What are the components of a septic workup for a patient with suspected sepsis?

Septic Workup Components

A comprehensive septic workup requires immediate blood cultures, lactate measurement, complete blood count, comprehensive metabolic panel, and targeted imaging with CT (not plain radiography alone) to identify the infection source, all obtained within the first hour while simultaneously initiating resuscitation and antimicrobials. 1, 2

Immediate Laboratory Studies (Within First Hour)

Blood Cultures

• Obtain at least 2 sets of blood cultures (aerobic and anaerobic bottles) before antimicrobials if this causes no substantial delay (>45 minutes) 1, 2
• Draw at least one set percutaneously and one through each vascular access device (unless inserted <48 hours ago) 1, 2
• Blood cultures are indicated when any of the following are present: fever, chills, hypothermia, leukocytosis, left-shift of neutrophils, neutropenia, hypoalbuminemia, development of renal failure, signs of hemodynamic compromise, or diagnosis of urinary tract infection 3

Lactate Measurement

• Measure serum lactate immediately to assess tissue hypoperfusion 2
• Elevated lactate (≥4 mmol/L) defines sepsis-induced tissue hypoperfusion requiring aggressive resuscitation 2
• Recheck lactate every 2-6 hours during acute resuscitation, targeting normalization as a marker of adequate tissue perfusion 2

Complete Blood Count

• Check for leukocytosis (WBC >12,000/μL), leukopenia (WBC <4,000/μL), or normal WBC with >10% immature forms (bandemia) 3
• Assess for neutropenia or left-shift of neutrophils 3

Comprehensive Metabolic Panel

• Assess baseline renal function (creatinine, eGFR) 2
• Check electrolytes, particularly sodium 2
• Measure albumin (hypoalbuminemia correlates with bacteremia) 2
• Check bilirubin (>2 mg/dL indicates hepatic dysfunction) 3

Coagulation Studies

• Measure platelets (<100,000/μL) and INR (>1.5) to assess coagulation dysfunction 3

Biomarker Testing

Procalcitonin (PCT)

• PCT ≥1.5 ng/mL has 100% sensitivity and 72% specificity for sepsis in ICU patients 1, 3
• PCT rises within 4 hours of bacterial exposure, peaks at 6-8 hours 1
• PCT correlates with sepsis severity and predicts mortality 1
• Caveat: PCT and CRP cannot alone differentiate sepsis from other causes of SIRS; they are part of a systematic evaluation that includes clinical examination and directed diagnostic techniques 4, 1

C-Reactive Protein (CRP)

• CRP ≥50 mg/L has 98.5% sensitivity and 75% specificity for identifying probable or definite sepsis 1, 3
• CRP rises 12-24 hours after inflammatory insult, peaks at 48 hours 1
• Daily, sequential measurement of inflammatory markers is more valuable than single measurements 4

Imaging for Source Identification

Respiratory Source

• Do not rely on chest radiography alone - sensitivity for pneumonia in severe sepsis/septic shock is only 58% 3
• If chest X-ray is normal/equivocal but suspicion remains high, proceed immediately to CT chest with IV contrast 1
• CT chest with IV contrast identifies infectious source in 72% of cases and changes management in 45% 4, 1
• The chest is the most common septic focus location (38.6% of cases) 3

Abdominal/Pelvic Source

• CT abdomen/pelvis with IV contrast has 81.82% positive predictive value for identifying septic foci 4, 3
• Abdomen (22.0%) and pelvis/genitourinary tract (20.5%) are the second and third most common septic foci locations 4, 3
• For suspected urosepsis, obtain abdominal ultrasound first due to portability and rapid acquisition 3
• If ultrasound is negative or equivocal, proceed immediately to CT abdomen/pelvis with IV contrast 3

FDG-PET/CT for Unknown Source

• When initial workup including chest radiography is unrevealing, FDG-PET/CT identifies infection source in 66-78% of cases 4
• FDG-PET/CT changes management in 25-33% of patients (surgery, drainage catheter placement, antibiotic modification) 4
• FDG-PET/CT has 90.9% sensitivity, 87.5% specificity, 95.2% PPV, and 77.8% NPV for identifying infection focus 4

Focused Physical Examination

Specific Sites to Examine

• Inspect vascular access sites for phlebitis or cellulitis 4, 2
• Examine surgical and traumatic wounds for signs of infection 4
• Check pressure areas and injection sites for soft tissue infection 4
• Assess for sinusitis 4
• Perform fundoscopy to detect candidal endophthalmitis (pathognomonic for systemic fungal sepsis) 4
• Examine urine in catheter for purulent appearance 4
• Assess for diarrhea indicating possible Clostridium difficile colitis 4

Microbiological Sampling

Specimen Collection

• Sample fluid or tissue from the suspected site of infection in a sterile fashion whenever possible and without harm to the patient 4
• Collect samples before initiation of empirical antimicrobial therapy to maximize sensitivity of microbiological cultures 4

Laboratory Processing

• Perform Gram stain and microscopic examination whenever applicable 4
• Culture specimens and assess antibiotic susceptibility to locally available antibiotics for targeted antimicrobial therapy 4
• In endemic areas, perform specific tests for parasitic infections (e.g., thick smear for malaria) 4

Hemodynamic Monitoring

• Target mean arterial pressure (MAP) ≥65 mmHg with vasopressors if needed 2
• Target central venous oxygen saturation ≥70% (superior vena cava) or ≥65% (mixed venous) if available 2
• Monitor urine output (oliguria: <0.5 mL/kg/h for ≥2 hours indicates renal dysfunction) 3

Critical Pitfalls to Avoid

• Never wait for culture results before diagnosis - sepsis is a clinical diagnosis and cultures should not delay treatment 1
• Never rely on a single biomarker - use comprehensive clinical assessment 1
• Never use chest X-ray alone when clinical suspicion is high - proceed directly to CT with IV contrast 1, 3
• Never delay blood cultures beyond 45 minutes to start antimicrobials 1, 2