142: impact of c-reactive protein on anticoagulation monitoring in extracorporeal membrane oxygenation

Introduction: Thrombotic and hemorrhagic complications are a significant contributor to morbidity and mortality in patients supported with extracorporeal membrane oxygenation (ECMO). The impact of inflammation on anticoagulation monitoring in ECMO is unknown. Methods: We conducted a prospective, single-center, observational cohort study of patients supported on ECMO treated with heparin for systemic anticoagulation. C-Reactive protein (CRP) levels were measured as a surrogate for overall inflammation. The relationship between CRP and the partial thromboplastin time (PTT) was evaluated using a CRP-insensitive PTT assay (PTT-CRP) alongside standard PTT measurements. Results: We analyzed data from 30 patients anticoagulated with heparin over 371 ECMO days. CRP levels were significantly elevated (median 17.2 mg/dL, interquartile range, 9.2 – 26.1) and 93% of patients had a CRP > 5mg/dL (10-fold upper limit of normal) during their ECMO course. The median PTT (58.9 seconds (46.9 – 73.3)) was prolonged by 11.3 seconds compared to the simultaneously measured PTT-CRP (47.6 seconds (40.1 – 55.5), p< 0.001). The median difference between PTT and PTT-CRP generally increased with CRP elevation from 2.7 seconds for CRP < 5.0 mg/dL to 13.0 seconds for CRP between 5 to 10 mg/dL, 17.7 seconds for CRP between 10 to 15 mg/dL, and 15.1 seconds for CRP > 15 mg/dL (p < 0.001). A subgroup of patients was transitioned from heparin to argatroban; in these patients a similar difference was observed (PTT: 62.1 (53.0 – 78.5) vs. PTT-CRP: 47.6 (41.3 – 57.7), p< 0.001). Conclusions: Elevation in CRP is common in patients on ECMO and can falsely prolong PTT as measured by commonly used assays. The degree of discrepancy introduced due to CRP-interference is clinically important given narrow therapeutic PTT targets in this high-risk patient population and may contribute to the development of hematologic complications.