What are the criteria to diagnose sepsis?

Diagnostic Criteria for Sepsis

Sepsis is diagnosed when there is documented or suspected infection plus life-threatening organ dysfunction, operationalized as an increase in the Sequential Organ Failure Assessment (SOFA) score of 2 or more points, which is associated with in-hospital mortality greater than 10%. 1

Core Diagnostic Framework

The most current definition (Sepsis-3) requires two essential components 1:

• Documented or suspected infection (clinical evidence or microbiological confirmation)
• Organ dysfunction defined as SOFA score increase ≥2 points from baseline

This represents a fundamental shift from older criteria that emphasized systemic inflammation (SIRS criteria), which have been shown to lack specificity and are no longer recommended as the primary diagnostic framework 1.

Sequential Organ Failure Assessment (SOFA) Score

The SOFA score is the gold standard for identifying sepsis-related organ dysfunction and assesses six organ systems 2, 3:

• Respiratory: PaO2/FiO2 ratio <300 or SpO2 ≤90% 2
• Cardiovascular: Hypotension (SBP <90 mmHg or MAP <70 mmHg) or vasopressor requirement 4, 2
• Renal: Creatinine >2.0 mg/dL (176.8 μmol/L) or urine output <0.5 mL/kg/h for ≥2 hours 4, 2
• Hepatic: Bilirubin >2 mg/dL (34.2 μmol/L) 4, 2
• Coagulation: Platelets <100,000/μL or INR >1.5 4, 2
• Neurological: Altered mental status or decreased Glasgow Coma Scale 2

SOFA demonstrates superior discrimination for mortality (AUROC 0.753) compared to SIRS criteria (AUROC 0.589) or qSOFA (AUROC 0.607) in critically ill patients with suspected infection 3.

Bedside Screening: Quick SOFA (qSOFA)

For initial screening outside the ICU (emergency department, general wards), qSOFA can rapidly identify high-risk patients 1:

qSOFA criteria (≥2 of 3 indicates higher risk):

• Respiratory rate ≥22/min
• Altered mental status
• Systolic blood pressure ≤100 mmHg

Critical caveat: qSOFA has high specificity (96.1%) but poor sensitivity (29.7%) for organ dysfunction, meaning it misses many sepsis cases 5. It should be used only as a screening tool to prompt further evaluation, not as a diagnostic criterion 1, 6. Only one in six qSOFA-positive patients actually has sepsis 6.

Alternative Diagnostic Criteria (Sepsis-2, Still Clinically Relevant)

The 2012 Surviving Sepsis Campaign criteria remain useful for comprehensive assessment and require documented or suspected infection plus any of the following 4, 7:

General Variables

• Fever >38.3°C or hypothermia <36°C 4, 7
• Heart rate >90/min or >2 SD above normal for age 4, 7
• Tachypnea 4, 7
• Altered mental status 4, 7
• Significant edema or positive fluid balance (>20 mL/kg over 24h) 4, 7
• Hyperglycemia (>140 mg/dL or 7.7 mmol/L) without diabetes 4, 7

Inflammatory Variables

• Leukocytosis (WBC >12,000/μL) or leukopenia (WBC <4,000/μL) 4, 7
• Normal WBC with >10% immature forms (bandemia) 4, 7
• Elevated C-reactive protein or procalcitonin (>2 SD above normal) 4, 7

Hemodynamic Variables

• Arterial hypotension (SBP <90 mmHg, MAP <70 mmHg, or SBP decrease >40 mmHg) 4, 7

Organ Dysfunction Variables

• Arterial hypoxemia (PaO2/FiO2 <300) 4, 7
• Acute oliguria (urine output <0.5 mL/kg/h for ≥2h despite adequate fluid resuscitation) 4, 7
• Creatinine increase >0.5 mg/dL or 44.2 μmol/L 4, 7
• Coagulation abnormalities (INR >1.5 or prolonged aPTT) 4, 7
• Ileus (absent bowel sounds) 4, 7
• Thrombocytopenia (platelets <100,000/μL) 4, 7
• Hyperbilirubinemia (total bilirubin >4 mg/dL or 70 μmol/L) 4, 7

Tissue Perfusion Variables

• Hyperlactatemia (>1 mmol/L) 4, 7
• Decreased capillary refill or mottling 4, 7

Important note: SIRS criteria (fever, tachycardia, tachypnea, leukocytosis) were associated with increased risk of organ dysfunction (RR 3.5) and mortality (OR 3.2) in prospective studies, suggesting their abandonment may be premature 5. The Sepsis-2 criteria provide more granular prognostic information about specific organ dysfunctions 5.

Septic Shock Criteria

Septic shock is diagnosed when sepsis is present plus 1:

• Vasopressor requirement to maintain MAP ≥65 mmHg AND
• Serum lactate >2 mmol/L (>18 mg/dL) in the absence of hypovolemia

This combination is associated with hospital mortality >40% 1.

Pediatric Considerations

In children, sepsis requires signs of inflammation plus infection with 4:

• Hyper- or hypothermia (rectal temperature >38.5°C or <35°C)
• Tachycardia (may be absent in hypothermia)
• At least one of: altered mental status, hypoxemia, increased lactate, or bounding pulses 4, 7

Risk Stratification and Re-evaluation

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

• Score 0: Very low risk
• Score 1-4: Low risk (re-evaluate every 4-6 hours)
• Score 5-6: Moderate risk (re-evaluate every hour)
• Score ≥7: High risk (re-evaluate every 30 minutes)
• Score ≥3 in any single parameter: Increased sepsis risk 2

Practical Clinical Algorithm

1. Identify suspected infection (clinical signs, imaging, cultures) 1
2. Calculate SOFA score (or estimate baseline and current scores) 1
3. If SOFA increase ≥2 points: Diagnose sepsis 1
4. Assess for septic shock: Check for vasopressor need + lactate >2 mmol/L 1
5. If outside ICU and SOFA unavailable: Use qSOFA for screening, but recognize its limitations 1, 5
6. Consider comprehensive Sepsis-2 criteria for additional prognostic information about specific organ dysfunctions 5

Common Pitfalls

• Do not rely solely on qSOFA for diagnosis—it misses 70% of sepsis cases due to poor sensitivity 5, 6
• Do not dismiss SIRS criteria entirely—they retain prognostic value despite being removed from Sepsis-3 definitions 5
• Do not diagnose sepsis without evidence of organ dysfunction—infection alone is not sepsis 1
• Do not overlook baseline organ function—SOFA requires comparison to baseline, assume zero if unknown 1