From George: Long ago at a Temple University-sponsored meeting in Philadelphia, Dr. Dorothy Adcock provided data showing it was unnecessary to collect a “discard” tube ahead of a blue-closure hemostasis specimen.
Conventional wisdom prior to hers and the work of others was that a discard tube was necessary to avoid contamination with “tissue thromboplastin,” which could interfere. I naively asked Dr. Adcock, “What about traumatic venipunctures?” to which she responded she’d not been able to consent subjects to agree to a traumatic venipuncture!”
Now we no longer require a discard tube unless collecing through an infusion set (just to offset the volume of air in the set), but we still state that it is necessary to avoid traumatic venipunctures when collecting hemostasis specimens. Yesterday Dave McGlasson asked if I knew of any data that proves a traumatic venipuncture affects coagulation laboratory results, so I told him the story of Dr. Adcock and my question. I’ve never seen data on this, and presume the requirement is based on pure logic and expert opinion. Does any of our participants have something to add? A reference or data, perhaps? Please comment below.
Reference: McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: is a second tube necessary? Clin Lab Sci.1999;12:137–9.
With the above comments
With the above comments being put forward I would like to plead to educators in Medical Laboratory Science to please stop teaching the tissue thromboplastin contamination by a traumatic puncture issue. It is a myth that we have researched as far back as 1948 without any data being discovered. The discard tube has been discredited except for drawing out of IV lines or infusion collection devices. Lets put this one in the graveyard of lab myths.
From George, I challenge Dr.
From George, I challenge Dr. Favaloro’s assertion that traumatic venipuncture is a cause for hemolysis. First, there is no particular reason to contend that ICU or emergency room blood collectors are somehow more prone to traumatic venipuncture than others. Second, why should traumatic venipuncture cause hemolysis, presuming the blood flows freely subsequent to the start? I contend that hemolysis results from collecting blood while starting an IV. The IV equipment is, regrettably, not designed for blood collection, only for infusion, so withdrawing blood through the canula, especially with force, is the apparent mechanism.
And a contrasting quote from
And a contrasting quote from Dr. Emmanuel Favaloro, also responding to Dave:
“Tissue thromboplastin release from ‘traumatic venipuncture’ is one of those things that we accept as it makes sense; not sure anyone ever proved it–old literature would not have the methods available to test for ’tissue thromboplastin’ other than shortening of clotting times, and you wouldn’t be ethically permitted to cause ‘traumatic venipuncture’ to prove it’s release.
Not sure we always need evidence. We may have enough evidence to suggest that ‘traumatic venipuncture’ occurs and causes haemolysis–certainly a problem with our ICU dept, and I know that there is some literature out there about high levels of haemolyisis in ICU departments. Does that help?
From George: I’m posting a
From George: I’m posting a response from Dennis Ernst, Center for Phlebotomy Education, to Dave McGlasson, the inspiration for this post.
“Evidence does not exist that tissue thromboplastin ever gets into samples from a venipuncture (or skin puncture), much less affects coag results, even factor assays. Plenty of evidence exists that it does not.”