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SIRS Criteria (Systemic Inflammatory Response Syndrome)

SIRS is present when ≥2 of 4 criteria are met: temperature >38 °C or <36 °C, heart rate >90, respiratory rate >20 or PaCO₂ <32 mmHg, and WBC >12 or <4 ×10⁹/L or >10% bands. SIRS plus suspected infection was the 1992 (Sepsis-1) definition of sepsis.

Temperature (°C or °F)
Heart rate (/min)
Respiratory rate (/min)
PaCO₂ (arterial) (mmHg or kPa)
WBC (×10⁹/L or ×10³/µL)
Bands >10% (yes/no, +1)

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Interpretation

Result	Meaning
0–1	SIRS not present
≥2	SIRS present; with infection = Sepsis-1 "sepsis"

Formula

Count: T >38 or <36 °C · HR >90 · RR >20 or PaCO₂ <32 mmHg · WBC >12 or <4 ×10⁹/L or >10% bands. SIRS = ≥2.

Clinical pearls

Highly sensitive but non-specific: many hospitalized patients without infection meet SIRS.
Sepsis-3 (2016) replaced SIRS with SOFA-based organ dysfunction, but SIRS remains in some quality measures (e.g. SEP-1).

Examples

sirs temp 38.5 hr 100 rr 18 wbc 8 sirs criteria for temperature 101.5 F, pulse 115, resp 24, white count 15 does this patient meet sirs? T 36.5, HR 88, RR 16, WBC 3.2

FAQ

How many SIRS criteria are needed?

Two or more of the four criteria.

Is SIRS still used to define sepsis?

Not under Sepsis-3, which uses an acute SOFA rise of ≥2, but SIRS persists in some screening tools and quality metrics.

Evidence

Bone RC et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis (ACCP/SCCM Consensus Conference). Chest 1992;101:1644–55.

Pulmonary & Critical Care · Reviewed 2026-10-14 · Methodology