From Carla Purvis, MT (ASCP) SH, Parkview Regional Medical Center in Fort Wayne: Hi, George. We have acute care clinicians requesting temperature correction for prothrombin time results for patients who have clinically induced
hypothermia. CAP standards state prothrombin times must be performed at 37C. Do you have any references for performing temperature corrections? Thanks.
Hi, Carla. Just when I thought we’d discussed everything about hemostasis, a new idea comes along. Hypothermia is defined as a a body core temperature of 35C or lower. Therapeutic hypothermia, targeting 32 or 33C, has become an effective management strategy to prevent brain injury subsequent to cardiac arrest and during extracorporeal circulation. Hypothermia seems to suppress surgery-induced inflammation at least during the procedure, and appears to help restore cognitive function even in people whose circulation is compromised for several minutes. Conversely, emergency technicians and emergency department staff work to reverse acute shock-related hypothermia in trauma victims.
Given that enzyme function slows as temperatures drop, it stands to reason that cold could induce coagulopathy with the risk of bleeding. It would make sense to perform coagulation assays at in vitro temperatures matching the patient’s temperature and to have reference intervals for comparison, both in therapeutic and shock-related hypothermia. This assumes we have instruments whose incubation and assay temperatures can be adjusted to operate at 32 or 33C and we have a way to validate the modification and to establish reference intervals so that we can make valid clinical judgments from our results. It may be that this is best accomplished using near-patient testing of freshly collected blood specimens, given that we would be compelled to manage specimens at matching temperatures if we are to transport or store them for any time period.
A simpler alternative may be to simply apply existing technology to establish reference parameters for controlled hypothermic periods, provided we can demonstrate differences using standard approaches.
I found one fairly well-powered study, attached here, conducted in Denmark using the ROTEM and Multiplate at 33 and 37C to test patients at 37C, then chilled to 33C during a procedure, and then rewarmed to 37C. This group found little difference among ROTEM assays and Multiplate agonists and concluded there was nothing to be gained by running assays at 33C. I suspect this topic may attract additional comments from clotters around the world who have developed data on hypothermia-related hemostasis parameters.
Here’s the article from Denmark: /sites/default/files/hypothermia_jeppeson_crit_care_2016.pdf
In 2006 at the ASH meeting in
In 2006 at the ASH meeting in San Diego this topic was brought up in an open session on hypothermia. The military had an interest in this issue due to the transport of troops in military aircraft and the cold temperatures encountered. Hypothermia can affect the lab results but trying to correlate these findings with actual clinical data on the multitude of photo-optic and mechanical reagent/instrument combinations is almost impossible. Mainly because all of the coagulation reagents are designed to operate at 37 degree C. I stood up and asked the question, “Should we modify our instruments and reagents to match the temperature of the patient experiencing hypothermia?” The panel were all in agreement that this emphatically should not be accomplished. I worked on several studies when I was employed for the military on this issue on animal subjects and found little correlation that yielded little clinical relevance.
David L. McGlasson, MS, MLS(ASCP)cm San Antonio, TX.
Temperature adjustment for
Temperature adjustment for TEG: Do not recommend temperature adjustment. You can adjust the temperature with TEG but all other coag tests are done at 37 degrees. If the core temp is below 35 degrees, the thrombin generation will be substantially reduced. Oksana Volod, MD
Two more references how
Two more references about how hypothermia affects PT and PTT values in pooled/reference plasma are below: Effect of hypothermia on the coagulation cascade http://www.ncbi.nlm.nih.gov/pubmed/1395660, and Hypothermia and blood coagulation: dissociation between enzyme activity and clotting factor levels http://www.ncbi.nlm.nih.gov/pubmed/2253317.
I think, the knowledge of PT/PTT values in hypothermic conditions is not clinically helpful without appropriate reference values, established for each test in particular temperature.