SIRS Criteria vs qSOFA: Sepsis Signs, Sepsis-3 and What EMS Can Measure

Sepsis is the body's response to an infection going wrong and damaging its own organs. It is common, it kills, and it is time-sensitive, and the first person to suspect it is often a field provider. Two sets of criteria dominate how sepsis is talked about: the SIRS criteria from the early 1990s and qSOFA, introduced with the Sepsis-3 definitions in 2016. They answer different questions, and neither was built for the back of an ambulance.

The SIRS criteria

SIRS stands for systemic inflammatory response syndrome. The criteria come from a 1991 consensus conference of the ACCP and the SCCM, published in 1992 by Bone and colleagues. A patient meets SIRS with 2 or more of the four criteria below.

Under those 1992 definitions, now often called Sepsis-1, sepsis was SIRS with a suspected or confirmed infection. Severe sepsis added organ dysfunction, and septic shock added low blood pressure that did not respond to fluid. That ladder is still found in older textbooks and in some protocols.

The weakness of SIRS is that it describes inflammation, not infection or organ damage. A patient who has just run up a flight of stairs, or who is anxious or in pain, can meet it. So can patients with pancreatitis, burns or trauma. And some patients with an infection that is already damaging their organs do not meet it. It catches many patients, which makes it more sensitive than qSOFA, but it is not specific to sepsis.

Sepsis-3 and qSOFA

In 2016 the Sepsis-3 definitions, published by Singer and colleagues, redefined sepsis as life-threatening organ dysfunction caused by a dysregulated host response to infection. In hospital, organ dysfunction is measured as a rise of 2 points or more in the SOFA score, which needs laboratory tests. The term severe sepsis was retired, because sepsis now means organ dysfunction by definition. Septic shock became a subset of sepsis with circulatory and cellular problems severe enough to substantially raise the risk of death, defined in hospital terms by the need for vasopressors and a raised lactate despite adequate fluid resuscitation.

Sepsis-3 also introduced qSOFA (quick SOFA), a bedside score needing no laboratory test, derived by Seymour and colleagues. It scores one point each for a respiratory rate of 22 or more, altered mentation and a systolic pressure of 100 mmHg or less. A score of 2 or more flags an adult with suspected infection who is at higher risk of a poor outcome.

• qSOFA is a prognostic score, not a diagnosis of sepsis.
• A score below 2 does not rule sepsis out.
• It was derived in adults and is not validated in children.
• The Surviving Sepsis Campaign's 2021 guideline recommends against using qSOFA, compared with SIRS, NEWS or MEWS, as a single screening tool for sepsis or septic shock. It is more specific than SIRS but misses too many patients to be relied on alone.

Score qSOFA for an adult with suspected infection

SIRS vs qSOFA

What EMS can measure in the field

Neither set of criteria fits the field perfectly. EMS has no white count and no arterial blood gas, so a field SIRS count is out of three, not four. qSOFA's three items are all measurable in the field, but its low sensitivity is the reason it is not recommended as a screen on its own.

EtCO2 as a perfusion clue

Capnography is not part of SIRS or qSOFA, but it can help. In sepsis, a low EtCO2 can reflect two things at once: the patient breathing fast to blow off acid as lactate builds up, and less carbon dioxide reaching the lungs as perfusion falls. Prehospital studies have associated a low EtCO2 in suspected sepsis with a raised lactate and a worse outcome, and some EMS sepsis screens include it. A low reading has other causes, including simple hyperventilation and very shallow breathing, so read it with the waveform and the patient. Your protocol says whether and how your service uses it.

Prehospital sepsis screening tools

Because neither SIRS nor qSOFA was designed for EMS, many services use a prehospital sepsis screen of their own or a published one. Some combine a suspected infection with field-measurable signs from SIRS, some add EtCO2 or a point-of-care lactate, and some use a general early warning score such as NEWS2. They differ in their criteria and their thresholds, and none is the national standard. The screen in your protocol is the one your service uses, and a positive screen usually triggers early notification of the receiving facility.

Sepsis signs to look for

• A suspected source of infection: a cough, urinary symptoms, a wound or skin infection, abdominal pain, an indwelling catheter or line, or recent surgery.
• Fever or a low temperature, chills or rigors.
• A fast heart rate and fast breathing.
• New confusion, drowsiness or a change from the patient's normal behavior.
• Skin that is warm and flushed early, or cool, pale and mottled later.
• Low blood pressure, which is a late sign.
• Little or no urine output over the past day.
• A patient or family member who says this is the sickest they have ever felt or seen them.

Special populations

• Older adults may have no fever, may be hypothermic, and may show confusion or a fall as the only sign.
• Patients with a weakened immune system, from chemotherapy, transplant drugs, steroids or other causes, can become septic fast with few signs.
• Beta blockers and pacemakers can hide a rising heart rate.
• Children are not small adults: qSOFA is not validated in them, the adult SIRS figures do not apply, and pediatric criteria use age-specific values. A separate pediatric sepsis definition, the Phoenix criteria, was published in 2024. Low blood pressure in a child is a late, ominous sign.

Field priorities

The principles below are common to EMS curricula. How each one is carried out, and every fluid volume, blood pressure target and medication, is set by your protocol and your medical direction.

• Think of sepsis. A patient with a suspected infection and abnormal vital signs should be screened for sepsis, and treated as possible sepsis until your assessment or the hospital says otherwise.
• Airway, breathing and oxygenation: give oxygen to correct a low saturation, titrated as your protocol directs.
• Screen with your protocol's sepsis tool and notify the receiving facility early if it is positive.
• Vascular access and fluids as your protocol directs. Every volume, and any medication, is your protocol's.
• Check a temperature and a blood glucose, and put the patient on the monitor.
• Find out the likely source of infection, when the illness started, and the medication and allergy list, and pass it on at handoff.
• Reassess often and trend the respiratory rate, heart rate, blood pressure, mentation and EtCO2.
• Transport without delay, and let your protocol decide the destination.

Calculate the shock index from a heart rate and a systolic pressure

The short version

• SIRS (1992): temperature above 38 or below 36 °C, heart rate above 90, respiratory rate above 20 or PaCO2 below 32 mmHg, white count above 12,000 or below 4,000 or more than 10% bands. Two or more meets SIRS.
• SIRS is more sensitive than qSOFA but not specific: it describes inflammation, not infection, and some septic patients do not meet it.
• Sepsis-3 (2016) defines sepsis as organ dysfunction from a dysregulated response to infection, and introduced qSOFA.
• qSOFA: respiratory rate 22 or more, altered mentation, systolic 100 or less. Two or more flags higher risk; below 2 does not rule sepsis out, and it is not validated in children.
• The Surviving Sepsis Campaign 2021 recommends against using qSOFA alone as a screening tool.
• In the field there is no white count, so use your protocol's sepsis screen, watch the EtCO2 and the trend, notify early and transport.