How is sepsis clinically diagnosed?

Clinical Diagnosis of Sepsis

Sepsis is clinically diagnosed using the NEWS2 scoring system combined with suspected or confirmed infection, with a NEWS2 score ≥5 indicating moderate-to-high risk requiring immediate evaluation and intervention. 1

Diagnostic Algorithm

Step 1: Identify Suspected Infection

Look for clinical evidence of infection from any source:

• Most common sources: Respiratory (pneumonia is #1), gastrointestinal, genitourinary, skin/soft tissue 2
• History of recent infection or infectious symptoms
• Clinical signs pointing to an anatomic source

Step 2: Calculate NEWS2 Score

Use the NEWS2 tool to assess physiologic derangement across 7 parameters 1:

• Respiratory rate
• Oxygen saturation (with scale adjustment for hypercapnic patients)
• Supplemental oxygen requirement
• Systolic blood pressure
• Heart rate
• Level of consciousness (Alert vs. CVPU: Confusion/Voice/Pain/Unresponsive)
• Temperature

Step 3: Risk Stratification Based on NEWS2

Score interpretation 1:

• ≥7: High risk of severe illness or death from sepsis
• 5-6: Moderate risk
• 1-4: Low risk
• 0: Very low risk

Critical caveat: A score of 3 in any single parameter may indicate increased sepsis risk even if total score is low 1

Step 4: Clinical Override Indicators

Immediately escalate risk assessment if any of these are present, regardless of NEWS2 score 1:

• Mottled or ashen appearance
• Non-blanching petechial or purpuric rash
• Cyanosis of skin, lips, or tongue

Also escalate if the patient's condition is deteriorating or not improving despite interventions 1.

Step 5: Interpret in Clinical Context

Adjust interpretation based on 1:

• Underlying physiology and comorbidities
• Older patients may present subtly 2
• Immunocompromised patients may lack typical fever response 2

Diagnostic Workup

Once sepsis is suspected clinically, obtain:

Microbiologic cultures 3:

• At least 2 sets of blood cultures (aerobic and anaerobic)
• One drawn percutaneously, one through vascular access (if device >48 hours old)
• Obtain before antibiotics if this causes no substantial delay

Laboratory markers 2:

• Serum lactate (elevated lactate now incorporated into septic shock definition)
• Procalcitonin (PCT >1 ng/mL supports sepsis diagnosis, particularly with positive cultures)
• Basic labs including CBC, renal function, liver function

Imaging studies 3:

• Perform promptly to confirm suspected infection source

Monitoring Frequency After Diagnosis

Re-calculate NEWS2 and reassess 1:

• Every 30 minutes for high-risk patients (NEWS2 ≥7)
• Every hour for moderate-risk patients (NEWS2 5-6)
• Every 4-6 hours for low-risk patients (NEWS2 1-4)

Key Pitfalls to Avoid

1. Don't wait for fever: Clinical manifestations can be subtle, especially in elderly and immunocompromised patients 2

2. Don't ignore single-parameter elevation: A NEWS2 score of 3 in any single vital sign warrants concern even if total score is low 1

3. Don't delay cultures for antibiotics beyond 45 minutes: The balance is obtaining cultures without substantially delaying antimicrobials 3

4. Don't rely solely on bacteremia: Only 45% of sepsis syndrome patients are bacteremic 4; absence of positive blood cultures doesn't exclude sepsis

5. Context matters: Certain patient populations (older age, hypoxia, hypotension, renal insufficiency) are associated with both over- and underdiagnosis 5

The 2024 NICE guideline represents the most current approach 1, emphasizing structured NEWS2-based risk stratification over older definitions. This replaces previous SIRS-based criteria with a more physiologically grounded assessment tool that directly correlates with mortality risk.