Essential Laboratory Tests for Suspected Sepsis

Initial Laboratory Workup

• The American College of Physicians recommends obtaining at least two sets of blood cultures before starting antimicrobial therapy, with at least one drawn percutaneously and one through each vascular access device 1
• Blood cultures should be collected within 45 minutes to avoid delaying antibiotic administration, as recommended by the Infectious Diseases Society of America 2
• Consider cultures from other potential infection sources based on clinical presentation (urine, sputum, wound, etc.), as suggested by the Society of Critical Care Medicine 3
• A complete blood count (CBC) should be performed to assess for leukocytosis, leukopenia, or bandemia, according to the American College of Emergency Physicians 1
• A comprehensive metabolic panel should be used to evaluate organ function and electrolyte abnormalities, as recommended by the National Institute of General Medical Sciences 1
• Serum lactate level should be measured, with elevated levels >2 mmol/L indicating more severe disease and need for aggressive resuscitation, according to the Society of Critical Care Medicine 1
• Coagulation studies (PT/INR, PTT) should be performed to assess for coagulopathy, as suggested by the American College of Chest Physicians 1
• Procalcitonin can be used as an adjunctive test to assist in determining likelihood of bacterial infection, according to the Infectious Diseases Society of America 1
• C-reactive protein (CRP) levels ≥50 mg/L have demonstrated 98.5% sensitivity and 75% specificity for identifying probable sepsis, as reported by the Intensive Care Medicine journal 3

Monitoring and Follow-up Testing

• Serial lactate measurements should be performed to guide resuscitation and assess response to therapy, as recommended by the Society of Critical Care Medicine 1
• Follow-up blood cultures should be done to document clearance of bacteremia, according to the Infectious Diseases Society of America 3
• Daily reassessment of organ function parameters should be performed to track progression or resolution, as suggested by the American College of Physicians 1
• Coagulation parameters should be monitored for development of sepsis-induced coagulopathy, according to the American College of Chest Physicians 2

Risk Stratification Tools

• The National Institute for Health and Care Excellence recommends using NEWS2 (National Early Warning Score 2) to evaluate risk of severe illness or death from sepsis 4
• A NEWS2 score of 7 or more indicates high risk of severe illness or death, according to the Royal College of Physicians 4
• A score of 5 or 6 suggests moderate risk of severe illness or death, as reported by the BMJ journal 4
• A score of 3 in any single parameter may indicate increased risk from sepsis, according to the National Institute for Health and Care Excellence 4

Special Considerations

• In patients with suspected septic shock, lactate levels should be prioritized as part of the definition of septic shock includes lactate >2 mmol/L, as recommended by the Society of Critical Care Medicine 1
• For patients with suspected cardiac involvement, bedside cardiac ultrasonography can be used to evaluate for LV or RV dysfunction, according to the American College of Cardiology 5
• Procalcitonin has higher diagnostic accuracy than CRP for sepsis diagnosis (area under ROC curve of 0.85 vs. 0.73), as reported by the Praxis Medical Insights journal 2
• Traditional markers like neutrophilia alone lack sufficient sensitivity to distinguish sepsis in hospitalized patients, according to the Intensive Care Medicine journal 3

Interpretation Caveats

• Pre-existing conditions should be considered when interpreting laboratory values, as suggested by the American College of Physicians 3
• NEWS2 scores should be interpreted in the context of the person's underlying physiology and comorbidities, according to the National Institute for Health and Care Excellence 4
• Negative cultures do not exclude sepsis, especially in patients who have received prior antibiotics, as reported by the Infectious Diseases Society of America 3