanks!
I'm not familiar with these machines, but INR is for Coumadin.

Well, when we have patients on Coumadin, we use the portable machines to check their INR levels. But when they are on injectable blood thinners then we do venipuncture to check serum PT/INR levels. I would like to know HOW LONG since the last dose of an injectable blood thinner can we obtain a fingerstick INR to ensure that the results are accurate? 5 hrs? 7hrs? 12hrs?24hrs? Or do we draw a serum level until when??

lovenox half like is 4.5 hrs

lovenox half life is 4.5 hrs

Given that INR is not affected by heparin, arixtra, or lovenox, I'd assume that it doesn't make any difference. Someone correct me if I'm wrong please.

Thank you all for your replies! That's what I have been instructing our home health nurses (but I wasn't quite sure) to wait at least 5-7hrs from last dose of lovenox/arixtra just to be sure that the results taken via portable INR machine is accurate.To mama_d... Heparin does not need monitoring but for the other injectables, PT/INR levels are still monitored(at least that's what the MDs we work with wants--they order PT/INR levels). It may not be the case for all patients on these meds.

I wonder what the rationale is, since they don't affect the INR. If you know, fill me in please!We do draw INRs on our pts who are on lovenox/heparin and Coumadin, since the goal is to get them onto Coumadin only as soon as we can. But we generally don't draw any levels to check the injectables since they've got such a short half-life. (Acute care setting, BTW.)