MAGENT

SIRS criteria: the four items and how they're counted

The systemic inflammatory response syndrome (SIRS) criteria are four items from a 1992 consensus definition: temperature, heart rate, breathing, and white blood cell count. Each item counts as 1 when its measurement is outside the published limits, so the count runs from 0 to 4. A patient with a heart rate of 91 beats per minute and a respiratory rate of 21 breaths per minute, with temperature and white cell count inside the limits, meets 2 of the 4 criteria.

Not a medical device. Not a diagnosis or dosing recommendation.

Use this calculator via API

What are the SIRS criteria?

SIRS is a term defined at a 1991 American College of Chest Physicians and Society of Critical Care Medicine (ACCP/SCCM) consensus conference and published in 1992 by Bone and colleagues. The criteria describe a body-wide inflammatory response using four everyday measurements.

They're sometimes called the SIRS score, the Bone 1992 criteria or the ACCP/SCCM SIRS criteria. They aren't the Sepsis-3 definitions, qSOFA or SOFA.

This page explains how each item is counted and how the count is added up. The count behind the calculator's yes/no SIRS result appears only in the exact expression the calculator uses, below; this page doesn't say what a count means for a patient.

The SIRS criteria formula

criteria met = temperature item + heart rate item + respiratory item + white cell item
  temperature item  = 1 if temperature > 38 °C or < 36 °C
  heart rate item   = 1 if heart rate > 90 beats/min
  respiratory item  = 1 if respiratory rate > 20 breaths/min or PaCO2 < 32 mm Hg
  white cell item   = 1 if WBC > 12,000/µL or < 4,000/µL or bands > 10%
(each item 0 or 1; total 0 to 4)

Exact expression the calculator uses:

SIRS present iff >=2 of 4: (temperature_c >38 or <36) + (heart_rate_bpm >90) + (respiratory_rate >20 or paco2_mm_hg <32) + (wbc_per_ul >12000 or <4000 or band_percent >10); each 1; max 4

In words: check each of the four items, give it 1 if it's met and 0 if not, and add the four numbers.

What each part means

InputPlain-English meaningUnitAccepted range
temperature_cBody temperature°C30.0–45.0
heart_rate_bpmHeart ratebeats/minwhole number, 30–220
respiratory_rateBreaths per minutebreaths/minwhole number, 4–80
paco2_mm_hgArterial carbon dioxide pressure (optional)mm Hg8–80
wbc_ul or wbc_k_ulWhite blood cell countcells/µL, or 10³/µL10–500,000, or 0.01–500
band_percentImmature (band) neutrophils as a share of white cells (optional)%0–100
sirs_criteria_metNumber of items metcount0–4

How the count works

  1. Temperature. Counts if it's above 38 °C or below 36 °C.
  2. Heart rate. Counts if it's above 90 beats per minute.
  3. Breathing. Counts if the respiratory rate is above 20 breaths per minute, or if a PaCO2 is given and it's below 32 mm Hg. Either one is enough; the item still counts as 1, not 2.
  4. White cells. Counts if the count is above 12,000/µL or below 4,000/µL, or if a band percentage is given and it's above 10%. Again, it's 1 point at most.
  5. Add the four items for a total from 0 to 4.

Every limit is a strict inequality. A temperature of exactly 38.0 °C, a heart rate of exactly 90 or a white count of exactly 12,000 doesn't count.

Units

  • White cells in cells/µL or 10³/µL. 8,000 cells/µL is the same as 8.0 × 10³/µL (and 8.0 × 10⁹/L). The calculator accepts either form and converts to cells/µL.
  • Temperature in °C. Convert Fahrenheit first.
  • PaCO2 and bands are optional. If they're left out, the breathing item uses the respiratory rate alone and the white-cell item uses the count alone.

The calculator also returns a yes/no SIRS result derived from the count; the exact expression above shows the rule it uses.

Worked examples

These use Magent's own expected values for the calculator.

Example 1: temperature 37.0 °C, heart rate 80, respiratory rate 16, WBC 8,000/µL

  1. Temperature: 37.0 is between 36 and 38 → 0
  2. Heart rate: 80 is not above 90 → 0
  3. Breathing: 16 is not above 20 → 0
  4. White cells: 8,000 is between 4,000 and 12,000 → 0
  5. Criteria met: 0 of 4

Example 2: same, but heart rate 91 and respiratory rate 21

  1. Heart rate 91 is above 90 → 1
  2. Respiratory rate 21 is above 20 → 1
  3. Temperature and white cells → 0
  4. Criteria met: 2 of 4

Example 3: temperature exactly 38.0 °C, everything else as Example 1

  1. 38.0 is not above 38 → 0
  2. Criteria met: 0 of 4

Raise the temperature to 38.1 °C and the temperature item counts: 1 of 4.

Example 4: PaCO2 31 mm Hg with a respiratory rate of 16

  1. Respiratory rate 16 doesn't count on its own.
  2. PaCO2 31 is below 32 → the breathing item counts.
  3. Criteria met: 1 of 4

Example 5: white count entered as 8.0 × 10³/µL

  1. 8.0 × 1,000 = 8,000 cells/µL
  2. Same as Example 1 → 0 of 4

SIRS criteria edge values

These come from Magent's expected values for the calculator. Each changes a single measurement from Example 1 and shows exactly where each item starts to count. A temperature of 38.0 °C or 36.0 °C doesn't count (0 criteria met), while 38.1 °C or 35.9 °C does (1). A heart rate of 90 doesn't count and 91 does. A respiratory rate of 20 doesn't count and 21 does. A PaCO2 of 32 mm Hg doesn't count and 31 mm Hg does. A white count of 12,000/µL or 4,000/µL doesn't count, while 12,001/µL or 3,999/µL does. Bands of 10% don't count and 10.1% do.

History of the SIRS criteria

The criteria come from Roger C. Bone, Robert A. Balk, Frank B. Cerra and colleagues, Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis, published in Chest in 1992 (volume 101, issue 6, pages 1644–1655).

The abstract describes a consensus conference held in Northbrook with the goal of agreeing definitions for patients with sepsis and its sequelae. It says broad definitions of sepsis and of the systemic inflammatory response syndrome were proposed, along with detailed physiologic parameters by which a patient may be categorized.

When it's used

A 2017 cohort study in the Revista Brasileira de Terapia Intensiva notes that since 1992 more than 100 clinical trials have used the SIRS criteria to select patients.[1] It also describes debate over how well the criteria pick out the sickest patients.[1]

Where it's used

The same study cites work finding that up to 64% of ward patients develop SIRS during their hospital stay, and another estimate of nearly 50%.[1] It points out that SIRS can occur with common conditions that aren't infections, such as high-risk surgery.[1]

Who uses it

The criteria are used in research to define study groups, and the 2017 paper mentions authors who have argued for documenting SIRS status routinely on hospital admission.[1] It notes that the Sepsis-3 task force suggested SIRS is still useful for identifying infection.[1]

Limits of the calculation

  • It counts four items. It doesn't diagnose sepsis, severe sepsis or septic shock.
  • The 2017 study describes the criteria's low specificity and cites a study in which they missed one in eight patients with severe sepsis.[1]
  • It's the 1992 ACCP/SCCM definition. It isn't Sepsis-3, qSOFA or SOFA.
  • The calculator doesn't ask whether infection is suspected.
  • PaCO2 and band percentage are optional; leaving them out can lower the count.
  • Inputs outside the accepted ranges are rejected, not estimated.

Clinical decisions belong to a qualified clinician who knows the patient.

  • qSOFA is the Sepsis-3 score from respiratory rate, altered mentation and systolic blood pressure, out of 3. It doesn't use temperature or white cells.
  • SOFA is a separate score. SIRS counts four yes/no items.

Glossary

  • SIRS: systemic inflammatory response syndrome, the body-wide response the 1992 criteria describe.
  • PaCO2: the pressure of carbon dioxide in arterial blood, measured from a blood gas.
  • Bands: immature neutrophils, reported as a percentage of white cells.
  • WBC: white blood cell count.

Common mistakes

  • Counting a limit value. 38.0 °C, 90 beats/min, 20 breaths/min and 12,000/µL don't count.
  • Scoring breathing twice. A high respiratory rate and a low PaCO2 together still make 1 point.
  • Entering white cells in the wrong unit. 8,000/µL is 8.0 in 10³/µL, not 8,000.
  • Treating SIRS as Sepsis-3. They're different definitions with different inputs.

Source

Bone RC, Balk RA, Cerra FB, et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Chest. 1992;101(6):1644-1655. DOI: 10.1378/chest.101.6.1644

Further reading

  1. Taniguchi LU, Pires EMC, Vieira JM Jr, Azevedo LCP. Systemic inflammatory response syndrome criteria and the prediction of hospital mortality in critically ill patients: a retrospective cohort study. Rev Bras Ter Intensiva. 2017;29(3):317-324.

Frequently asked questions

What are the four SIRS criteria?

Temperature above 38 °C or below 36 °C; heart rate above 90; respiratory rate above 20 or PaCO2 below 32 mm Hg; and white count above 12,000/µL or below 4,000/µL or bands above 10%.

How many SIRS criteria are needed for SIRS?

The exact expression above shows the count the calculator uses for its yes/no field. This page doesn't say what a count means for a patient; that depends on the clinical context.

Does a temperature of exactly 38 °C count?

No. The limit is strictly above 38 °C, so 38.0 doesn't count and 38.1 does.

Is SIRS the same as sepsis?

No. SIRS describes an inflammatory response, and the 2017 study notes it can occur without infection, for example after high-risk surgery.[1]

What's the difference between SIRS and qSOFA?

qSOFA is a Sepsis-3 score from respiratory rate, mentation and systolic blood pressure. SIRS uses temperature, heart rate, breathing and white cells.

Who defined the SIRS criteria?

An ACCP/SCCM consensus conference in 1991, published by Roger Bone and colleagues in Chest in 1992.