What are the 4 SIRS criteria?

The four criteria are: (1) Temperature greater than 38°C or less than 36°C, (2) Heart rate greater than 90 beats per minute, (3) Respiratory rate greater than 20 breaths per minute or PaCO2 less than 32 mmHg, and (4) White blood cell count greater than 12,000/mm³, less than 4,000/mm³, or greater than 10% band forms.

How many criteria are needed for a SIRS diagnosis?

A patient is considered SIRS positive when 2 or more of the 4 criteria are met. All 4 criteria are required to be evaluated, but only 2 need to be abnormal.

Is SIRS the same as sepsis?

No. SIRS is a broader physiologic response that can be triggered by infectious or non-infectious causes (e.g., trauma, burns, pancreatitis). Sepsis, by the Sepsis-3 definition, requires suspected or confirmed infection plus organ dysfunction. SIRS meeting criteria with a suspected infection source warrants sepsis evaluation.

Can SIRS occur without infection?

Yes. Non-infectious causes of SIRS include major trauma, surgery, burns, pancreatitis, autoimmune disease, and ischemia. The SIRS framework itself does not distinguish infectious from non-infectious etiology.

Is SIRS still clinically relevant?

While Sepsis-3 guidelines (2016) moved away from SIRS as the primary sepsis definition due to low specificity, SIRS criteria remain widely used in clinical education, initial triage, and some institutional protocols. They are especially useful as a rapid bedside screening tool.

SIRS Criteria Calculator

Check 4 clinical parameters (temperature, heart rate, respiratory rate, WBC) and determine if the patient meets SIRS criteria (2 or more positive).

SIRS Criteria Assessment

Check each criterion that is abnormal for this patient. SIRS is defined as 2 or more of the 4 criteria being met.

1 Abnormal Temperature

Core temp > 38°C (100.4°F) — fever OR < 36°C (96.8°F) — hypothermia

2 Elevated Heart Rate

Heart rate > 90 beats per minute (tachycardia)

3 Abnormal Respiratory Rate or PaCO2

Respiratory rate > 20 breaths/min (tachypnea) OR PaCO2 < 32 mmHg (hyperventilation)

4 Abnormal White Blood Cell Count

WBC > 12,000/mm³ (leukocytosis) OR WBC < 4,000/mm³ (leukopenia) OR Band forms > 10%

Criteria Met 0 of 4

Not Evaluated

0 criteria Threshold: 2 4 criteria

Vertical line marks the 2-criteria threshold

Awaiting input

Toggle the criteria on the left to evaluate the patient.

Criteria Summary

This tool is for educational and informational purposes only. Clinical decisions must be made by qualified healthcare professionals. SIRS criteria alone do not establish a diagnosis of sepsis or any other condition.

SIRS Criteria Quick Reference

Parameter	Abnormal Value
Temperature	> 38°C or < 36°C
Heart Rate	> 90 bpm
Respiratory Rate / PaCO2	RR > 20/min or PaCO2 < 32 mmHg
WBC Count	> 12,000 or < 4,000/mm³ or > 10% bands

Result: SIRS positive = 2 or more criteria met. Sepsis evaluation is warranted when SIRS is present with suspected or confirmed infection.

Summary

Systemic Inflammatory Response Syndrome (SIRS) is a clinical syndrome defined by 2 or more of 4 measurable physiologic abnormalities: abnormal body temperature, increased heart rate, abnormal respiratory rate or PaCO2, and abnormal white blood cell count. Originally defined at the 1991 ACCP/SCCM Consensus Conference, SIRS criteria serve as an early screening framework for identifying patients at risk of sepsis or organ dysfunction. While largely superseded by Sepsis-3 definitions in critical care, SIRS remains widely taught and used in clinical triage and medical education.

How it works

Review each of the 4 SIRS criteria listed in the tool.
Toggle each criterion that applies to the patient.
The tool instantly counts positive criteria and displays whether the patient meets SIRS definition.
SIRS is positive when 2 or more criteria are met.
Read the clinical interpretation and recommended next steps.

Use cases

Early bedside screening for systemic inflammatory response.
Teaching medical students and residents the SIRS framework.
Triage support in emergency and ICU settings.
Rapid identification of patients who may require sepsis workup.
Clinical decision support for nursing and allied health staff.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu