In this in vitro study, minimal changes in platelet function were noted after warming. (Image source: Thinkstock)
In this in vitro study, minimal changes in platelet function were noted after warming. (Image source: Thinkstock)

Do you warm platelets while they are being infused?  If so, you are violating guidelines published by the AABB, formerly known as the American Association of Blood Banks.  But does warming platelets affect platelet function?

In the study “Stored Platelet Functionality Is Not Decreased After Warming with a Fluid Warmer,” Dr. Gerhardt Konig, Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA and colleagues sought to determine whether warming platelets in a routine blood warmer had any effect on platelet function.

The authors obtained ten units of 3-day-old, platelet-rich plasma–derived whole blood platelets from their local blood bank.  They measured platelet aggregometry and maximum clot amplitude was determined using thromboelastography.  Platelet temperature was 22.4°C before warming, and after warming it was 37.8°C.  Both platelet aggregometry and measured maximum clot amplitude were no different before versus after warming, though with 5 μM adenosine diphosphate as agonist, platelet aggregometry decreased 5% after warming.

Patients can easily get cold.  The volume of 4-5 units of platelets is equivalent to a unit of blood, which we do warm.  As the authors note, however, their study sample was small, though a larger study would involve the diversion of more units of blood from the blood bank.  There may be changes in platelet function that were not measured by the authors.  In addition, this was an in vitro study: whether there would be different findings if in vivo clotting function was determined using actual patients, instead of measuring platelet function in the test tube is not clear.

Of course, platelets warm up to body temperature after they enter the blood stream, just like everything else we give intravenously. So whether or not warming affects in vitro measurements of function may matter little since it warming is inevitable in clinical use.