I was aked by my lab director if there is a valid reason for drawing a 3-5 mL discard tube before drawing a platelet function assay tube? After a limited search, I can find no information supporting the theory of drawing a discard tube before any coagulation test. What are your thoughts?
Hello, and thank you for your question. You are correct, there is no need to collect a discard tube before collecting a tube for any coagulation test, including platelet function testing. This is documented in the Clinical and Laboratory Standards Instituteguideline H21-A5, Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline – Fifth Edition. Order of draw is also addressed in guideline H18-A4, Procedures for the Handling and Processing of Blood Specimens for Common Laboratory Tests; Approved Guideline – Fourth Edition. The principle that a discard tube should be collected to eliminate “tissue fluid” from the assay specimen is “expert opinion” that has been discredited by results of several careful studies published in the 1990s and cited in the two guidelines. Geo.
George is correct that you do not need to draw a discard tub
George is correct that you do not need to draw a discard tube before any coagulation test UNLESS you happen to be using a butterfly or variable tubing blood collection system. In this case a discard tube is required since the air in the tubing will result in an underfilled first tube, which should not be used for any coagulation studies.
Thank you for this, Dr. F, very helpful. I’d like to direct everyone to my audio module on hemostasis specimens that is on this web site. It goes into detail on order of draw and collection with butterfly tubing. Geo.