Laboratory Tests for Sepsis Workup
Blood cultures and lactate measurement are the most essential laboratory tests for sepsis workup, followed by complete blood count, comprehensive metabolic panel, and coagulation studies. 1, 2
Core Laboratory Tests
Blood cultures: Obtain at least two sets (aerobic and anaerobic bottles) before starting antimicrobial therapy, with at least one drawn percutaneously and one through each vascular access device (if present for >48 hours), provided this does not significantly delay antibiotic administration (>45 minutes) 2
Serum lactate: Critical for assessing tissue perfusion and disease severity; elevated levels (>2 mmol/L) indicate more severe disease requiring aggressive resuscitation 1, 2
Complete blood count (CBC): Essential to assess for leukocytosis, leukopenia, or bandemia, which can indicate infection and sepsis 1, 3
Comprehensive metabolic panel: Necessary to evaluate organ function, electrolyte abnormalities, and acid-base status 1
Coagulation studies: Important to assess for coagulopathy, which may indicate more severe disease and development of septic shock 1
Additional Recommended Tests
Cultures from suspected sources of infection: Obtain cultures from potential infection sites (urine, cerebrospinal fluid, wounds, respiratory secretions) before antimicrobial therapy if doing so does not delay antibiotic administration 2
Procalcitonin: Can be considered as an adjunctive test to assist in determining the likelihood of bacterial infection and potentially guide antibiotic discontinuation 1, 4
C-reactive protein: May help monitor inflammatory response, though not specific for sepsis 4
Special Considerations
Fungal infection biomarkers: Consider 1,3-β-D-glucan assay, mannan and anti-mannan antibody assays when invasive candidiasis is in the differential diagnosis 2
Molecular diagnostic tests: Rapid, non-culture-based diagnostic methods (PCR, mass spectroscopy) may be helpful for quicker identification of pathogens, especially for difficult-to-culture organisms or when antimicrobials have already been administered 2, 5
Timing and Implementation
Critical timing: Blood cultures and other laboratory tests should be obtained within 3 hours of sepsis recognition, but should not delay antimicrobial administration beyond 1 hour 2
Blood culture technique: Proper collection technique is essential to minimize contamination; studies show that paramedics can obtain uncontaminated blood cultures in the field with a 95% success rate 6
Blood volume: Collect at least 1 mL of blood for cultures to ensure adequate sensitivity 7
Imaging Studies
Prompt imaging: Perform imaging studies promptly to identify potential sources of infection requiring drainage or surgical intervention 2
Bedside studies: Consider bedside ultrasound to avoid patient transport when appropriate 2
Pitfalls and Caveats
Blood culture limitations: Blood cultures are positive in only about 30% of septic patients; negative cultures do not rule out sepsis 5
Biomarker interpretation: No single biomarker can definitively diagnose sepsis; clinical context is essential 4
Contamination risk: Improper blood culture collection technique can lead to false positives; proper skin preparation and sterile technique are crucial 6
Delayed results: Traditional culture methods may take 24-72 hours for results; this should not delay empiric antimicrobial therapy 2
Pre-antibiotic cultures: Obtaining cultures after antimicrobial administration significantly reduces yield; always attempt to obtain cultures before antibiotics when possible 2