SIRS Criteria Calculator
SIRS Criteria Calculator
Screen for the systemic inflammatory response — four bedside-and-lab criteria that once defined sepsis and are now a screening prompt, not a diagnosis.
SIRS Criteria
4 items → 0–4Temperature abnormal (1), heart rate above 90 (1), respiratory rate above 20 (1), white cell count normal (0)
Scoring
- Temperature
- above 38°C or below 36°C
- Heart rate
- above 90 beats per minute
- Respiratory rate
- above 20 per minute, or PaCO₂ below 32 mmHg
- White cells
- above 12 or below 4 ×10⁹/L, or over 10% immature (band) forms
- SIRS met
- two or more of the four criteria
Worked example
Temperature abnormal (1), heart rate above 90 (1), respiratory rate above 20 (1), white cell count normal (0)
1 + 1 + 1 + 0 = 3 criteria
3 is 2 or more → SIRS met
The four SIRS criteria
| Criterion | Threshold |
|---|---|
| Temperature | > 38°C or < 36°C |
| Heart rate | > 90 per minute |
| Respiratory rate | > 20 per minute, or PaCO₂ < 32 mmHg |
| White cell count | > 12 or < 4 ×10⁹/L, or > 10% bands |
Why SIRS was dropped from the sepsis definition
Systemic inflammatory response syndrome was defined in 1991 as two or more of four criteria — an abnormal temperature, tachycardia, tachypnoea or hypocapnia, and an abnormal white cell count — intended to capture the body’s response to a range of insults, infective and non-infective alike. For two decades it sat at the centre of the sepsis definitions: infection plus SIRS was sepsis, and SIRS plus organ dysfunction was severe sepsis.
Sepsis-3, published in 2016, removed SIRS from the definition entirely, and it is worth being candid about why. SIRS is met by almost anyone with a fever and a fast pulse — after exercise, after surgery, during a minor viral illness — so it flags very large numbers of people who are not septic. At the same time it is insensitive: roughly one in eight patients with infection and confirmed organ dysfunction never meet two SIRS criteria, often because they are elderly, immunosuppressed, or on a rate-limiting drug. A screen that both over-calls and under-calls this badly does not discriminate well.
Sepsis is now defined as suspected infection together with an acute rise in the SOFA score of 2 points or more, which correlates far better with outcome. SIRS survives in two places: as a rapid bedside prompt in some early-warning protocols, where cheap sensitivity still has a role, and throughout older literature, quality metrics and coding systems built around the 1991 definitions that have not all been rewritten. Treat a positive score as a prompt to look further, never as a diagnosis of sepsis on its own.
Frequently asked questions
What SIRS score means the criteria are met?
Two or more of the four criteria — abnormal temperature, heart rate, respiratory rate and white cell count. Each is worth one point, out of a maximum of four.
Is SIRS the same as sepsis?
No. Sepsis-3 (2016) removed SIRS from the definition of sepsis, which is now suspected infection plus an acute rise in SOFA of 2 or more. SIRS can be present without infection, and sepsis can be present without meeting SIRS.
Why was SIRS removed from the sepsis definition?
It is too non-specific — met by anyone with a fever and tachycardia, including after exercise or a minor illness — and too insensitive, missing roughly one in eight patients with confirmed infection and organ dysfunction.
Is SIRS still useful for anything?
It persists as a rapid, low-cost bedside screening prompt in some protocols, and it remains embedded in older literature, quality metrics and coding systems built around the pre-2016 definitions.
Related calculators
References
- Bone RC et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Chest. 1992;101(6):1644–55.
- Singer M et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801–10.