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Diagnosis of venomous snake bites
Last reviewed: 03.07.2025
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Along with the clinical manifestations of snakebite poisoning, a definitive diagnosis requires identification of the snake species. The history should include the following:
- bite time;
- description of the snake;
- assistance provided on site;
- patient's condition;
- presence of allergy to horse and sheep antidotes;
- history of snake bites and treatment.
A complete clinical examination is necessary, including measurement of limb circumference proximal and distal to the bite site.
Patients often cannot recall details of the snake's appearance. Rattlesnakes differ from nonvenomous snakes in their head shape, elliptical pupils, heat-sensing pits between the eyes and nose, retractable fangs, and a series of subcaudal plates beginning at the anal plate on the underside of the tail.
Coral snakes in the United States have round pupils and a black snout, but no facial pits. Their heads are blunt or cigar-shaped and have alternating red, yellow (cream), and black bands. Because of this, they are often mistaken for the common nonvenomous scarlet kingsnake, which has red, black, and yellow bands ("red on yellow kills," "red on black is not very venomous"). Coral snakes have short, fixed fangs and inject venom with a series of chewing motions. Fang marks are suggestive but not diagnostic; rattlesnakes may leave single or double fang marks or other marks, while bites by nonvenomous snakes usually leave multiple superficial marks. However, the number of fang marks and the location of the bite may not be normal because snakes may bite multiple times.
A dry rattlesnake bite can be diagnosed if signs of poisoning do not appear for more than 8 hours.
The severity of poisoning depends on the size and species of snake (rattlesnakes, copperheads, copperheads), the amount of venom injected, the number of bites, the location and depth of the bite (for example, bites to the head and torso are more dangerous than bites to the extremities), age, height-to-weight ratio, the health of the victim, the time until first aid is provided, and the victim's susceptibility to the venom.
Poisoning is classified as mild, moderate, or severe. Classification is based on the severity of local manifestations, systemic symptoms, coagulation parameters, and laboratory data. Severity is determined by the worst symptoms and laboratory data. Poisoning can progress rapidly from mild to severe, which requires constant monitoring.
[ Severity of poisoning after pit viper bites
Degree |
Description |
Easy |
Changes only at the bite site, no systemic manifestations, negative laboratory test results |
Moderate |
Changes extend to areas outside the bite; non-life-threatening systemic manifestations (eg, nausea, vomiting, paresthesia); minor coagulation or laboratory changes without clinically significant bleeding |
Heavy |
Pathological changes affecting the entire limb; severe systemic manifestations (eg, hypotension, dyspnea, shock); changes in coagulation and laboratory data with clinically significant bleeding |