SIRS Criteria Calculator: SIRS, Sepsis, Severe Sepsis and Septic Shock
Count the 4 SIRS criteria (temperature, heart rate, respiratory rate or PaCO₂, white cell count or bands) in °C or °F, then check sepsis, severe sepsis and septic shock with the SEP-1 organ-dysfunction list, plus qSOFA and the Sepsis-3 shock criteria.
How it works
SIRS = 2 or more of: temperature > 38 °C (100.4 °F) or < 36 °C (96.8 °F); heart rate > 90/min; respiratory rate > 20/min or PaCO₂ < 32 mmHg; WBC > 12 or < 4 ×10⁹/L or > 10% bands. Sepsis = SIRS + infection. Severe sepsis = sepsis + any organ dysfunction sign (SBP < 90, MAP < 65, SBP fall > 40, lactate > 2, creatinine > 2.0, bilirubin > 2, platelets < 100, INR > 1.5, new ventilation). Septic shock = hypotension after 30 mL/kg fluid or lactate ≥ 4. qSOFA = RR ≥ 22 + SBP ≤ 100 + altered mentation.
The 1992 ACCP/SCCM consensus (confirmed in 2001) defined the systemic inflammatory response syndrome as two or more of four abnormalities: temperature, heart rate, breathing (rate or arterial PaCO₂) and the white cell count, including more than 10% immature band forms. Sepsis was SIRS caused by infection, severe sepsis was sepsis with organ dysfunction, hypotension or hypoperfusion, and septic shock was hypotension that persists despite adequate fluid. This calculator counts the four criteria, shows which ones are met, and, if you switch on the organ check, applies the organ-dysfunction list used by the US SEP-1 quality measure, where a lactate of 4 mmol/L or more also counts as shock. The criteria are sensitive but not specific: exercise, pain, surgery, burns or pancreatitis can all meet them without infection, and a large ICU study found that about 1 in 8 infected patients with new organ failure had fewer than two criteria. For that reason the 2016 Sepsis-3 definitions replaced SIRS with organ dysfunction (an acute SOFA rise of 2 or more) and defined septic shock as needing vasopressors to keep MAP at 65 mmHg or more with lactate above 2 mmol/L after fluids. The calculator also gives the qSOFA bedside score (respiratory rate 22 or more, systolic pressure 100 or less, altered mentation), which flags infected patients at higher risk. SIRS remains part of many hospital screening tools because it needs only vital signs and a blood count. The thresholds are for adults.
Worked example
Default patient: temperature 38.4 °C (101.1 °F) → 1; heart rate 96 → 1; respiratory rate 22 → 1; white cells 13.2 ×10⁹/L with 5% bands → 1. SIRS 1 + 1 + 1 + 1 = 4 of 4, so SIRS is present; with infection marked No the result suggests other causes of SIRS. qSOFA: respiratory rate 22 scores 1, systolic 118 scores 0, normal mentation 0, so qSOFA is 1 of 3. MAP = (118 + 2 × 74) ÷ 3 = 89 mmHg. Mark infection Yes and the result becomes sepsis by the 1992/2001 definition; switch on the organ check with a lactate of 4.2 mmol/L and it becomes septic shock by SEP-1.
Sources: Guideline Central: SIRS, sepsis and septic shock criteria · WikEM: SIRS criteria · Norton Healthcare: severe sepsis and septic shock criteria (CMS SEP-1) · Sepsis-3 definitions and qSOFA, summary · Kaukonen et al. 2015 (SIRS-negative severe sepsis), journal club summary
Frequently asked questions
What are the 4 SIRS criteria?
Temperature above 38 °C (100.4 °F) or below 36 °C (96.8 °F); heart rate above 90 per minute; respiratory rate above 20 per minute or PaCO₂ below 32 mmHg; and a white cell count above 12,000 or below 4,000 per µL, or more than 10% bands. Two or more means SIRS.
Is SIRS the same as sepsis?
No. Under the 1992/2001 definitions sepsis is SIRS caused by a suspected or confirmed infection. SIRS without infection is common after surgery, trauma, burns or pancreatitis. Under Sepsis-3 sepsis is infection with new organ dysfunction, whatever the SIRS count.
Why does SIRS still matter if Sepsis-3 replaced it?
Because it is sensitive and needs only vital signs and a blood count. Many hospital screening tools and the US SEP-1 measure still use SIRS to start a sepsis work-up, and the diagnosis is then confirmed with organ-function tests such as SOFA and lactate.
What is the difference between SIRS and qSOFA?
SIRS counts inflammation signs and is sensitive but not specific. qSOFA (respiratory rate 22 or more, systolic pressure 100 or less, altered mentation) predicts a poor outcome in infected patients better but misses many early cases, so neither is a stand-alone test.
What counts as septic shock?
In SEP-1 and the older definitions: severe sepsis with hypotension that persists after 30 mL/kg of crystalloid, or a lactate of 4 mmol/L or more. In Sepsis-3: vasopressors needed to keep MAP at 65 mmHg or more and lactate above 2 mmol/L despite adequate fluids.
Are the criteria different in children?
Yes. Paediatric SIRS uses age-specific heart rate, breathing and white cell limits, and one of the two criteria must be abnormal temperature or white cell count. This calculator uses the adult thresholds.
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Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.