Snakebite Workup

Updated: Apr 09, 2021
  • Author: Spencer Greene, MD, MS, FACEP, FACMT, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Laboratory Studies

Patients with possible snakebite envenomation should have the following laboratory tests performed:

  • Complete blood cell count
  • Basic metabolic profile
  • Prothrombin time
  • Fibrinogen value
  • Creatine kinase value

Patients with systemic toxicity may warrant additional testing, including liver function tests, urinalysis, blood type and crossmatch, and venous blood gas analysis. Rotational thromboelastometry and thromboelastography are not readily available in many healthcare settings but may have a greater role in evaluating patients for hematotoxicity in the future.

Routine measurement of D-dimer and fibrin split products is not necessary because the results do not change management.

Hematologic toxicity is frequently observed following crotalid envenomation. It may be present on arrival or it may develop after several days. Specific laboratory abnormalities may include the following:

  • Coagulopathy (prothrombin time >15 seconds)
  • Hypofibrinogenemia (fibrinogen < 150 mg/dL)
  • Thrombocytopenia (platelet count < 150 x 10 3/µL)

In general, copperhead envenomations are associated with the least hematotoxicity. In a study of copperhead envenomations in Virginia, only 14% of copperhead envenomations had any type of hematologic toxicity. [39] A similar percentage of patients developed thrombocytopenia in a study conducted in the Carolinas, although coagulopathy and hypofibrinogenemia were observed in 24% and 63% of patients, respectively. [38]

Coagulopathy was observed in 19% of patients in a multicenter study of cottonmouth envenomations. [40]

Hematologic toxicity was seen in 76% of patients with rattlesnake envenomations. In the same population, 24% of patients had late hematotoxicity. In a study of high-risk snakebite victims, late coagulopathy was present in 32% of subjects. [25, 41]


Imaging Studies

Routine imaging is not required following snake envenomation. Conventional radiographs of the affected extremity should be considered if there is suspicion for a retained fang or if the diagnosis is uncertain. Chest radiography should be performed in patients with systemic toxicity experiencing dyspnea. Rarely, neuroimaging may be necessary to look for intracranial bleeding in patients with altered mental status.

Ultrasonography of the affected extremity should be obtained in patients when the diagnosis is uncertain and there is clinical concern for a deep venous thromboembolism.


Other Tests

Clinicians should examine the affected extremity for swelling, tenderness, hemorrhagic blebs, and the presence of strong distal pulses. The proximal spread of tenderness and swelling should be recorded every 15-30 minutes to document the progression of the local venom effects. This can be accomplished by palpating the proximal part of the affected extremity and moving distally until tenderness is elicited.

Serial dynamometry and negative inspiratory force assessments should be measured on patients at risk for respiratory and/or skeletal weakness/paralysis (eg, coral snake envenomations, bites from neurotoxic rattlesnakes). Capnography may also be used to identify patients with mild respiratory insufficiency.

True compartment syndrome is exceptionally uncommon following snake envenomation. However, compartmental pressures should be measured in patients with disproportionate pain and significant tissue swelling. Commercially available devices exist that are sterile, simple to assemble and read, and reliable (eg, Stryker pressure monitor).