SIRS Criteria

The SIRS (Systemic Inflammatory Response Syndrome) scale or criteria were established to identify a generalized and uncontrolled inflammatory state in the body, which can be triggered by a variety of severe insults, including, but not limited to, infection (which, when present, defines sepsis), as well as trauma, burns, pancreatitis, and major surgeries. SIRS is not a specific disease, but rather a clinical response to a harmful stimulus. The scale is defined by the presence of two or more of the following four clinical and laboratory criteria: (1) Temperature, indicating fever (core temperature > 38°C or 100.4°F) or hypothermia (core temperature < 36°C or 96.8°F); (2) Heart rate, indicating tachycardia (heart rate > 90 beats per minute); (3) Respiratory rate, indicating tachypnea (respiratory rate > 20 breaths per minute or, in mechanically ventilated patients, an arterial partial pressure of carbon dioxide (PaCO2) < 32 mmHg); and (4) White blood cell count (WBC), indicating leukocytosis (WBC > 12,000/mm³), leukopenia (WBC < 4,000/mm³), or the presence of more than 10% immature forms (band cells). The presence of two or more of these criteria confirms SIRS. Although historically fundamental for the definition of sepsis (SIRS + infection), its use has been re-evaluated, as these criteria can be non-specific (present in many non-severe conditions) or absent in some septic patients. The Sepsis-3 consensus (2016) began to prioritize the SOFA and qSOFA scores for identifying sepsis, which is now defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, moving away from the SIRS-based definition.