To balance the risk of bleeding versus circuit thrombosis during extracorporeal life support (ECLS), it is important to monitor anticoagulants and hemostasis. We evaluated the prothrombin time (PT), partial thromboplastin time (PTT), activated clotting time (ACT), and antifactor Xa heparin activity (aXa) correlation with changes in coagulation factor and heparin levels using in vitro and in vivo samples. aXa correlated with heparin (r2 = 0.97) and antithrombin (r2 = 0.98) but was unaffected by other parameters. PT correlated with coagulation factors (r2 = 0.88) but was minimally affected by heparin or other parameters. When single parameters were changed, ACT was insensitive to <0.5 U/ml heparin, correlated with coagulation factors (r2 = 0.93), and was affected by factor XII and platelets. When multiple parameters changed in vitro and in vivo, ACT was not correlated with heparin or coagulation factors. PTT correlated with heparin and coagulation factors individually but had low correlation when multiple parameters changed in vitro and in vivo. In conclusion, aXa is the most specific for heparin levels, and PT is most specific for coagulation factor levels making these assays well suited to monitor anticoagulation and hemostasis for patients on ECLS. PTT is highly variable when multiple parameters are changing in vitro and in vivo, but may be useful when aXa cannot be used because of interference. ACT is too insensitive to heparin, sensitive to too many other factors, and too imprecise to be useful for monitoring hemostasis during ECLS.
From the *Department of Laboratory Medicine, BloodWorks Northwest, Seattle, Washington
†Department of Laboratory Medicine, University of Washington, Seattle, Washington
‡Seattle Children’s Hospital, Seattle, Washington
§Department of Pediatrics, University of Washington, Seattle, Washington
¶Division of Cardiothoracic Surgery, Department of Surgery, University of Washington, Seattle, Washington
‖Division of Hematology and Oncology, Department of Pediatrics, University of Washington, Seattle, Washington.
Submitted for consideration October 2018; accepted for publication in revised form February 2019.
Disclosure: The authors have no conflicts of interest to report.
Correspondence: Wayne L. Chandler, Department of Laboratories, OC.8.720, Seattle Children’s Hospital, 4800 Sandpoint Way NE, Seattle, WA 98105. Email: firstname.lastname@example.org.