A new specimen question from Pam Owens, TriCore Laboratories:
Hi George, this is a question with two parts. Given that a PT is stable for 24 hrs in the original tube with the top on (never removed)…
1. How long is the sample good once the top has come off?
2. If the plasma has been removed, frozen and thawed, what is the PT stability then?
We sometimes get requests for a PT to be added to a specimen and when one of these things has occurred we are never quite sure at what point to say no. Thanks, Pam.
Hi, Pam. I’ve not found any stability data for fresh, opened specimens, but CLSI H21-A5requires thawed specimens to be “tested immediately.” The CLSI requirement is unreferenced, but we do know that the pH of opened specimens rises rapidly, and pH profoundly affects enzyme reaction rates, so it is probably appropriate to require that fresh or thawed open specimens to be tested immediately. There may be some value in experimentally confirming this conclusion. For more on plasma stability, see also Normal Plasma Storage.
Reference: Clinical and Laboratory Standards Institute (CLSI). Collection, transport, and processing of blood specimens for testing plasma-based coagulation assays and molecular hemostasis assays, approved guideline–Fifth Edition, CLS document H21-A5. CLSI, 940 West Valley Road, Suite 1400, Wayne, PA 19087-1898, USA, 2008.