SIRS (Systemic Inflammatory Response Syndrome) is defined by ≥2 of 4 criteria: temperature >38°C or <36°C, HR >90 bpm, RR >20 or PaCO₂ <32 mmHg, WBC >12,000 or <4,000 or >10% bands. It represents a systemic inflammatory response from any cause — infection, trauma, burns, surgery, pancreatitis, or autoimmune disease.

Is SIRS still used in sepsis diagnosis?

The Sepsis-3 definition (2016) replaced SIRS with SOFA ≥2 for clinical sepsis diagnosis. However, SIRS remains required for CMS SEP-1 quality reporting. Many hospitals run dual protocols: SIRS for regulatory compliance and qSOFA/SOFA for clinical practice.

What are the limitations of SIRS?

SIRS has ~90% sensitivity for bacteremia but only ~50% specificity — up to 50% of hospitalized patients meet SIRS criteria without infection. This poor specificity was why Sepsis-3 moved to SOFA-based criteria. SIRS alone cannot distinguish infectious from non-infectious systemic inflammation.

What are the 4 SIRS criteria?

Temperature >38°C or <36°C; Heart rate >90 bpm; Respiratory rate >20 breaths/min OR PaCO₂ <32 mmHg; WBC >12,000/mm³ OR <4,000/mm³ OR >10% band forms. SIRS is present when ≥2 criteria are met.

What non-infectious conditions cause SIRS?

Non-infectious SIRS causes include: trauma, major surgery, burns, acute pancreatitis, myocardial infarction, pulmonary embolism, autoimmune disease, adrenal crisis, thyroid storm, heat stroke, severe anemia, and drug reactions. SIRS is a non-specific systemic alarm signal.

What is the difference between SIRS and sepsis?

Historically, SIRS + infection = sepsis. Under Sepsis-3: sepsis = infection + SOFA ≥2 (organ dysfunction). A patient can have SIRS without infection (trauma, pancreatitis) — this is not sepsis. A patient can have sepsis without meeting SIRS criteria (e.g., hypothermic elderly patient). SIRS is a broader signal; sepsis requires infection + organ dysfunction.

How does SIRS relate to pancreatitis severity?

In acute pancreatitis, persistent SIRS (>48 hours) strongly predicts necrotizing pancreatitis, organ failure, and mortality. Transient SIRS (<48h) generally indicates mild pancreatitis. The revised Atlanta Classification (2012) incorporates SIRS as a key prognostic variable.

Should I start antibiotics based on SIRS criteria alone?

No. Antibiotics should be started based on clinical suspicion of infection + SIRS criteria, not SIRS alone. A patient with SIRS from post-operative inflammation, pancreatitis, or trauma should NOT receive empiric antibiotics without clinical evidence of infection.

What is CMS SEP-1 and why does it use SIRS?

CMS SEP-1 (Severe Sepsis and Septic Shock: Management Bundle) is a hospital quality measure that still uses SIRS + infection as its trigger, as it was created before Sepsis-3. Hospitals must document SIRS-based sepsis recognition for CMS compliance even though Sepsis-3 defines sepsis differently.

Do bands alone satisfy the WBC SIRS criterion?

Yes. Bands >10% alone satisfy the WBC SIRS criterion, regardless of total WBC. A patient with WBC 8,000 but 15% bands meets the criterion. Always check the WBC differential, not just the total count, when evaluating SIRS.

Can elderly patients fail to show SIRS criteria despite serious infection?

Yes. Elderly and immunocompromised patients may have blunted fever responses (or hypothermia), leukopenia instead of leukocytosis, and blunted tachycardia (on beta-blockers). These patients may have severe sepsis with only 0–1 SIRS criteria. Always apply clinical judgment — an elderly confused patient with suspected infection warrants sepsis workup regardless of SIRS count.

What is the temperature threshold for SIRS?

SIRS temperature criterion: >38°C (100.4°F) OR <36°C (96.8°F). Temperatures between 36°C and 38°C are considered normal for SIRS purposes. Axillary temperatures typically run 0.5–1°C lower than core — confirm oral or rectal/tympanic temperature when possible for accurate SIRS scoring.

Online Medical Tools — SIRS Criteria

Printed on 8/14/2026

For informational purposes only. This is not medical advice.

Emergency

SIRS Criteria

The Systemic Inflammatory Response Syndrome (SIRS) criteria were defined in 1992 as a set of four clinical findings that indicate a generalized inflammatory process. SIRS is present when two or more criteria are met: temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >20 or PaCO₂ <32 mmHg, and WBC >12,000 or <4,000 or >10% bands. While Sepsis-3 (2016) moved to SOFA-based definitions, SIRS criteria remain widely referenced and used in many clinical settings for early identification of inflammatory states. For Sepsis-3 diagnosis, use qSOFA Score (bedside) and SOFA Score (full). Assess severity with APACHE II. Track organ perfusion with MAP Calculator. Pneumonia is the most common cause of sepsis — assess with CURB-65.

Formula: SIRS = sum of 4 criteria (each 0 or 1). SIRS positive ≥ 2.

Temperature >38°C (100.4°F) or <36°C (96.8°F)

Heart rate >90 bpm

Respiratory rate >20 or PaCO₂ <32 mmHg

WBC >12,000 or <4,000 or >10% bands

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How It Works

Assess 4 physiological variables

Evaluate four criteria: (1) Temperature: >38°C or <36°C. (2) Heart rate: >90 bpm. (3) Respiratory rate: >20 breaths/min OR PaCO₂ <32 mmHg. (4) WBC: >12,000/mm³ or <4,000/mm³ or >10% immature band forms. Each criterion is binary. SIRS can be assessed with temperature, HR, and RR before WBC is available.

Determine if SIRS is present (≥2 criteria)

SIRS is present if 2 or more of the 4 criteria are met. The number of SIRS criteria met (2, 3, or 4) provides additional prognostic value — more criteria generally indicate more severe systemic inflammation. However, even 4/4 SIRS criteria does not establish sepsis without a suspected or confirmed infection source.

Combine with clinical context to determine next steps

SIRS + suspected infection: initiate sepsis workup (blood cultures, lactate, CBC/CMP, antibiotics) and calculate [qSOFA](/tools/qsofa) and [SOFA Score](/tools/sofa-score) for Sepsis-3 organ dysfunction assessment. SIRS without infection: evaluate for non-infectious causes (trauma, burns, pancreatitis, MI, PE, autoimmune). For CMS SEP-1 reporting, document SIRS recognition time as the sepsis bundle clock start.

Who Uses the SIRS Criteria

CMS/TJC Sepsis Quality Reporting (SEP-1 Bundle Trigger)

Quality officers, hospitalists, ED physicians

The CMS SEP-1 quality measure still uses SIRS criteria + infection as the bundle trigger for regulatory reporting, despite Sepsis-3 replacing SIRS for clinical diagnosis. Hospitals must identify SIRS-based sepsis for CMS documentation. Track time of SIRS recognition as the 'sepsis clock' for SEP-1 compliance even while using qSOFA/SOFA clinically.

Early Sepsis Identification in ED and Wards

Emergency physicians, ward nurses, triage staff

Despite being replaced by Sepsis-3 for clinical diagnosis, SIRS retains approximately 90% sensitivity for bacteremia. SIRS + suspected infection should prompt blood cultures, lactate, and antibiotic consideration. Many hospital EHR-based sepsis alert systems still use SIRS as the trigger. Use alongside [qSOFA](/tools/qsofa) for dual-protocol approaches.

Pancreatitis Severity Assessment

Gastroenterologists, general surgeons, hospitalists

SIRS presence in acute pancreatitis predicts severity: SIRS in the first 48 hours correlates with pancreatic necrosis and organ failure (Banks et al., revised Atlanta Classification 2012). Persistent SIRS (>48 hours) is the strongest predictor of severe acute pancreatitis requiring ICU-level care. Early aggressive fluid resuscitation in SIRS-positive pancreatitis improves outcomes.

Post-Surgical Inflammatory Assessment

Surgeons, post-operative nursing, hospitalists

SIRS is nearly universal in the first 24–48 hours after major surgery. The clinical challenge is distinguishing post-operative physiologic SIRS from early surgical site infection, anastomotic leak, or pneumonia. Serial SIRS assessment beyond post-operative day 2 is more clinically meaningful than early post-op SIRS.

Trauma and Burns Systemic Response Monitoring

Trauma surgeons, burn centers, ICU teams

Major trauma and extensive burns reliably trigger SIRS through non-infectious mechanisms (cytokine storm, tissue necrosis, reperfusion injury). Differentiating SIRS from developing infection requires serial clinical assessment, cultures, and procalcitonin. SIRS scores in trauma correlate with injury severity and predict ICU length of stay and organ dysfunction.

Historical Sepsis Research Interpretation

Clinical researchers, medical educators

An enormous body of sepsis literature uses SIRS-based definitions (pre-2016). Understanding SIRS criteria is essential for interpreting historical sepsis trials (PROWESS, CORTICUS, ProCESS, ARISE). SIRS-defined 'sepsis' in older studies includes a broader population than Sepsis-3 SOFA-defined sepsis. Apply appropriate interpretation when translating research findings to practice.

Pro Tips

Sepsis-3 (2016) replaced SIRS as the clinical sepsis definition — use SOFA instead

The Sepsis-3 task force abandoned SIRS as the sepsis definition due to its poor specificity (~50%). Sepsis-3 defines sepsis as suspected infection + SOFA ≥2. Clinically, use [qSOFA](/tools/qsofa) for bedside screening and [SOFA Score](/tools/sofa-score) for formal organ dysfunction quantification. Know SIRS for regulatory compliance and historical context.

CMS SEP-1 still uses SIRS — regulatory and clinical definitions differ

CMS SEP-1 uses SIRS + infection as its trigger, despite Sepsis-3 replacing this clinically. Hospitals must document SIRS-based sepsis recognition for CMS compliance even when following Sepsis-3 clinically. Implement dual-protocol documentation: SIRS-based for CMS, qSOFA/SOFA-based for clinical practice.

SIRS in pancreatitis: persistent SIRS >48h predicts severe disease

In acute pancreatitis, transient SIRS (<48h) indicates mild-moderate disease; persistent SIRS (>48h) strongly predicts necrotizing pancreatitis and organ failure. The revised Atlanta Classification (2012) incorporates organ failure to define severe acute pancreatitis. Early aggressive fluid resuscitation (250–500 mL/h Lactated Ringer's) in SIRS-positive pancreatitis improves outcomes.

Bands >10% (left shift) reflects bone marrow response to severe infection

Immature neutrophils (bands) >10% indicate early bone marrow release under infectious stress. This is more specific for infection than total WBC elevation alone. Many automated CBC analyzers may not reliably count bands — manual differential may be needed. Bands >10% add meaningful specificity to the WBC criterion.

SIRS has ~90% sensitivity for bacteremia — useful as a broad-net screen

SIRS ≥2 criteria has approximately 90% sensitivity for bacteremia. A patient who does NOT meet SIRS criteria is unlikely to have bacteremia. However, 50% specificity means half of SIRS-positive patients don't have infection. Use SIRS to cast a wide net, then use clinical judgment and further workup to narrow the differential.

Non-infectious SIRS triggers: know the full differential

SIRS occurs with: MI, PE, trauma, burns, major surgery, pancreatitis, autoimmune disease, adrenal insufficiency, thyroid storm, heat stroke, and severe anemia. When SIRS is present without an obvious infection source, consider these diagnoses before reflexively starting antibiotics.

Temperature criteria: both fever AND hypothermia count

SIRS temperature criterion: >38°C (fever) OR <36°C (hypothermia). Hypothermia in sepsis is ominous — it may indicate overwhelming infection, gram-negative bacteremia, or immunosuppression. Hypothermic SIRS patients should be treated with the same urgency as febrile patients, if not more so.

WBC criterion: check the differential, not just total WBC

The WBC criterion is positive if total WBC >12,000, <4,000, OR bands >10% regardless of total WBC. A patient with WBC 8,000 but 15% bands meets the WBC criterion. Always review the WBC differential when evaluating SIRS.

Common Questions About Your Results

No. SIRS criteria alone do not indicate infection — they indicate systemic inflammation from any cause. Antibiotics should be started based on clinical assessment of suspected infection plus SIRS criteria, not SIRS alone. A post-operative patient 24 hours after bowel surgery who is tachycardic with mild fever likely has physiologic post-operative inflammation. Use clinical judgment, not just SIRS numbers.

Evidence-Based Methodology

SIRS criteria defined by the ACCP/SCCM Consensus Conference (Bone et al., Chest 1992). SIRS as sepsis definition replaced by Sepsis-3 (Singer et al., JAMA 2016) based on poor specificity of SIRS for predicting infection-related organ dysfunction. CMS/TJC SEP-1 measure still uses SIRS as part of the trigger (Dellinger, Crit Care Med 2014 reporting infrastructure). SIRS sensitivity for bacteremia ~90%, specificity ~50%. SIRS in pancreatitis severity: Banks and Freeman (Am J Gastroenterol 2006 Atlanta Criteria revision).

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

Your result indicates whether the Systemic Inflammatory Response Syndrome (SIRS) criteria are met. Meeting two or more of the four criteria (abnormal temperature, tachycardia, tachypnea or low PaCO2, abnormal WBC) defines SIRS-positive status. A SIRS-positive result indicates that the body is mounting a systemic inflammatory response, which may be due to infection (sepsis), trauma, burns, pancreatitis, surgery, or other inflammatory conditions.

A SIRS-negative result (0–1 criteria met) suggests the patient does not currently display a generalized inflammatory response, though this does not rule out localized infection or early systemic disease. Serial reassessment is important because SIRS status can change rapidly as the clinical picture evolves.

When to Use This Tool

Use the SIRS criteria as a bedside screening tool for early identification of systemic inflammation in acutely ill patients. It is most commonly applied in the emergency department, surgical settings, and inpatient wards when evaluating patients with suspected infection, post-operative fever, trauma, or other conditions that may trigger a systemic inflammatory response.

Although the Sepsis-3 definition (2016) moved toward SOFA-based criteria for defining sepsis, SIRS criteria remain valuable for initial screening, particularly in settings where laboratory values for SOFA are not immediately available. Many hospitals still use SIRS-based screening protocols as part of sepsis alert systems. The criteria are also widely used in clinical research and as inclusion criteria for clinical trials.

Limitations

SIRS criteria are highly sensitive but poorly specific for infection. Up to 50% of hospitalized patients — particularly post-surgical patients, trauma patients, and those in the ICU — may meet SIRS criteria without having an infection. This high false-positive rate was a major reason the Sepsis-3 task force moved to SOFA-based definitions for sepsis.

Conversely, some patients with serious infections (particularly elderly or immunocompromised patients) may not mount a SIRS response, leading to false negatives. The criteria also do not differentiate between infectious and non-infectious causes of inflammation. For sepsis-specific screening, qSOFA or the full SOFA score may provide better specificity. SIRS criteria should always be interpreted alongside clinical context, not used as a standalone diagnostic tool.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.

Changelog

April 21, 2026 · trust-baseline
Clinical trust metadata enabled for this tool page with structured review/version fields.

Related Tools

Emergency

Online Medical Tools — SIRS Criteria

SIRS Criteria

How It Works

Assess 4 physiological variables

Determine if SIRS is present (≥2 criteria)

Combine with clinical context to determine next steps

Who Uses the SIRS Criteria

CMS/TJC Sepsis Quality Reporting (SEP-1 Bundle Trigger)

Early Sepsis Identification in ED and Wards

Pancreatitis Severity Assessment

Post-Surgical Inflammatory Assessment

Trauma and Burns Systemic Response Monitoring

Historical Sepsis Research Interpretation

Pro Tips

Sepsis-3 (2016) replaced SIRS as the clinical sepsis definition — use SOFA instead

CMS SEP-1 still uses SIRS — regulatory and clinical definitions differ

SIRS in pancreatitis: persistent SIRS >48h predicts severe disease

Bands >10% (left shift) reflects bone marrow response to severe infection

SIRS has ~90% sensitivity for bacteremia — useful as a broad-net screen

Non-infectious SIRS triggers: know the full differential

Temperature criteria: both fever AND hypothermia count

WBC criterion: check the differential, not just total WBC

Common Questions About Your Results

Evidence-Based Methodology

Clinical Content Trust

How to Interpret Your Result

When to Use This Tool

Limitations

Changelog

Related Tools

qSOFA Score

SOFA Score

Centor Score

Further Reading

A Complete Guide to Emergency Medicine: Decision Tools, Scoring Systems, and Clinical Protocols

Frequently Asked Questions

Online Medical Tools — SIRS Criteria

SIRS Criteria

How It Works

Assess 4 physiological variables

Determine if SIRS is present (≥2 criteria)

Combine with clinical context to determine next steps

Who Uses the SIRS Criteria

CMS/TJC Sepsis Quality Reporting (SEP-1 Bundle Trigger)

Early Sepsis Identification in ED and Wards

Pancreatitis Severity Assessment

Post-Surgical Inflammatory Assessment

Trauma and Burns Systemic Response Monitoring

Historical Sepsis Research Interpretation

Pro Tips

Sepsis-3 (2016) replaced SIRS as the clinical sepsis definition — use SOFA instead

CMS SEP-1 still uses SIRS — regulatory and clinical definitions differ

SIRS in pancreatitis: persistent SIRS &gt;48h predicts severe disease

Bands &gt;10% (left shift) reflects bone marrow response to severe infection

SIRS has ~90% sensitivity for bacteremia — useful as a broad-net screen

Non-infectious SIRS triggers: know the full differential

Temperature criteria: both fever AND hypothermia count

WBC criterion: check the differential, not just total WBC

Common Questions About Your Results

Evidence-Based Methodology

Clinical Content Trust

How to Interpret Your Result

When to Use This Tool

Limitations

Changelog

Related Tools

qSOFA Score

SOFA Score

Centor Score

Further Reading

A Complete Guide to Emergency Medicine: Decision Tools, Scoring Systems, and Clinical Protocols

Frequently Asked Questions

SIRS in pancreatitis: persistent SIRS >48h predicts severe disease

Bands >10% (left shift) reflects bone marrow response to severe infection