SIRS Criteria Calculator
SIRS criteria from temperature, heart rate, respiration, and white blood cell count.
What it does
SIRS stands for systemic inflammatory response syndrome. It is a set of bedside criteria that describe a widespread inflammatory response, whether or not infection is present.
The four criteria are temperature above 38 C or below 36 C, heart rate above 90 beats per minute, respiratory rate above 20 breaths per minute or PaCO2 below 32 mm Hg or mechanical ventilation, and white blood cell count above 12 or below 4 x 10^9/L or bands above 10 percent.
Two or more criteria define SIRS. SIRS is not a diagnosis of sepsis. Current sepsis definitions require a suspected or confirmed infection plus organ dysfunction, and SIRS criteria are no longer part of the Sepsis-3 definition.
The defaults show a temperature of 38.4 C, heart rate 108, respiratory rate 22, and white blood cell count 14.5 x 10^9/L. All four criteria are present, so the result is SIRS positive.
How to use
- Choose Celsius or Fahrenheit for the temperature.
- Enter the temperature, heart rate, respiratory rate, and PaCO2.
- Enter the white blood cell count and band neutrophil percentage.
- Indicate whether the patient is mechanically ventilated.
- Press Calculate to see how many SIRS criteria are present.
- Use the result with the infection assessment and organ dysfunction evaluation; SIRS alone does not define sepsis.
Formula
- Temperature
- Above 38 C (100.4 F) or below 36 C (96.8 F).
- Heart rate
- Above 90 beats/min.
- Respiratory
- Respiratory rate above 20/min, PaCO2 below 32 mm Hg, or mechanical ventilation.
- White blood cells
- Above 12 or below 4 x 10^9/L, or bands above 10 percent.
Count each of the four criteria as present or absent. Two or more positive criteria make SIRS positive. The thresholds are strict, so a temperature of exactly 38 C, a heart rate of exactly 90, or a respiratory rate of exactly 20 does not count. Fahrenheit values are converted to Celsius before applying the temperature threshold.
Worked example
Example: temperature 38.4 C, heart rate 108, respiratory rate 22, WBC 14.5
Defaults: temperature 38.4 C, heart rate 108/min, respiratory rate 22/min, PaCO2 38 mm Hg, WBC 14.5 x 10^9/L, bands 8 percent, not ventilated.
- Temperature 38.4 C is above 38 C: criterion present.
- Heart rate 108 is above 90: criterion present.
- Respiratory rate 22 is above 20: criterion present.
- WBC 14.5 is above 12: criterion present.
- The criteria count is 4, which is 2 or more, so SIRS is positive.
- The tool notes that SIRS alone does not define sepsis; evaluate for infection and organ dysfunction.
Reference table
| Criterion | Positive when |
|---|---|
| Temperature | Above 38 C (100.4 F) or below 36 C (96.8 F) |
| Heart rate | Above 90 beats/min |
| Respiratory | Rate above 20/min, PaCO2 below 32 mm Hg, or mechanical ventilation |
| White blood cells | Above 12 or below 4 x 10^9/L, or bands above 10 percent |
Limits
- SIRS is nonspecific and can occur with trauma, burns, pancreatitis, and autoimmune conditions.
- It is not the current definition of sepsis and does not measure organ dysfunction.
- The criteria perform differently in older adults, pregnancy, and immunocompromised patients.
- A negative SIRS result does not exclude serious infection or sepsis.
Common mistakes
- Counting a temperature of exactly 38 C as positive when the threshold is above 38 C.
- Counting a heart rate of exactly 90 as positive when the threshold is above 90.
- Counting a respiratory rate of exactly 20 as positive when the threshold is above 20.
- Adding respiratory rate and PaCO2 as separate criteria instead of one respiratory criterion.
- Equating SIRS with sepsis without assessing infection and organ dysfunction.
Try it yourself
Quick checks. Answers sit tucked under each question.
Temperature 37.0 C, heart rate 80, respiratory rate 16, PaCO2 40, WBC 8, bands 2 percent. How many criteria?
0 criteria. All values are within the normal range, so SIRS is negative.
Temperature 38.5 C, heart rate 100, respiratory rate 24, WBC 8, bands 2 percent. How many criteria?
3 criteria. Temperature, heart rate, and respiratory rate are positive, so SIRS is positive.
Temperature 38.0 C, heart rate 90, respiratory rate 20, PaCO2 32, WBC 12, bands 10 percent. How many criteria?
0 criteria. Every value sits exactly at a boundary, and the SIRS thresholds are strict, so none count.
Questions
What is SIRS?
Systemic inflammatory response syndrome. It is a set of four bedside criteria that indicate a widespread inflammatory response.
Does SIRS mean sepsis?
No. Sepsis requires infection plus organ dysfunction. SIRS can occur without infection and is no longer part of the Sepsis-3 definition.
How many criteria are needed?
At least two of the four criteria. The criteria are temperature, heart rate, respiratory status, and white blood cell count or bands.
Are the thresholds inclusive?
No. The thresholds are strict. For example, a heart rate of 90 does not count, but 91 does.
Why is mechanical ventilation a respiratory criterion?
Mechanical ventilation indicates respiratory failure and satisfies the respiratory limb of SIRS even when the rate or PaCO2 would not.
Can SIRS be used to decide on antibiotics?
No. Antibiotic decisions depend on the suspected infection, severity, cultures, and local guidance. SIRS alone is too nonspecific.
Sources
- SIRS criteria and sepsis definitions review
- Bone et al., original SIRS consensus
- ACCP/SCCM consensus conference DOI