This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
What is SIRS?
The systemic inflammatory response syndrome (SIRS) describes the body’s general reaction to a serious insult, infectious or not. It was defined at a 1991 consensus conference of the American College of Chest Physicians and the Society of Critical Care Medicine, together with the first definitions of sepsis, severe sepsis and septic shock.
The four criteria
| Criterion | Threshold |
|---|---|
| temperature | above 38 °C (100.4 °F) or below 36 °C (96.8 °F) |
| heart rate | above 90 beats per minute |
| breathing | respiratory rate above 20 per minute, or PaCO₂ below 32 mmHg |
| white blood cells | above 12 × 10⁹/L, below 4 × 10⁹/L, or more than 10% immature (band) forms |
SIRS is present when at least 2 of the 4 criteria are met.
From SIRS to sepsis
Under the 1991 definitions, SIRS due to a confirmed or suspected infection was sepsis; sepsis with organ dysfunction was severe sepsis; and sepsis with persistent low blood pressure despite fluids was septic shock.
In 2016, the Third International Consensus (Sepsis-3) changed this. Because many patients with ordinary infections meet SIRS criteria, and some patients with severe sepsis do not, sepsis is now defined as life-threatening organ dysfunction caused by a dysregulated response to infection, identified by a rise of 2 points or more in the SOFA score. The quick SOFA (qSOFA) was proposed as a bedside prompt.
Example
A patient with a temperature of 101.5 °F (38.6 °C), a heart rate of 104, a respiratory rate of 18 and 13,500 white cells meets 3 criteria. With a suspected urinary infection, they had sepsis under the old definition. Today, the next step is to look for organ dysfunction: blood pressure, mental status, oxygen, kidney function, platelets, bilirubin and lactate.
Why SIRS is still useful
- It is highly sensitive and quick, so it remains a common screening tool in emergency departments and on wards.
- US hospital quality measures for sepsis care still use SIRS criteria.
- It applies to non-infectious causes such as pancreatitis, burns, trauma and major surgery.
Limits
SIRS is not specific: exercise, pain, anxiety and many minor illnesses can produce two criteria. It should prompt clinical assessment, never replace it. Early antibiotics and fluids remain the key to treating sepsis.