July 2024 Quick Question: Specimen Storage

Our July 2024 Quick Question, which drew 58 responses, asked, “How long may you store a specimen after collection for a PT test?” Our answers were:

1. 1 hr: 2 (3%)
2. 4 hrs: 19 (33%)
3. 8 hrs: 7 (12%)
4. 24 hrs: 30 (52%, the correct answer)

This question draws attention to the March 2024 publication of the latest edition of CLSI H21; here’s the reference: Clinical and Laboratory Standards Institute (CLSI). Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays. 6th ed. CLSI guideline H21 (ISBN 978-1-68440-228-1 [Print]; ISBN 978-1-68440-229-8 [Electronic]). Clinical and Laboratory Standards Institute, USA, 2024.

From CLSI H21:

1. Whole blood specimens for PTT or anti-Xa assays for UFH are stable at ambient temperature for 1 hour.
2. Whole blood specimens for FVIII, FXII, antiplasmin, plasminogen, or protein S activity assays are stable at ambient temperature for 4 hours.
3. Whole blood specimens for PTT when no UFH is present are stable at ambient temperatures for 6–8 hours.
4. Whole blood specimens for PT/INR are stable at ambient temperatures for 24 hours.

Further specimen management information is available in the document. Dr. Emmanuel Favaloro offered this comment on July 2, 2024: “The Quick Question could raise a separate intention: how long do labs store samples once PTs (or normal coag tests) are performed? In Australia, we follow NPAAC guidelines which mandate these be stored a minimum of 1 week before discarding–this is mostly to ensure the ability to check sample identity should there be any question about the results, with add-on testing being limited to just 24 hours in most cases.”