What labs and tests are essential for diagnosing and managing sepsis?

Essential Labs and Tests for Diagnosing and Managing Sepsis

Blood cultures and lactate measurements are the cornerstone laboratory tests for diagnosing sepsis, and should be obtained before starting antimicrobial therapy as long as this does not delay antibiotic administration by more than 45 minutes. 1, 2

Initial Diagnostic Workup

Blood Tests

• Obtain at least two sets of blood cultures (both aerobic and anaerobic bottles) before starting antimicrobial therapy, with at least one drawn percutaneously and one drawn through each vascular access device 1, 2
• Measure serum lactate levels to assess tissue hypoperfusion and disease severity (levels >2 mmol/L indicate more severe disease requiring aggressive resuscitation) 1, 2
• Complete blood count to evaluate for leukocytosis, leukopenia, or bandemia 2
• Comprehensive metabolic panel to assess organ function and electrolyte abnormalities 2
• Coagulation studies (PT/INR, PTT) to evaluate for coagulopathy 2
• Procalcitonin can be used as an adjunctive test to assist in determining bacterial infection likelihood and potentially guide antibiotic discontinuation 1, 2

Source Identification Tests

• Urinalysis and urine culture if urinary source is suspected 3
• Respiratory cultures (sputum, tracheal aspirate) if respiratory source is suspected 1
• Cerebrospinal fluid analysis if meningitis is suspected 1
• Wound cultures if skin/soft tissue infection is present 1
• Consider 1,3-β-D-glucan assay and mannan/anti-mannan antibody tests if invasive candidiasis is suspected 1

Imaging Studies

• Prompt imaging studies should be performed to identify potential sources of infection requiring drainage or surgical intervention 1, 2
• Chest X-ray to evaluate for pneumonia 2
• Abdominal imaging (ultrasound, CT) if intra-abdominal source is suspected 2
• CT or MRI of specific regions based on clinical suspicion 2

Monitoring Parameters

Hemodynamic Monitoring

• Frequent vital sign measurements (heart rate, blood pressure, respiratory rate, temperature, oxygen saturation) 2
• Mean arterial pressure (target ≥65 mmHg) 1
• Urine output (target ≥0.5 mL/kg/hr) 1, 2
• Consider more advanced hemodynamic monitoring in patients not responding to initial therapy 1

Organ Function Assessment

• Sequential Organ Failure Assessment (SOFA) score to track organ dysfunction 2
• Serial lactate measurements to guide resuscitation and assess response to therapy 1, 2
• Daily assessment of renal and hepatic function 2

Timing Considerations

• Blood cultures should be obtained before antimicrobial therapy but should not delay antibiotic administration by more than 45 minutes 1
• Antimicrobial therapy should be administered within 1 hour of recognition of sepsis or septic shock 1, 3, 4
• Initial fluid resuscitation with 30 mL/kg of crystalloid should be given within the first 3 hours 1
• Reassessment of hemodynamic status should occur frequently after initial resuscitation 1

Common Pitfalls to Avoid

• Delaying antimicrobial therapy while waiting for culture results significantly increases mortality 3, 5
• Failure to obtain adequate blood cultures before starting antibiotics reduces the chance of identifying the causative pathogen 1, 2
• Inadequate source control despite appropriate antimicrobial therapy can lead to persistent infection 3
• Overreliance on a single parameter (such as lactate) without considering the full clinical picture 1, 2
• Failure to reassess antimicrobial regimen daily for potential de-escalation based on clinical improvement and culture results 1, 3

Special Considerations

• For pregnant patients, the same diagnostic approach applies, but lactic acid should not be used to diagnose sepsis during labor according to CMS guidance 1
• In immunocompromised patients, consider additional diagnostic tests for opportunistic pathogens 3
• For patients with suspected multidrug-resistant infections, broader initial antimicrobial coverage may be necessary 3

By following this systematic approach to laboratory and diagnostic testing in sepsis, clinicians can ensure timely diagnosis, appropriate treatment, and optimal outcomes for patients with this life-threatening condition.