Diagnosis of Sepsis in Adults
Sepsis is diagnosed when a patient has suspected or confirmed infection PLUS life-threatening organ dysfunction, operationalized as an increase in Sequential Organ Failure Assessment (SOFA) score of ≥2 points, which corresponds to >10% in-hospital mortality risk. 1, 2, 3
Core Diagnostic Framework
Step 1: Identify Suspected Infection
Perform detailed history and clinical examination to identify the infection source 4. The most common sources are:
- Respiratory (pneumonia is the most common cause) 5
- Gastrointestinal
- Genitourinary
- Skin and soft tissue
Step 2: Assess for Organ Dysfunction
Use the SOFA score increase of ≥2 points from baseline to confirm organ dysfunction 1, 3. This is the gold standard for sepsis diagnosis.
For rapid bedside screening, use qSOFA (quickSOFA) - award 1 point for each 1, 2, 3:
- Respiratory rate ≥22/min
- Altered mental status (Glasgow Coma Score ≤14)
- Systolic blood pressure ≤100 mmHg
If qSOFA ≥2 points: high suspicion for sepsis with poor outcomes - proceed immediately to full SOFA assessment and treatment 3.
Step 3: Risk Stratification with NEWS2
Calculate NEWS2 score to determine urgency of intervention 6. This 2024 NICE guidance provides the most current approach to stratifying risk of severe illness or death, directly informing the time window for antibiotic administration.
Step 4: Identify Septic Shock (if applicable)
Septic shock is diagnosed when sepsis is present PLUS both 1, 2, 3:
- Vasopressor requirement to maintain MAP ≥65 mmHg
- Serum lactate >2 mmol/L (>18 mg/dL) despite adequate fluid resuscitation
This combination carries >40% hospital mortality 3.
Essential Diagnostic Workup
Laboratory Tests
- Blood cultures (before antibiotics if possible, but don't delay treatment) 4, 5
- Serum lactate - elevated lactate (>2 mmol/L) indicates tissue hypoperfusion and is part of septic shock definition 1, 2, 5
- Procalcitonin - useful sepsis biomarker 5
- Complete blood count with differential
- Creatinine, liver function tests
- Coagulation studies
Imaging Studies
CT scan is the imaging modality of choice for adults not undergoing immediate laparotomy to determine infection source 7. For suspected thoracic sepsis, CT chest with IV contrast has 81.82% positive predictive value for identifying septic foci, particularly pneumonia 8.
Skip imaging if patient has obvious diffuse peritonitis requiring immediate surgery 7.
Source Identification
Sample fluid or tissue from suspected infection site when possible without harming the patient. Examine by Gram stain, culture, and antibiogram 4.
Clinical Manifestations to Recognize
Beyond vital sign abnormalities, look for signs of tissue hypoperfusion 4, 1:
- Altered mental status (most frequently cited indicator)
- Mottled skin or delayed capillary refill time
- Cold, clammy extremities
- Decreased urine output (<0.5 mL/kg/hr in adults)
- Weak peripheral pulses
Critical Pitfalls
The clinical presentation can be subtle, particularly in:
- Older patients 5
- Immunocompromised patients 5
- Patients without obvious signs (20% of septic patients) - these patients experience delayed antibiotic administration, higher ICU admission rates (43.8%), and increased mortality (14.7%) 9
Don't rely solely on fever - sepsis can present with hypothermia (<36°C) 1.
Don't wait for hypotension - organ dysfunction defines sepsis, not blood pressure alone. One guideline explicitly states hypotension is not required for shock diagnosis if clinical findings and lactate >2 mmol/L are present 1.
Emerging Evidence
Recent 2026 research suggests combining qSOFA with lactate (qSOFA-lactate score) modestly improves risk stratification (AUROC 0.724 vs 0.706 for qSOFA alone), with particular utility for nurse-led assessments 10. However, this remains investigational and the standard SOFA/qSOFA approach per Sepsis-3 definitions should guide practice.
The key is early recognition - once sepsis is suspected or diagnosed, treatment must begin immediately, as delays directly correlate with worse outcomes 9.