title: Plasma anti-FXa level as a surrogate marker of the adequacy of thromboprophylaxis in critically ill patients: A systematic review.
abstract: BACKGROUND
  Critical care patients are prone to venous thromboembolism (VTE) and, thus, pharmacological thromboprophylaxis is generally advised. Low-molecular weight heparins (LMWHs) have become the drug of choice in ICU patients, since their predictable and reproducible dose response. Monitoring their pharmacological effect is not usually necessary except in special occasions (i.e. with obese or renal failure patients), where anti-FXa level measuring is recommended. However, there is neither recommendation of adequate anti-FXa levels in critically ill patients nor is it known whether peak or trough level should be measured. The aim of this systematic review was to evaluate the recommended LMWH doses, and the reasons to monitor anti-FXa levels.
  
  
  METHODS
  We searched MEDLINE, Scopus, Cochrane Central Register of Controlled Trials and ClinicalTrials.com to identify all potentially relevant studies. Prospective studies done in critically ill patients were included if at least one anti-FXa level (i.e. peak or trough) after any specified LMWH thromboprophylaxis dose was measured.
  
  
  RESULTS
  Total 18 eligible studies including 1644 patients were included. There was a wide variation in the median peak anti-FXa levels (<0.1-0.35IU/ml). Trough levels were generally low. Of note, none of the studies detected any correlation with bleeding events and anti-FXa levels. Low trough level increased incidence of DVT in one study only.
  
  
  CONCLUSIONS
  Based on the current literature, no definite conclusions can be drawn on targeted anti-FXa level in critically ill patients when using LMWH thromboprophylaxis.
authors.affiliation: Tampere University Hospital, Critical Care Medicine Research Group, PO Box 2000, Tampere 33521, Finland. Electronic address: annukka.vahtera@pshp.fi.
authors.forename: Annukka
authors.initials: A
authors.lastname: Vahtera
authors.affiliation: Intensive Care Medicine, Department of Perioperative, Intensive Care and Pain Medicine, University of Helsinki, Helsinki University Hospital, PO Box 340, Helsinki 00029, Finland.
authors.forename: Suvi
authors.initials: S
authors.lastname: Vaara
authors.affiliation: Intensive Care Medicine, Department of Perioperative, Intensive Care and Pain Medicine, University of Helsinki, Helsinki University Hospital, PO Box 340, Helsinki 00029, Finland.
authors.forename: Ville
authors.initials: V
authors.lastname: Pettilä
authors.affiliation: Tampere University Hospital, Critical Care Medicine Research Group, PO Box 2000, Tampere 33521, Finland.
authors.forename: Anne
authors.initials: A
authors.lastname: Kuitunen
mesh_terms: D000925:Anticoagulants / Q000097:blood / Q000627:therapeutic use*; D016638:Critical Illness / Q000628:therapy; D016903:Drug Monitoring; D065427:Factor Xa Inhibitors / Q000097:blood / Q000627:therapeutic use*; D006470:Hemorrhage / Q000139:chemically induced; D006495:Heparin, Low-Molecular-Weight / Q000097:blood / Q000627:therapeutic use*; D006801:Humans; D054556:Venous Thromboembolism / Q000097:blood / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight
keywords: Anti-FXa; Critical care; LMWH; Monitoring; Thromboprophylaxis