Sepsis Diagnosis and Risk Stratification

Core Diagnostic Framework

The National Health Service recommends using the NEWS2 scoring system combined with suspected or confirmed infection as the primary clinical tool to diagnose and risk-stratify sepsis in patients aged 16 and over 1
The Society of Critical Care Medicine suggests that the diagnosis of sepsis requires two essential components: evidence of infection AND evidence of organ dysfunction or systemic inflammatory response 2

The NEWS2 score incorporates six physiological parameters, each scored to create an aggregate that determines sepsis risk: respiratory rate, oxygen saturation, supplemental oxygen requirement, systolic blood pressure, heart rate, and level of consciousness 1, 3, 4
A score ≥7 indicates high risk of severe illness or death from sepsis, 5-6 indicates moderate risk, 1-4 indicates low risk, and 0 indicates very low risk 1, 3

The Intensive Care Medicine society states that immediately evaluating for high sepsis risk is necessary if any of the following are present, regardless of NEWS2 score: mottled or ashen skin appearance, non-blanching petechial or purpuric rash, or cyanosis of skin, lips, or tongue 5

The Society of Critical Care Medicine recommends obtaining at least 2 sets of blood cultures (aerobic and anaerobic) before antibiotics when sepsis is suspected, with specific indications including fever, chills, hypothermia, leukocytosis, left-shift neutrophils, neutropenia, hypoalbuminemia, new renal failure, or hemodynamic compromise 2, 5, 6
Elevated lactate >1 mmol/L indicates tissue hypoperfusion, and serial measurements guide resuscitation effectiveness 2

Procalcitonin (PCT) levels ≥1.5 ng/mL have 100% sensitivity and 72% specificity for sepsis in ICU patients, and rises more quickly than CRP and correlates more closely with sepsis severity 5, 6
C-Reactive Protein (CRP) levels ≥50 mg/L have 98.5% sensitivity and 75% specificity for probable/definite sepsis, but is less specific than PCT 5, 6

The National Health Service recommends re-calculating NEWS2 score at intervals based on risk level: every 30 minutes for high risk, every hour for moderate risk, every 4-6 hours for low risk, and per routine protocol for very low risk 1, 3

The National Health Service advises always interpreting NEWS2 in context of patient's baseline physiology and comorbidities, clinical trajectory, and response to interventions 1, 3
The Society of Critical Care Medicine notes that NEWS2 may underestimate risk when condition is deteriorating despite interventions, patient has not improved since previous assessment, or certain high-risk clinical signs are present 1, 2, 6