Rattlesnake Envenomation Workup

Updated: Mar 14, 2023
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Laboratory Studies

Coagulopathy commonly occurs with rattlesnake envenomation, although clinical bleeding is uncommon. [15, 16, 17, 18, 19] Defibrination and/or thrombocytopenia most often characterize snakebite coagulopathy. Defibrination is manifested by low serum fibrinogen, elevated prothrombin time, and elevated fibrin split products (FSP). Venom-induced thrombocytopenia may exist in association with or independently of defibrination. Abnormal coagulation parameters may last for a week or more. Recurrence of coagulopathy after resolution with antivenom has been reported.

  • Complete blood cell (CBC) count with differential

  • Platelets

  • Prothrombin time

  • Activated partial thromboplastin time

  • Fibrinogen

  • Type and screen

  • Urinalysis

  • Thromboelastography

Rhabdomyolysis may occur from severe envenomation but is best described after canebrake (Crotalus horridus atricaudatus) [20] and Mojave (Crotalus scutulatus) [21] rattlesnake envenomations. Rhabdomyolysis may lead to myoglobinuric renal failure and subsequent electrolyte abnormalities, such as hyperkalemia, hypokalemia, or hypocalcemia.

  • Creatine kinase (CK)

  • Electrolytes

  • Blood urea nitrogen (BUN), creatinine

  • Calcium

  • Phosphorus

  • Urinalysis

For respiratory difficulty, consider arterial blood gases (ABGs), although arterial puncture should be avoided if a severe venom-induced coagulopathy develops.

Obtain laboratory and other diagnostic data on a case-by-case basis. Factors to consider may include severity of envenomation, physician preference, and cost.


Imaging Studies

Plain radiographs may depict teeth or fangs retained in the wound.

Consider a head CT scan if the patient has a headache or altered level of consciousness (ALOC) with a severe coagulopathy.


Other Tests

Obtain an electrocardiogram (ECG), if indicated.

Skin testing is not necessary before administering either Crotalidae polyvalent immune Fab, ovine (CroFab) or Crotalidae immune Fab, equine (Anavip) antivenins.



Central venous or interosseous access may need to be obtained. However, avoid placing a central line in a noncompressible site (eg, internal jugular) because of the risk of bleeding from venom-induced coagulopathy.

Fasciotomy may be indicated if measured compartment pressures remain persistently and severely elevated despite adequate antivenom. CroFab has been shown to limit the decrease in perfusion pressure associated with compartment syndrome. Compartment syndrome may manifest subjectively, with complaints of increasing pain, and objectively, with tenderness on passive muscle stretch, a rock hard feel to the compartment or a diminished capillary refill. True compartment syndrome is rare following snakebite, even in patients with severe edema, because most envenomations are believed to be subcutaneous. Myonecrosis has been shown to occur from direct myotoxicity, even after fasciotomy of the affected compartment.

Distinguishing compartment syndrome from the effects of envenomation may be difficult. Similar to compartment syndrome, rattlesnake envenomation may cause a bluish discoloration of the skin or pallor (because of subcutaneous bruising), severe swelling, paresthesias, and pain. If effects are only caused by envenomation and the patient does not have compartment syndrome, capillary refill is normal and compartmental pressure is not elevated.