Fever or hyperthermia: how to tell them apart and why it matters
Which statement about fever and hyperthermia is correct?
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A. In fever, pyrogens raise the hypothalamic set point; in hyperthermia the set point is normal and heat exceeds the capacity to dissipate it, so antipyretics only work in fever
Correct. Antipyretics block the prostaglandin synthesis that resets the thermostat; in hyperthermia (heat stroke, seizures, exercise, tremorgenic toxins) the thermostat is unchanged and treatment is cooling and addressing the cause.
B. A temperature above 41 °C almost always indicates fever of infectious origin
It is the other way round: fever rarely exceeds 41 °C because the body regulates it; extreme temperatures are more typical of hyperthermia (heat stroke, status epilepticus, intoxications).
C. Fever should be actively cooled with cold water and fans, just like heat stroke
The febrile animal defends its raised set point: it shivers and vasoconstricts, consuming more energy and oxygen. Active cooling is reserved for hyperthermia or extreme fever.
D. NSAIDs are the treatment of choice to lower temperature in heat stroke
They do not lower the temperature because the set point is normal, and they are dangerous: heat stroke involves hypovolaemia, kidney injury and a risk of DIC and gastrointestinal ulceration.
lightbulb Key takeaway
History (heat, exercise, seizures, toxins) and behaviour help: the febrile animal seeks warmth and may shiver; the hyperthermic animal pants and seeks the cold. With fever, find and treat the cause; with hyperthermia, cool to about 39.5 °C and stop to avoid hypothermia.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.