SIRS Criteria — Systemic Inflammatory Response Syndrome
The Systemic Inflammatory Response Syndrome (SIRS) criteria are a set of four physiological parameters used to identify patients with systemic inflammation. The presence of two or more criteria suggests SIRS and should prompt evaluation for underlying infection or other causes.
About
The SIRS criteria were established at the 1991 American College of Chest Physicians/Society of Critical Care Medicine (ACCP/SCCM) Consensus Conference to define the systemic inflammatory response to infection and other insults. The four criteria are: (1) Temperature <36°C or >38°C, (2) Heart rate >90 bpm, (3) Respiratory rate >20 breaths/min or PaCO2 <32 mmHg, (4) White blood cell count >12,000/mm³ or <4,000/mm³ or >10% bands. While SIRS criteria are sensitive for detecting inflammation, they lack specificity. The Sepsis-3 definition (2016) shifted towards using qSOFA for sepsis screening, but SIRS remains in clinical use and in the CMS SEP-1 core measure.
Formula
SIRS score = (Temp<36°C or >38°C) + (HR>90) + (RR>20 or PaCO2<32) + (WBC>12K or <4K or >10% bands). Score 0-4.
SIRS is diagnosed when ≥2 of 4 criteria are present: Temperature <36°C or >38°C (abnormal temperature), Heart rate >90 bpm (tachycardia), Respiratory rate >20/min or PaCO2 <32 mmHg (tachypnea or hypocapnia), WBC >12,000/mm³ or <4,000/mm³ or >10% immature neutrophils (bands).
Score Interpretation
SIRS criteria remain clinically important despite the Sepsis-3 shift to qSOFA. CMS SEP-1 core measure still uses SIRS for severe sepsis identification. SIRS has high sensitivity (72-100%) but low specificity (43-80%) for sepsis diagnosis.
SIRS Not Met — 0–1
<2 criteria present. Systemic inflammation unlikely.
Management: Continue monitoring. Reassess if clinical condition changes.
SIRS Met — 2+
≥2 criteria present. SIRS is present.
Management: Investigate for infection (cultures, imaging). Start empiric antibiotics if infection suspected. Check lactate for tissue hypoperfusion.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| All patients with suspected infection or inflammation | 0-4 criteria met | ≥2 criteria = SIRS present |
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Expert critical care review panel.
View medical review board & editorial policy →Example Calculation
A patient with pneumonia: Temp 38.5°C (1), HR 105 (1), RR 22 (1), WBC 14.5K (1). SIRS score = 4. All four criteria met.
Related Conditions
Related Medications
Common Mistakes
Using SIRS alone to diagnose sepsis without assessing organ dysfunction.
Sepsis requires both SIRS (or qSOFA) criteria AND evidence of organ dysfunction. SIRS alone indicates systemic inflammation.
Frequently Asked Questions
Is SIRS still relevant after Sepsis-3?
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.