The single preferred test for monitoring systemic anticoagulation during veno-venous extracorporeal membrane oxygenation. Herein we compare the frequency of monitoring anticoagulation with the activated partial thromboplastin time (aPTT), the activated clotting time (ACT), or the anti-Xa between centers, classified according to the following criteria: (1) university hospital or not; (2) registered with the Extracorporeal Life Support Organization (ELSO) or not; (3) 2017 gross national income per capita, categorized as high (at least $12,056 USD) or non-high (less than $12,056 USD); (4) primary patient population, categorized as adult-only, pediatric-only, or mixed; (5) annual extracorporeal membrane oxygenation patient volume, categorized as high (more than 20 cases per year), intermediate (10 to 20 cases per year), or low (less than 10 cases per year). Bars and labels are percentages of respondents. P values refer to chi-squared test.