Here is a question forwarded by friend and colleague Dennis Ernst, Center for Phlebotomy Education. When we must draw from the arm with fluids infusing, our policy has always been that the RN must pause the IV. If the IV is in the other arm, we do not ask the nurses to pause the infusion no matter what is being infused or what is being drawn. This past week, we had a nurse get upset with us because the phlebotomist did not ask her to stop the heparin infusing so an anti-factor Xa could be drawn from the opposite arm. Should our policy be changed?
George responds, In this instance the nurse is wrong. We avoid collecting specimens from above or even below a flowing infusion site for the obvious reason that the venous blood is locally diluted by the IV fluid, but for most infusions, collecting from the opposite arm will provide a reliable result. There are a few instances where it is best to wait until the infusion is complete, such as red cell transfusions, but for most fluids, collecting from the opposite arm is good policy. In the case of unfractionated heparin I suggest that temporarily stopping the drip could even introduce an error, since UFH clears rapidly. For accuracy, you'd want the plasma level that reflects the current dosage.
I've sent this question along to an ICU RN who is our friend and colleague, as it would be valuable to have a nurse's perspective.