San Francisco Syncope Rule
Screen a patient who has fainted for short-term risk of a serious outcome with the San Francisco Syncope Rule. The five predictors spell CHESS — Congestive heart failure, Haematocrit below 30%, an abnormal ECG, Shortness of breath, and a Systolic blood pressure below 90 mmHg. If none is present the patient is low risk; any one present flags higher risk. Tick the features present to see the result.
About the San Francisco Syncope Rule
The rule flags patients after syncope who are at higher risk of a serious short-term outcome, to help decide who needs admission and monitoring. Source: Quinn J et al., “Derivation of the San Francisco Syncope Rule,” Annals of Emergency Medicine 2004; validation studies 2006–2008.
Frequently asked questions
What is the San Francisco Syncope Rule?
It is a five-item screen that identifies patients who have fainted (syncope) and are at higher short-term risk of a serious outcome such as a significant arrhythmia, myocardial infarction, major bleed or death within about 7–30 days. The five predictors are remembered by the mnemonic CHESS.
What does CHESS stand for?
C — a history of Congestive heart failure. H — Haematocrit below 30%. E — an abnormal ECG (a non-sinus rhythm, or new changes compared with a prior ECG). S — a symptom of Shortness of breath. S — a Systolic blood pressure below 90 mmHg at triage. Each is a yes/no item.
How is the result interpreted?
If none of the five is present, the patient is classified as low risk for a serious short-term outcome. If any one or more is present, the patient is not low risk and admission, monitoring and further investigation are generally advised. The rule is a screen, not a diagnosis, and identifies who needs more attention rather than what is wrong.
How reliable is the rule?
The original derivation reported around 96–98% sensitivity for serious outcomes, but later external validation studies found lower sensitivity (around 74% in some), meaning it can miss cases. Because of this, it should support rather than replace clinical judgement, and a low-risk result does not on its own guarantee a benign cause. Local pathways may use other tools such as the Canadian Syncope Risk Score.
When does it not apply?
It is for transient loss of consciousness with spontaneous recovery (true syncope), not for persistent altered consciousness, seizure, head injury or intoxication, and not for a clear non-syncopal cause. This is an educational reference, not medical advice.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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