Bacterial Sepsis Workup

Updated: Feb 03, 2023
  • Author: Amber Mahmood Bokhari, MBBS; Chief Editor: Michael Stuart Bronze, MD  more...
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Approach Considerations

Multiple clinical, laboratory, radiologic, and microbiologic data are required for the diagnosis of sepsis and septic shock. Sepsis should never be diagnosed based on a single abnormality. However, the diagnosis is often made empirically at the bedside upon presentation or retrospectively when follow-up data return (eg, positive blood culture result) or a response to antibiotics is evident. Importantly, the identification of a pathogenic organism, although preferred, is not always feasible since the responsible organism may be unidentified in many patients.

In general, the workup for sepsis may include the following:

  • Blood culture and urine analysis and culture
  • Chemistry studies that can suggest organ dysfunction, such as liver or kidney function tests
  • Serum lactate levels obtained urgently and serially.
  • Chest radiology
  • Diagnostic imaging of the chest and abdomen/pelvis
  • Cardiac studies such as ECG and troponins, as indicated
  • Interventions such as paracentesis, thoracentesis, lumbar puncture, or aspiration of an abscess, as clinically indicated
  • Measurement of biomarkers of sepsis such as procalcitonin levels

Laboratory Studies

Complete blood cell count

A complete blood cell (CBC) count is usually not specific. Leukocytosis with a left shift is also a nonspecific diagnostic finding and can be seen in noninfectious conditions. Leukopenia, anemia, and thrombocytopenia may be observed in sepsis.

Complete metabolic profile

A complete metabolic profile identifies changes in organ function, especially the liver and kidneys.

Bacterial cultures

Obtain blood cultures in all patients upon admission. Negative blood culture results are also necessary to include pseudosepsis in the differential diagnosis. [44] Blood culture isolates might suggest the underlying disease process. Bacteroides fragilis suggests a colonic or pelvic source, whereas Klebsiella species or enterococci suggest a gallbladder or urinary tract source.

If central intravenous (IV) line sepsis is suspected, remove the line and send the tip for semiquantitative bacterial culture. If culture of the catheter tip yields positive results and demonstrates 15 or more colonies and if the isolate from the tip matches the isolate from the blood culture, an infection associated with the central IV line is diagnosed.

ICU patients are at a greater risk for colonization by MRSA, vancomycin-resistant enterococci (VRE), and carbapenem-resistant Enterobacteriaceae (CRE). It is critical to deescalate or change the empiric antibiotic regimen once the organism susceptibilities are available.

Gram staining

Buffy coat analysis of CBC may be useful in identifying certain infectious agents, although the yield is low. [45]

Urinalysis with reflex to culture

If urosepsis is suspected, obtain a urine Gram stain, urinalysis, and urine culture. A systematic review found that in adult ICU patients, catheter-associated urinary tract infection was associated with significantly higher mortality and a longer stay. [46]


Organism identification via culture in a patient who fulfills the definition of sepsis is highly supportive of a sepsis diagnosis but is unnecessary. The rationale behind its lack of inclusion in the diagnostic criteria for sepsis is that a culprit organism goes unidentified in up to half of patients who present with sepsis, and a positive culture result is not required to make a decision regarding treatment with empiric antibiotics.

Unique laboratory findings

Laboratory and clinical features that may suggest an underlying etiology of sepsis are as follows:

  • Leukocytosis (WBC count >12,000/µL) or leukopenia (WBC count < 4000/µL)
  • Normal WBC count with greater than 10% immature forms (left shift with bandemia)
  • Hyperglycemia (plasma glucose level >140 mg/dL or 7.7 mmol/L) in the absence of diabetes [25]
  • Plasma C-reactive protein level of more than 2 standard deviations above the reference value
  • Arterial hypoxemia (PaO 2/FiO 2 ratio < 300 mm Hg)
  • Acute oliguria (urine output < 0.5 mL/kg/hour for at least 2 hours despite adequate fluid resuscitation)
  • Creatinine increase >0.5 mg/dL or 44.2 mmol/L
  • Coagulation abnormalities (INR >1.5 or PTT >60 seconds)
  • Thrombocytopenia (platelet count < 100,000/µL) [24]
  • Hyperbilirubinemia (plasma total bilirubin >4 mg/dL or 70 mmol/L)
  • Adrenal insufficiency (eg, hyponatremia, hyperkalemia) and euthyroid sick syndrome can also be found in sepsis.
  • Hyperlactatemia (serum lactate >2 mmol/L) can result from organ hypoperfusion in the presence or absence of hypotension and indicates a poor prognosis. A serum lactate level of 4 mmol/L or more (especially arterial lactate) indicates septic shock.
  • Plasma procalcitonin and presepsin elevation is associated with bacterial infection and sepsis. [7, 8, 9, 10]

Procalcitonin levels

Procalcitonin (PCT) is an acute-phase reactant that is elevated in severe bacterial infections. In most clinical assays, the reference range of PCT is below detectable. Measurement of PCT and C-reactive protein (CRP) at onset and on the fourth day of treatment can predict survival of patients with ventilator-associated pneumonia. A decrease in either one of these marker values predicts survival. [9]

A study from van Nieuwkoop et al examined the use of PCT levels in predicting bacteremia in a group of 581 patients, 136 of whom had bacteremia; PCT levels successfully identified 94-99% of the patients with bacteremia. [7]

Heyland et al, in a systematic review of the economic value of PCT-guided reduction in antibiotic use in intensive care, found that with hospital mortality and length of stay unchanged, PCT testing to reduce antibiotic treatment broke even when daily antibiotics cost about $150 in Canadian dollars. [8]


Chest Radiology and Chest CT Scan

Chest Radiography

No radiologic signs are specific to the identification of sepsis, but chest radiography can aid in identifying a specific infection site. Chest radiography is important to rule out pneumonia and diagnose other causes of pulmonary infiltrates, such as the following:

  • Pulmonary drug reactions
  • Pulmonary embolism
  • Pulmonary hemorrhage
  • Primary or metastatic pulmonary neoplasms
  • Lymphangitic spread of malignancies
  • Large pleural effusions
  • Pneumothorax
  • Hydrothorax
  • Fluid overload
  • Congestive heart failure (CHF)
  • Acute myocardial infarction (MI)
  • Acute respiratory distress syndrome

Chest CT Scanning

Chest CT scanning is a very sensitive modality for diagnosing the lung pathology listed above.


Abdominal Ultrasonography, CT Scanning, and MRI

Perform abdominal ultrasonography if biliary tract obstruction is suspected based on the clinical presentation. However, abdominal ultrasonography is suboptimal for the detection of abscesses or perforated hollow organs. Ultrasonograms in patients with cholecystitis may show a thickened gallbladder wall or biliary calculi but no dilatation of the common bile duct (CBD). Stones in the biliary tract may or may not be visible in patients with cholangitis, but the CBD typically is dilated. [47]

Use computed tomography (CT) or magnetic resonance imaging (MRI) of the abdomen if a nonbiliary intra-abdominal source of infection is suspected on the basis of the history or physical examination findings. Abdominal CT or MRI is also helpful in delineating intrarenal and extrarenal pathology. Gallium or indium scanning has no place in the initial workup of sepsis; patients with sepsis are acutely ill by definition, and rapid diagnostic tests (eg, CT or MRI of the abdomen and ultrasonography of the right upper quadrant) are time-critical, life-saving tools. However, MRI is more time consuming than CT scanning, and the latter is preferred in emergent situations. [47]


Cardiac Studies

If acute MI is likely, perform electrocardiography (ECG) and obtain cardiac enzyme levels. Remember that certain patients may present with a silent, asymptomatic MI, which should be included in the differential diagnosis of otherwise unexplained fever, leukocytosis, and hypotension. Silent MIs are common in elderly patients and in those who have recently undergone abdominal or pelvic surgical procedures. They are also common in individuals with alcoholism, diabetes, and uremic conditions.

The following cardiac studies may be useful if cardiac involvement or disease is suspected as a cause or complication of infection:

  • Electrocardiography (ECG) to evaluate for conduction abnormalities or delays or arrhythmias
  • Cardiac enzyme levels
  • Echocardiography to evaluate for structural heart disease

Invasive Interventions

Invasive diagnostic procedures that may be considered are discussed below.


Perform thoracentesis for diagnostic purposes in patients with substantial pleural effusion. Perform paracentesis in patients with gross ascites.

Surgical incision and drainage

Drainage of fluid collections/abscesses is crucial in establishing good source control and in facilitating a good clinical response to subsequent antibiotic therapy.


Bronchoscopy with washing, lavage, or other invasive sampling is performed in patients with suspected pneumonia and in patients with suspected invasive fungal infections of the lung.

Swan-Ganz catheterization

In highly selected cases, a Swan-Ganz catheter may be useful in managing the fluid status of the patient and in assessing left ventricular dysfunction; however, routine use is not recommended.


Imaging Studies

Site-specific soft tissue imaging includes ultrasonography, CT scanning, or MRI to assess for possible abscess, fluid collection, or necrotizing skin infection. These are essential for diagnostic purposes and for monitoring the response to therapy.

Contrast-enhanced CT scanning or MRI of the brain/neck is performed to assess for possible masses, abscess, fluid collection, or necrotizing infection.