A contributor asks, “has sb reported shorter clotting times when using 3.8% (0.129M) sodium citrate tubes than 3.2% (0.109M) tubes? literature and the logic says the opposite.”
Hello, and thank you for your question. I’m unsure of your reference to “sb,” however I agree that it is logical to presume that the 3.8% sodium citrate concentrations used in blue-closure coagulation tubes before 2000 could factitiously prolong prothrombin times and partial thromboplastin times, especially if the tubes were underfilled to 90% or less. Several publications in the late 1990s confirmed this, perhaps the most definitive wereAdcock DM, Kressin DC, Marlar RA, Minimum specimen volume requirements for routine coagulation testing: dependence on citrate concentration. Am J Clin Pathol 1998;109:595–9, and McGlasson DL, A review of variables affecting PTs/INRs. Clin Lab Sci 1999;12):353–8, upon which the recommendations in CLSI H21-A5 are based. Indeed, 3.8% tubes are no longer readily available.
One caveat, the switch from 3.8% to 3.2% sodium citrate was never validated for platelet aggregometry, and there may be instances in which 3.8% citrate provides better clinical efficacy, as documented in McGlasson DL, Shah AD, Fritsma GA. Ability of the INNOVANCE PFA P2Y system to detect clopidogrel-induced ADP receptor blockade in preangiocath individuals. Blood Coagul Fibrinolysis. 2011;22 :583–7. If you choose to act on this concern, you may have to prepare your own tubes. Geo.