Several diagnostic criteria for serotonin syndrome have been proposed. The Hunter Serotonin Toxicity Criteria are the most accurate (sensitivity of 84%, specificity of 97%)
The diagnosis of serotonin syndrome is based on a history of taking a serotonergic agent and clinical findings. No labs are needed. To fulfill the Hunter Criteria, a patient must have taken a serotonergic agent and meet ONE of the following conditions:
- Spontaneous clonus
- Inducible clonus PLUS agitation or diaphoresis
- Ocular clonus PLUS agitation or diaphoresis
- Tremor PLUS hyperreflexia
- Hypertonia PLUS temperature above 38ºC PLUS ocular clonus or inducible clonus
Expressed differently,
To diagnose serotonin syndrome, the patient must have taken a serotonergic medication and also have one of the primary symptoms. Note that with the exception of spontaneous clonus, all primary symptoms will need an additional secondary symptom to confirm the diagnosis of serotonin syndrome.
Image from Am J Case Rep. 2016; 17: 347–351.
Reference / Further Study
Perioperative Diagnosis and Treatment of Serotonin Syndrome Following Administration of Methylene Blue. The American Journal of Case Reports. 2016;17:347-351. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4917068/