What labs should be ordered in suspected sepsis?

Essential Laboratory Tests for Suspected Sepsis

In suspected sepsis, obtain blood cultures (at least two sets), complete blood count, comprehensive metabolic panel, lactate, coagulation studies, and procalcitonin immediately before starting antimicrobial therapy, provided this does not delay antibiotic administration beyond one hour. 1

Initial Laboratory Workup

Microbiological Cultures

• Obtain 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
• Ensure blood cultures are collected within 45 minutes to avoid delaying antibiotic administration 2
• Consider cultures from other potential infection sources based on clinical presentation (urine, sputum, wound, etc.) 3

Essential Laboratory Tests

• Complete blood count (CBC) to assess for leukocytosis, leukopenia, or bandemia 1
• Comprehensive metabolic panel to evaluate organ function and electrolyte abnormalities 1
• Serum lactate level (elevated levels >2 mmol/L indicate more severe disease and need for aggressive resuscitation) 1, 4
• Coagulation studies (PT/INR, PTT) to assess for coagulopathy 1
• Procalcitonin as an adjunctive test to assist in determining likelihood of bacterial infection 1, 5
• C-reactive protein (CRP) - levels ≥50 mg/L have demonstrated 98.5% sensitivity and 75% specificity for identifying probable sepsis 3, 2

Monitoring and Follow-up Testing

• Serial lactate measurements to guide resuscitation and assess response to therapy 1
• Follow-up blood cultures to document clearance of bacteremia 3
• Daily reassessment of organ function parameters to track progression or resolution 1
• Monitor coagulation parameters for development of sepsis-induced coagulopathy 2

Risk Stratification Tools

• Use NEWS2 (National Early Warning Score 2) to evaluate risk of severe illness or death from sepsis 3
• Consider a score of 7 or more as indicating high risk of severe illness or death 3
• A score of 5 or 6 suggests moderate risk of severe illness or death 3
• A score of 3 in any single parameter may indicate increased risk from sepsis 3

Special Considerations

• In patients with suspected septic shock, prioritize obtaining lactate levels as part of the definition of septic shock includes lactate >2 mmol/L 1, 4
• For patients with suspected cardiac involvement, consider bedside cardiac ultrasonography to evaluate for LV or RV dysfunction 3
• PCT has higher diagnostic accuracy than CRP for sepsis diagnosis (area under ROC curve of 0.85 vs. 0.73) 2
• Traditional markers like neutrophilia alone lack sufficient sensitivity to distinguish sepsis in hospitalized patients 3

Interpretation Caveats

• No single laboratory test can accurately diagnose sepsis 4
• Biomarkers should be interpreted in the context of clinical presentation 5
• Consider pre-existing conditions that may affect baseline laboratory values 3
• Interpret NEWS2 scores in the context of the person's underlying physiology and comorbidities 3
• Recognize that negative cultures do not exclude sepsis, especially in patients who have received prior antibiotics 3

Remember that while laboratory tests are crucial for diagnosis and management, they should not delay the administration of appropriate antimicrobial therapy, which should be given within one hour of recognition of sepsis or septic shock 1.