qSOFA vs SIRS criteria in sepsis: what changed

What SIRS and qSOFA each measure

The SIRS criteria and qSOFA measure different things: SIRS describes an inflammatory response, while qSOFA flags a patient at risk of a poor outcome. The systemic inflammatory response syndrome was defined at a 1991 American consensus conference (Bone and colleagues, Chest, 1992). Two or more of four criteria count: a temperature over 38 °C or under 36 °C, a heart rate over 90, a respiratory rate over 20 or PaCO2 under 32 mmHg, and a white cell count over 12,000/mm³, under 4,000/mm³ or with more than 10% immature bands. Under the old definitions, infection plus SIRS meant sepsis. qSOFA, from Seymour and colleagues in 2016, gives one point each for a respiratory rate of 22 or more, altered mentation and a systolic pressure of 100 mmHg or less, and needs no blood test. A score of 2 or more flags a higher risk of death or a long ICU stay.

Why Sepsis-3 dropped SIRS

The Sepsis-3 task force, reporting in JAMA in 2016 (Singer and colleagues), unanimously considered the use of two or more SIRS criteria to identify sepsis unhelpful. It gave two reasons. First, SIRS criteria are present in many hospitalized patients, including those who never develop infection or come to harm, so they discriminate poorly. Second, they miss patients who are seriously ill. Kaukonen and colleagues studied 109,663 patients with infection and organ failure in 172 intensive care units in Australia and New Zealand (2015). Of these, 12.1%, about 1 in 8, had fewer than two SIRS criteria, yet their characteristics and trends in mortality were similar to the SIRS-positive group. Mortality rose steadily with each additional criterion, with no step at the threshold of two. Sepsis-3 therefore redefined sepsis as life-threatening organ dysfunction caused by a dysregulated host response to infection, measured with the SOFA score, and offered qSOFA as a quick screen for that risk.

Which predicts outcome better?

Outside the ICU, qSOFA predicted death better than SIRS in most large studies, while inside the ICU neither did well. In Seymour's validation of 66,522 encounters with suspected infection outside the ICU, the area under the ROC curve for death in hospital was 0.81 for qSOFA and 0.76 for SIRS. In a prospective study of 879 emergency patients in 30 departments in France, Spain, Belgium and Switzerland (Freund and colleagues, 2017), it was 0.80 for qSOFA against 0.65 for SIRS. Among 184,875 patients admitted to Australian and New Zealand intensive care units with infection (Raith and colleagues, 2017), both were poor, at 0.607 for qSOFA and 0.589 for SIRS, against 0.753 for a SOFA rise of 2 or more. Churpek and colleagues, in 30,677 infected patients on wards and in the emergency department, found 0.69 for qSOFA and 0.65 for SIRS, both below the general early warning scores NEWS (0.77) and MEWS (0.73).

Sensitivity, timing and when to use each

The two tools sit at opposite ends of the trade-off between catching every case and avoiding false alarms. In Churpek's study, two or more SIRS criteria had a sensitivity of 91% but a specificity of only 13% for death or ICU transfer, while a qSOFA of 2 or more had a sensitivity of 54% and a specificity of 67%. Most patients met two SIRS criteria 17 hours before the outcome, against 5 hours for two qSOFA criteria. The authors concluded that qSOFA should not replace general early warning scores in patients with suspected infection. The Surviving Sepsis Campaign 2021 guideline agrees, recommending against using qSOFA, compared with SIRS, NEWS or MEWS, as a single screening tool for sepsis or septic shock. Sepsis-3 notes that SIRS may still help identify infection. In practice, SIRS findings support the suspicion of infection, qSOFA flags who among those patients is at high risk, and neither is a definition of sepsis on its own.

Worked example: two patients the tools split on

Two patients show how SIRS and qSOFA can point in opposite directions. A 30-year-old man with influenza-like illness has a temperature of 38.7 °C, a heart rate of 110, a respiratory rate of 20, a systolic pressure of 120 mmHg, normal mentation and a white cell count of 9,000/mm³. He meets two SIRS criteria, temperature and heart rate, so he would have counted as SIRS positive. His qSOFA is 0, because his respiratory rate, blood pressure and mentation are all normal. An 82-year-old woman with pneumonia has a temperature of 36.8 °C, a heart rate of 88, a respiratory rate of 24, a systolic pressure of 96 mmHg, new confusion and a white cell count of 10,500/mm³. She meets only one SIRS criterion, the respiratory rate, so she is SIRS negative. Her qSOFA is 3, the maximum, which prompts a search for organ dysfunction. Her case is the kind Kaukonen found SIRS can miss.

Enter both patients in the qSOFA calculator to see each result and what Sepsis-3 says it means.