Ann Marie Frey, an infusion nurse specialist from Childrens Hospital in Philadelphia, would be the best person to reply. She is the author of a review article on drawing blood samples. I am most familiar with nurses adding the heparin to the syringe rather than a syringe purchased with the heparin already in it. Also, I am not sure what you mean by micro-containers. Lynn

Returning the "waste" blood is never a good idea. The only acceptable method would be to hold that "waste" blood in a heparinzed syringe attached to a stopcock. I would never, under any circumstances, detach this syringe and set it aside while I drew the actual blood sample and then  return it to the patient, at any age. This has been studied and found to return clots and possible organisms. Lynn