SIRS Criteria

What This Calculator Measures

Identifies the systemic inflammatory response syndrome by counting how many of four physiologic criteria are met.

How to Use

1. Enter the patient's temperature, heart rate, respiratory rate, and white blood cell count.
2. Each criterion outside the normal band scores 1 point.
3. Two or more criteria indicate SIRS.
4. Combine with a suspected infection source to consider sepsis.

How the Calculation Works

SIRS counts how many of four criteria are met: temperature above 38 C or below 36 C, heart rate above 90 bpm, respiratory rate above 20 breaths/min, and white blood cell count above 12 or below 4 x10^9/L. Two or more criteria indicate SIRS.

Variables Explained

Interpretation Guide

0–1 criteria: SIRS not met. 2 or more criteria: SIRS present. SIRS plus infection is consistent with the historical definition of sepsis; Sepsis-3 now requires organ dysfunction (SOFA increase ≥2).

Clinical Significance

SIRS criteria have historically underpinned the early recognition and management of sepsis and remain a useful bedside screening framework.

When It Is Useful

• Early recognition of the inflammatory response in undifferentiated illness
• Screening for sepsis in the emergency department
• Teaching and audit of the historical sepsis definitions

When It Is Not Useful

• As the sole definition of sepsis — Sepsis-3 requires organ dysfunction
• In isolation, without clinical assessment for a source of infection

Common Mistakes

• Using SIRS criteria alone to diagnose sepsis without confirming a suspected infection and organ dysfunction.
• Counting a temperature of exactly 38 C as meeting the fever criterion, which requires a value above 38 C or below 36 C.
• Ignoring band forms above 10 percent when the white cell count is otherwise normal, although the band criterion alone can satisfy that item.

Limitations

• SIRS is non-specific and is met in many non-infectious conditions (trauma, pancreatitis, surgery).
• The Sepsis-3 consensus removed SIRS from the formal sepsis definition.
• Physiologic values can be masked by beta-blockade, antipyretics, or immunosuppression.

Worked Example

A patient has temperature 38.5 °C, heart rate 110 bpm, respiratory rate 22/min, and WBC 14 ×10⁹/L.

Expected Result: SIRS present — 4/4 criteria met. Evaluate for infection and consider sepsis workup.

Evidence & References

Source:

SCCM/ESICM Consensus Definitions

Content updated:

2026-08

1. Bone RC, et al. Chest. 1992;101(6):1644-1655.
2. Singer M, et al. JAMA. 2016;315(8):801-810.

References

1. Bone RC, et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Chest. 1992;101(6):1644-1655. (Consensus Definitions)
2. Singer M, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801-810. (Consensus Definition)

Frequently Asked Questions