title: Discordant aPTT and anti-Xa values and outcomes in hospitalized patients treated with intravenous unfractionated heparin.
abstract: BACKGROUND
  Both the activated partial thromboplastin time (aPTT) and anti-Xa assay can be used to monitor unfractionated heparin (UFH). Following implementation of an anti-Xa method for heparin dosing protocols in our hospital, we became aware of many patients with discordant aPTT and anti-Xa values.
  
  
  OBJECTIVE
  To determine the frequency of discordant aPTT and anti-Xa values in a large cohort of hospitalized patients treated with UFH, as well as the demographics, coagulation status, indication for UFH, and clinical outcomes in this population.
  
  
  METHODS
  All aPTT and anti-Xa values from adults hospitalized between February and August 2009 at Stanford Hospital who were treated with UFH were analyzed. All samples were drawn simultaneously. A polynomial fit correlating aPTT and anti-Xa with a 99% confidence limit was designed. Paired aPTT/anti-Xa values were grouped according to whether the paired values fell within or outside of the concordant area. Patients were placed into groups based on concordance status, and clinical outcomes were assessed.
  
  
  RESULTS
  A total of 2321 paired values from 539 patients were studied; 42% of data pairs had a high aPTT value relative to the anti-Xa value. Patients with elevated baseline prothrombin time/international normalized ratio or aPTT frequently demonstrated disproportionate relative prolongation of the aPTT. Patients with at least 2 consecutive high aPTT to anti-Xa values had increased 21-day major bleeding (9% vs 3%; p = 0.0316) and 30-day mortality (14% dead vs 5% dead at 30 days; p = 0.0202) compared with patients with consistently concordant values.
  
  
  CONCLUSIONS
  aPTT and anti-Xa values are frequently discordant when used to measure UFH in hospitalized patients. A disproportionate prolongation of the aPTT relative to the anti-Xa was the most common discordant pattern in our study. Patients with relatively high aPTT to anti-Xa values appear to be at increased risk of adverse outcomes. Monitoring both aPTT and Xa values may have utility in managing such patients.
authors: Department of Medicine (Hematology), School of Medicine, Stanford University, Stanford, CA, USA.
authors: Elizabeth A
authors: EA
authors: Price
authors: Jing
authors: J
authors: Jin
authors: Huong Marie
authors: HM
authors: Nguyen
authors: Gomathi
authors: G
authors: Krishnan
authors: Raffick
authors: R
authors: Bowen
authors: James L
authors: JL
authors: Zehnder
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D000991:Antithrombins / Q000097:blood*; D001777:Blood Coagulation / Q000187:drug effects*; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006470:Hemorrhage / Q000139:chemically induced* / Q000453:epidemiology / Q000401:mortality / Q000517:prevention & control; D006493:Heparin / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D006785:Hospitals, University; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D009026:Mortality; D010314:Partial Thromboplastin Time; D012189:Retrospective Studies; D012306:Risk; D055502:Secondary Prevention; D013927:Thrombosis / Q000097:blood / Q000453:epidemiology / Q000401:mortality / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants; D000991:Antithrombins; D006493:Heparin