San Francisco Syncope Rule (CHESS): the five criteria and how they count
The San Francisco Syncope Rule counts five criteria, remembered as CHESS: a history of Congestive heart failure, Hematocrit below 30%, an abnormal ECG, Shortness of breath, and Systolic blood pressure below 90 mm Hg. Each present criterion counts 1, for a total of 0 to 5, and the rule is called positive when the count is 1 or more. A person with a hematocrit of 29% and nothing else has a count of 1; at 30% the count is 0.
This page doesn't give disposition advice. It shows how the five criteria are counted. What to do with a positive or negative rule depends on the clinical context.
Not a medical device. Not a diagnosis or dosing recommendation.
What is the San Francisco Syncope Rule?
The San Francisco Syncope Rule (SFSR) was published by James V. Quinn, Ian G. Stiell and colleagues in Annals of Emergency Medicine in 2004. It's also called the CHESS rule or CHESS syncope, after its five criteria, or the Quinn syncope rule.
Syncope means fainting: a brief loss of consciousness. The 2004 abstract says the authors set out to "derive a decision rule that would predict patients at risk for short-term serious outcomes."
The rule's own definition is that any one criterion makes it positive, so Magent's calculator returns both the count and that positive/negative flag. This page explains how both are worked out. It doesn't say what a positive rule means for a particular patient.
The CHESS formula
count = chf
+ (hematocrit_percent < 30 ? 1 : 0)
+ abnormal_ecg
+ shortness_of_breath
+ (systolic_bp_mm_hg < 90 ? 1 : 0)
rule positive = count >= 1Exact expression the calculator uses:
CHESS = chf + hematocrit_lt_30 + abnormal_ecg + shortness_of_breath + systolic_bp_lt_90; rule-positive if score ≥ 1; max 5Maximum count: 5.
The five criteria
| Letter | Criterion | Input | Counts 1 when |
|---|---|---|---|
| C | History of congestive heart failure | chf (true/false) | true |
| H | Hematocrit below 30% | hematocrit_percent (10–70) | under 30; 30 doesn't count |
| E | Abnormal ECG | abnormal_ecg (true/false) | true |
| S | Shortness of breath | shortness_of_breath (true/false) | true |
| S | Systolic blood pressure below 90 mm Hg | systolic_bp_mm_hg (50–250) | under 90; 90 doesn't count |
How to apply the rule
- C: history of congestive heart failure? Yes counts 1.
- H: hematocrit under 30%? 29 counts; 30 doesn't.
- E: abnormal ECG? The caller decides; Magent doesn't read ECG tracings.
- S: shortness of breath? Yes counts 1.
- S: systolic pressure under 90 mm Hg? 89 counts; 90 doesn't.
- Add. The count is 0 to 5. A count of 1 or more makes the rule positive.
Both numeric criteria are strict: "below," not "at or below."
What the calculator returns
Magent's calculator returns the count, the maximum of 5, the true/false rule-positive flag, the hematocrit and systolic values it used, and a line for each criterion.
Worked examples
These use Magent's own expected values for the calculator. Unless stated, the yes/no criteria are absent, hematocrit is 40% and systolic pressure is 120 mm Hg.
Example 1: nothing present
- No CHF; hematocrit 40 (not under 30); ECG not abnormal; no shortness of breath; systolic 120 (not under 90).
- Count 0; rule negative.
Example 2: history of CHF alone
- CHF → 1.
- Count 1; rule positive.
Example 3: hematocrit 29 vs 30
- Hematocrit 29 → 1: count 1, rule positive.
- Hematocrit 30 → 0: count 0, rule negative.
Example 4: systolic 89 vs 90
- Systolic 89 → 1: count 1, rule positive.
- Systolic 90 → 0: count 0, rule negative.
Example 5: all five
- CHF → 1; hematocrit 29 → 1; abnormal ECG → 1; shortness of breath → 1; systolic 89 → 1.
- Count 5; rule positive.
San Francisco Syncope Rule reference table
Each row is one of Magent's expected values for the calculator.
| CHF | Hct % | Abnormal ECG | Short of breath | SBP | Count | Rule positive? |
|---|---|---|---|---|---|---|
| No | 40 | No | No | 120 | 0 | No |
| Yes | 40 | No | No | 120 | 1 | Yes |
| No | 29 | No | No | 120 | 1 | Yes |
| No | 30 | No | No | 120 | 0 | No |
| No | 40 | Yes | No | 120 | 1 | Yes |
| No | 40 | No | Yes | 120 | 1 | Yes |
| No | 40 | No | No | 89 | 1 | Yes |
| No | 40 | No | No | 90 | 0 | No |
| Yes | 29 | Yes | Yes | 89 | 5 | Yes |
History of the San Francisco Syncope Rule
The rule comes from James V. Quinn, Ian G. Stiell, Daniel A. McDermott, Karen L. Sellers, Michael A. Kohn and George A. Wells, Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes, Annals of Emergency Medicine, 2004 (volume 43, issue 2, pages 224–232).
The abstract notes that "The causes of syncope are usually benign but are occasionally associated with significant morbidity and mortality." The study was "conducted at a university teaching hospital and used emergency department (ED) patients presenting with syncope or near syncope," with physicians completing a structured data form at the time of the visit.
The study defined serious outcomes in advance as "death, myocardial infarction, arrhythmia, pulmonary embolism, stroke, subarachnoid hemorrhage, significant hemorrhage, or any condition causing a return ED visit and hospitalization for a related event," followed up over 7 days. There were 684 visits for syncope, and 50 predictor variables were considered.
The resulting rule "considers patients with an abnormal ECG, a complaint of shortness of breath, hematocrit less than 30%, systolic blood pressure less than 90 mm Hg, or a history of congestive heart failure." Those are the five criteria and the same strict lines Magent's calculator uses.
When it's used
The 2004 study covered emergency department patients with syncope or near syncope. Magent's record describes the derivation cohort the same way.
Where it's used
The original study took place at a single university teaching hospital.
Who uses it
In the 2004 study, emergency physicians recorded the findings on a structured form while evaluating each patient.
Limits of the calculation
- It counts five criteria. It doesn't examine anyone, doesn't find the cause of a faint and doesn't diagnose anything.
- "Abnormal ECG" is the caller's call. Magent doesn't interpret ECGs.
- The hematocrit and blood-pressure lines are fixed: under 30% and under 90 mm Hg.
- This page doesn't say what to do when the rule is positive or negative.
Clinical decisions belong to a qualified clinician who knows the patient.
How it differs from related calculators
- Canadian CT Head Rule shares two authors (Ian Stiell and George Wells) and also uses yes/no findings, but for minor head injury rather than fainting.
- Ottawa ankle rule is another Stiell-group rule, combining examination findings after an ankle injury.
Glossary
- Syncope: fainting; a brief loss of consciousness with full recovery.
- Near syncope: nearly fainting.
- Hematocrit: the percentage of blood volume made up of red blood cells.
- ECG: electrocardiogram, a recording of the heart's electrical activity.
- Congestive heart failure (CHF): a condition where the heart doesn't pump well enough for the body's needs.
Common mistakes
- Counting a hematocrit of 30%. It has to be below 30.
- Counting a systolic of 90. It has to be below 90.
- Mixing up the two S's. One is Shortness of breath; the other is Systolic blood pressure.
- Treating the count as a scale. The rule's own definition is positive at 1 or more; this page doesn't attach meaning to higher counts.
Source
Quinn JV, Stiell IG, McDermott DA, Sellers KL, Kohn MA, Wells GA. Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes. Ann Emerg Med. 2004;43(2):224-232. DOI: 10.1016/S0196-0644(03)00823-0
Frequently asked questions
What does CHESS stand for?
Congestive heart failure history, Hematocrit below 30%, abnormal ECG, Shortness of breath, and Systolic blood pressure below 90 mm Hg.
How is the San Francisco Syncope Rule calculated?
Count the CHESS criteria that are present. The count runs 0 to 5, and the rule is positive at 1 or more.
What does a positive San Francisco Syncope Rule mean?
At least one CHESS criterion is present. This page doesn't give disposition advice about what follows.
Does a hematocrit of exactly 30% count?
No. The criterion is below 30%.
Who developed the San Francisco Syncope Rule?
James Quinn, Ian Stiell and colleagues, in a 2004 paper in Annals of Emergency Medicine.