What are the diagnostic criteria for sepsis?

Diagnostic Criteria for Sepsis

Sepsis is diagnosed when there is documented or suspected infection accompanied by evidence of organ dysfunction, assessed using clinical criteria that include general variables (fever/hypothermia, tachycardia, tachypnea, altered mental status), inflammatory markers (leukocytosis/leukopenia, elevated CRP or procalcitonin), hemodynamic changes (hypotension), organ dysfunction parameters (hypoxemia, oliguria, elevated creatinine, coagulopathy, thrombocytopenia, hyperbilirubinemia), and tissue perfusion abnormalities (hyperlactatemia, decreased capillary refill). 1, 2

Core Diagnostic Requirements

The diagnosis of sepsis requires two fundamental components:

• Documented or suspected infection as the prerequisite 1, 3, 2
• Evidence of organ dysfunction or dysregulated host response manifested through multiple clinical and laboratory parameters 3, 2

Specific Diagnostic Parameters

General Variables

• Fever: Core temperature >38.3°C 1, 2
• Hypothermia: Core temperature <36°C 1, 2
• Tachycardia: Heart rate >90 beats/min or >2 standard deviations above normal for age 1, 2
• Tachypnea: Respiratory rate >20 breaths/min 2
• Altered mental status 1, 2
• Significant edema or positive fluid balance: >20 mL/kg over 24 hours 1, 2
• Hyperglycemia: Plasma glucose >140 mg/dL (or >7.7 mmol/L) in absence of diabetes 1, 2

Inflammatory Variables

• Leukocytosis: WBC count >12,000/μL 1, 2
• Leukopenia: WBC count <4,000/μL 1, 2
• Normal WBC with >10% immature forms (left shift) 1, 2
• Elevated C-reactive protein: >2 standard deviations above normal 1, 2
• Elevated procalcitonin: >2 standard deviations above normal 1, 2

Hemodynamic Variables

• Arterial hypotension: Systolic BP <90 mmHg, MAP <70 mmHg, or SBP decrease >40 mmHg in adults 1, 2
• Mixed venous oxygen saturation >70% 2
• Cardiac index >3.5 L/min/m² 2

Organ Dysfunction Variables

• Arterial hypoxemia: PaO₂/FiO₂ <300 1, 2
• Acute oliguria: Urine output <0.5 mL/kg/h for at least 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: Plasma total bilirubin >4 mg/dL (or >70 μmol/L) 1, 2

Tissue Perfusion Variables

• Hyperlactatemia: >1 mmol/L 1, 2
• Decreased capillary refill or mottling 1, 2

Severe Sepsis Criteria

Severe sepsis is defined as sepsis with evidence of organ dysfunction or tissue hypoperfusion, documented by one or more of the following 1, 2:

• Sepsis-induced hypotension 1, 2
• Lactate above upper normal limits 1, 2
• Urine output <0.5 mL/kg/h for >2 hours despite adequate fluid resuscitation 1, 2
• Acute lung injury: PaO₂/FiO₂ <250 (without pneumonia) or <200 (with pneumonia as source) 1, 2
• Creatinine >2.0 mg/dL (176.8 μmol/L) 1, 2
• Bilirubin >2 mg/dL (34.2 μmol/L) 1, 2
• Platelet count <100,000/μL 1, 2
• Coagulopathy: INR >1.5 1, 2

Modern Assessment Tools

SOFA Score

The Sequential Organ Failure Assessment (SOFA) score is the primary tool for diagnosing sepsis-related organ dysfunction, assessing respiratory, cardiovascular, hepatic, coagulation, renal, and neurological function 3. This represents the contemporary approach to sepsis diagnosis, defining sepsis as "life-threatening organ dysfunction caused by a dysregulated host response to infection" 3.

NEWS2 Score

The National Early Warning Score 2 (NEWS2) is recommended for initial evaluation of sepsis risk 3:

• Score 0: Very low risk 3
• Score 1-4: Low risk 3
• Score 5-6: Moderate risk 3
• Score ≥7: High risk 3
• Score of 3 in any single parameter: May indicate increased sepsis risk 3

Special Population Considerations

Neutropenic Patients

In neutropenic patients, white blood cell count cannot be used as a criterion to define sepsis 1, 2. All other diagnostic criteria remain applicable, with the same definitions for severe sepsis and septic shock 1.

Pediatric Population

Pediatric sepsis criteria include signs of inflammation plus infection with hyper- or hypothermia (rectal temperature >38.5°C or <35°C), tachycardia (may be absent in hypothermic patients), and at least one indication of altered organ function: altered mental status, hypoxemia, increased serum lactate, or bounding pulses 1.

Important Clinical Caveats

The presence of infection plus any combination of the above parameters supports the diagnosis of sepsis—there is no requirement for a specific number of criteria to be met, though the traditional SIRS criteria (requiring ≥2 criteria) have been shown to miss 12.1% of patients with infection, organ failure, and substantial mortality 4. The risk of death increases linearly with each additional criterion rather than at a specific threshold 4.

Early recognition is critical as time to adequate treatment directly impacts outcomes 5. Systemic symptoms including altered mental status, dyspnea, gastrointestinal symptoms, and muscle weakness should be considered warning signs when combined with other infection indicators 5.