What are the current criteria for diagnosing sepsis, including qSOFA and SOFA definitions?

Current Sepsis Diagnostic Criteria

Use the Sepsis-3 definition: sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, operationalized as an increase in SOFA score of ≥2 points in patients with suspected or confirmed infection. 1, 2

Core Diagnostic Framework

Sepsis Definition (Sepsis-3)

The current standard requires two components:

1. Suspected or confirmed infection
2. Organ dysfunction: Increase in Sequential Organ Failure Assessment (SOFA) score ≥2 points from baseline 1, 3

This SOFA threshold is associated with in-hospital mortality >10% and represents the critical distinction between simple infection and sepsis 3.

SOFA Score Components

The SOFA score assesses six organ systems (0-4 points each, maximum 24 points):

• Respiratory: PaO2/FiO2 ratio
• Coagulation: Platelet count
• Hepatic: Bilirubin level
• Cardiovascular: Mean arterial pressure or vasopressor requirement
• Neurologic: Glasgow Coma Scale
• Renal: Creatinine or urine output 3

Important caveat: The term "severe sepsis" is now obsolete and should not be used 1.

Quick SOFA (qSOFA) for Rapid Screening

When to Use qSOFA

Apply qSOFA outside the ICU (emergency departments, general wards, out-of-hospital settings) to rapidly identify patients with suspected infection at risk for poor outcomes 1, 3.

qSOFA Criteria (≥2 points indicates high risk)

• Respiratory rate ≥22/min (1 point)
• Altered mentation (1 point)
• Systolic blood pressure ≤100 mmHg (1 point) 1, 4, 3

Performance Characteristics

Critical limitation: qSOFA has low sensitivity (42%) but high specificity (98%) for sepsis diagnosis 5. This means:

• qSOFA ≥2 strongly suggests sepsis risk (high specificity)
• qSOFA <2 does NOT rule out sepsis (low sensitivity)

Therefore, do not rely on qSOFA alone for sepsis screening 5, 6. The 2021 Surviving Sepsis Campaign Guidelines explicitly discourage using qSOFA as the sole screening tool 6.

Enhanced Screening Approaches

To improve sensitivity while maintaining specificity, combine qSOFA with additional markers:

• qSOFA + lactate: Sensitivity 87.5%, specificity 81.4% 6
• qSOFA + capillary refill time: Sensitivity 83.3%, specificity 81.4% 6

Alternatively, use NEWS (National Early Warning Score) for screening, which demonstrates superior diagnostic capability with sensitivity 71% and specificity 85% for sepsis prediction 5.

Septic Shock Definition

Septic shock is a subset of sepsis requiring BOTH:

1. Vasopressor requirement to maintain mean arterial pressure ≥65 mmHg
2. Serum lactate >2 mmol/L (>18 mg/dL) in the absence of hypovolemia 1, 3

This combination is associated with hospital mortality >40% 3.

Alternative Definitions Still in Use

Sepsis-2 Criteria (Older Definition)

Some guidelines still reference Sepsis-2, which requires:

• Proven or suspected infection PLUS
• ≥2 SIRS criteria:
  • Heart rate >90 bpm
  • Respiratory rate ≥20/min or PaCO2 <32 mmHg
  • Temperature <36°C or >38°C
  • WBC <4×10⁶ or >12×10⁶/L or >10% immature forms 4

However, SIRS has poor predictive validity (AUROC 0.64 for ICU mortality, sensitivity 85% but specificity only 41%) and should not be the primary diagnostic criterion 5, 7.

Practical Clinical Algorithm

Step 1: Identify Suspected Infection

Look for clinical evidence or high suspicion of infection based on:

• Altered mental status
• Hypotension (systolic BP <90-100 mmHg)
• Tachypnea (respiratory rate >22-24/min)
• Mottled skin/delayed capillary refill
• Elevated lactate
• Temperature abnormalities 4

Step 2: Assess for Organ Dysfunction

In ICU settings: Calculate full SOFA score. An increase ≥2 points confirms sepsis 3, 7.

Outside ICU: Calculate qSOFA score. If ≥2 points, strongly suspect sepsis and proceed with full SOFA assessment 3, 7.

Step 3: Measure Lactate

All patients with suspected sepsis should have lactate measured to:

• Enhance diagnostic accuracy when combined with qSOFA 6
• Identify septic shock (lactate >2 mmol/L with vasopressor requirement) 1
• Guide resuscitation efforts 4

Step 4: Risk Stratification

• qSOFA ≥2 or SOFA increase ≥2: High risk, initiate sepsis protocols immediately
• qSOFA <2 but clinical concern: Do not exclude sepsis; calculate full SOFA score and measure lactate
• NEWS ≥7: High risk of severe illness or death from sepsis 8

Common Pitfalls to Avoid

1. Do not use qSOFA alone for sepsis screening due to low sensitivity 5, 6
2. Do not use SIRS criteria as the primary diagnostic tool—they lack specificity and are no longer recommended 5, 3, 7
3. Do not assume normal vital signs exclude sepsis—elderly and immunocompromised patients may have attenuated responses 1
4. Do not delay treatment while calculating scores—clinical judgment supersedes scoring systems 8
5. Do not forget baseline organ function—SOFA requires comparison to baseline, assume baseline of zero if unknown 3