title: Changes in serial laboratory test results in snakebite patients: when can we safely exclude envenoming?
abstract: OBJECTIVE
  To determine which laboratory tests are first associated with severe envenoming after a snakebite, when (ie, how long after the bite) the test results become abnormal, and whether this can determine a safe observation period after suspected snakebite.
  
  
  METHODS
  Prospective cohort study of 478 patients with suspected or confirmed snakebite recruited to the Australian Snakebite Project from January 2002 to April 2009, who had at least three sets of laboratory test results and at least 12 hours of observation in hospital after the bite. Severe envenoming was defined as venom-induced consumption coagulopathy (VICC), myotoxicity, neurotoxicity or thrombotic microangiopathy.
  
  
  METHODS
  International normalised ratio (INR), activated partial thromboplastin time (aPTT), creatine kinase (CK) level, and neurological examination.
  
  
  RESULTS
  There were 240 patients with severe envenoming, 75 with minor envenoming and 163 non-envenomed patients. Of 206 patients with VICC, 178 had an INR > 1.2 (abnormal) on admission, and the remaining 28 had an INR > 1.2 within 12 hours of the bite. Of 33 patients with myotoxicity, a combination of CK > 250 U/L and an abnormal aPTT identified all but two cases by 12 hours; one of these two was identified within 12 hours by leukocytosis. Nine cases of isolated neurotoxicity had a median time of onset after the bite of 4 hours (range, 35 min - 12 h). The combination of serial INR, aPTT and CK tests and repeated neurological examination identified 213 of 222 severe envenoming cases (96%) by 6 hours and 238 of 240 (99%) by 12 hours.
  
  
  CONCLUSIONS
  Laboratory parameters (INR, aPTT and CK) and neurological reassessments identified nearly all severe envenoming cases within 12 hours of the bite, even in this conservative analysis that assumed normal test results if the test was not done.
authors.affiliation: Emergency Department, Gold Coast Hospital, Gold Coast, QLD, Australia.
authors.forename: Graham
authors.initials: G
authors.lastname: Ireland
authors.forename: Simon G A
authors.initials: SG
authors.lastname: Brown
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Buckley
authors.forename: Jeff
authors.initials: J
authors.lastname: Stormer
authors.forename: Bart J
authors.initials: BJ
authors.lastname: Currie
authors.forename: Julian
authors.initials: J
authors.lastname: White
authors.forename: David
authors.initials: D
authors.lastname: Spain
authors.forename: Geoffrey K
authors.initials: GK
authors.lastname: Isbister
mesh_terms: D000328:Adult; D000465:Algorithms; D003402:Creatine Kinase / Q000097:blood; D019091:Critical Pathways; D004211:Disseminated Intravascular Coagulation / Q000175:diagnosis* / Q000209:etiology*; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D009460:Neurologic Examination; D010314:Partial Thromboplastin Time; D011446:Prospective Studies; D012909:Snake Bites / Q000097:blood / Q000150:complications*; D055815:Young Adult
chemical_list: D003402:Creatine Kinase