Our April, 2010 Quick Question was “Do you collect a discard tube prior to collecting a tube for coagulation testing?”
a. Never: 14 (34%)
b. Always: 14 (34%)
c. Only for special coagulation testing: 13 (32%)
For those who are collecting a discard tube in all cases, I have good new for you, you can stop. Studies by Adcock, Kressin and Marlar, and others by McGlasson and byBamberg are cited in Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays; Approved Guideline—Fifth Edition. CLSI document H21-A5 Clinical and Laboratory Standards Institute, 2008. All the studies conclude that the discard tube makes no difference, and that the coagulation tube should be collected first in a series of tubes.
For those who use a discard tube for special coagulation testing, you also can stop.Raijmakers MTM, Menting CHF, Vader HL, van der Graff F. Collection of blood specimens by venipuncture for plasma-based coagulation assays: necessity of a discard tube. Am J Clin Pathol 2010; 133: 331-5 found no clinical necessity for a discard tube when testing for partial thromboplastin time (PTT), antithrombin (AT), protein C, and factors II, V, VIII, IX, and X.
We can save resources, time, and reduce complexity by eliminating the discard tube. Of course, it is still necessary to collect a discard tube to compensate for the air space in a needle set, however, as the tubing contains approximately 0.5 mL of air.