Changes in serial laboratory test results in snakebite patients: when can we safely exclude envenoming?
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.
Ireland
Graham
G
Emergency Department, Gold Coast Hospital, Gold Coast, QLD, Australia.
Brown
Simon G A
SG
Buckley
Nicholas A
NA
Stormer
Jeff
J
Currie
Bart J
BJ
White
Julian
J
Spain
David
D
Isbister
Geoffrey K
GK
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
D003402:Creatine Kinase