Diagnostic Criteria for Sepsis
Sepsis is diagnosed when a patient has documented or suspected infection PLUS evidence of life-threatening organ dysfunction caused by a dysregulated host response to that infection, as defined by the Third International Consensus Definitions (Sepsis-3). 1
Core Diagnostic Framework
The diagnosis requires two essential components that must both be present:
1. Documented or Suspected Infection
- Any confirmed or clinically suspected source of infection (bacterial, fungal, or viral) 1, 2
- Blood cultures, imaging, or clinical findings suggesting an infectious process 1
2. Evidence of Organ Dysfunction from Dysregulated Host Response
This is what separates sepsis from simple infection - the presence of an aberrant host response causing organ dysfunction, not just the infection itself 1
Clinical Criteria Categories
Sepsis can be identified through any combination of the following categories of abnormalities in a patient with suspected infection 1, 2:
General Variables
- Fever (>38.3°C) or hypothermia (<36°C) 1, 2
- Tachycardia (>90 beats/min or >2 SD above normal for age) 1, 2
- Tachypnea (>30 breaths/min) 1, 2
- Altered mental status 1, 2
- Significant edema or positive fluid balance (>20 mL/kg over 24 hours) 1, 2
- Hyperglycemia (>140 mg/dL or 7.7 mmol/L) in absence of diabetes 1, 2
Inflammatory Variables
- Leukocytosis (WBC >12,000/μL) or leukopenia (WBC <4,000/μL) 1, 2
- Normal WBC with >10% immature forms (bandemia) 1, 2
- Elevated C-reactive protein or procalcitonin (>2 SD above normal) 1, 2
Hemodynamic Variables
Organ Dysfunction Variables
- Arterial hypoxemia (PaO₂/FiO₂ <300) 1, 2
- Acute oliguria (urine output <0.5 mL/kg/h for ≥2 hours despite adequate fluid resuscitation) 1, 2
- Creatinine increase ≥0.5 mg/dL or 44.2 μmol/L 1, 2
- Coagulation abnormalities (INR >1.5 or aPTT >60 seconds) 1, 2
- Ileus (absent bowel sounds) 1, 2
- Thrombocytopenia (platelet count <100,000/μL) 1, 2
- Hyperbilirubinemia (total bilirubin >4 mg/dL or 70 μmol/L) 1, 2
Tissue Perfusion Variables
- Hyperlactatemia (>1 mmol/L, with >2 mmol/L indicating septic shock when combined with hypotension requiring vasopressors) 1, 2
- Decreased capillary refill or mottling 1, 2
Practical Clinical Application
You do NOT need all criteria present - systematically assess all categories when evaluating suspected infection, and the presence of findings from multiple categories strengthens the diagnosis 2. For example, a patient with pneumonia presenting with fever, tachycardia, tachypnea, and hypoxemia meets sepsis criteria without requiring altered mental status 2.
Critical Distinction: Severe Sepsis
Severe sepsis is diagnosed when sepsis is accompanied by:
- Sepsis-induced hypotension 1
- Lactate above upper laboratory limits 1
- Urine output <0.5 mL/kg/h for >2 hours despite adequate resuscitation 1
- Acute lung injury (PaO₂/FiO₂ <250 without pneumonia or <200 with pneumonia) 1
- Creatinine >2.0 mg/dL 1
- Bilirubin >2 mg/dL 1
- Platelet count <100,000/μL 1
- Coagulopathy (INR >1.5) 1
Special Populations
Pediatric Patients
In children, sepsis requires signs of inflammation plus infection with hyper- or hypothermia (rectal temperature >38.5°C or <35°C), tachycardia, and at least one of: altered mental status, hypoxemia, increased serum lactate, or bounding pulses 1, 2.
Neutropenic Patients
In neutropenic patients, white blood cell count cannot be used as a criterion - all other criteria apply normally 1.
Common Pitfalls
The 2016 Sepsis-3 definition moved away from SIRS criteria alone because they are overly sensitive and nonspecific - many patients with simple infections meet SIRS criteria without having sepsis 1, 3. The key differentiator is organ dysfunction from a dysregulated host response, not just inflammation 1, 4.
No single laboratory test accurately diagnoses sepsis - the diagnosis requires clinical integration of infection evidence with organ dysfunction markers 5. Biomarkers like procalcitonin and lactate support but do not independently establish the diagnosis 5.