From Kim Kinney at Indiana University Health:
Hi George. We frequently get asked how long to stop an unfractionated heparin infusion before drawing for a partial thromboplastin time (PTT) from a central line or peripheral stick above the infusion site. We have always referred them to pharmacy. is there a standard practice used by nursing at other institutions that someone would share?
Hi, Kim, there is no waiting period established in CLSI Guidelines H3 and H21, nor in any of their references. I suspect that no one has made the effort to establish a time frame, as normal blood circulation would cause the circulating heparin level to rapidly stabilize. The key instructions for vascular access device (VAD) collection is given in Ernst DJ. Blood Specimen Collection FAQs, Center for Phlebotomy Education, 2008, which states, “If not possible to avoid, the line should be flushed with 5 mL of saline and the first 5 mL of blood, or six dead-space volumes of the VAD discarded if you are drawing coagulation tests.”
I hope this helps, and am eager to see if our contributors can add any additional information.