Gastrointestinal Imaging

What Is the Best Next Scan for Sepsis with a Normal Chest Radiograph?

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What Is the Best Next Scan for Sepsis with a Normal Chest Radiograph?

It’s 2 a.m. in the emergency department, and your patient meets sepsis criteria. They are febrile, tachycardic, and have an elevated lactate, but they are unable to provide a clear history. You’ve initiated fluid resuscitation and broad-spectrum antibiotics. The initial workup, including a portable chest radiograph, is complete. The radiograph comes back as normal or nonspecific, offering no clue to the source of the infection. The patient isn’t improving, and you know the most common sources of sepsis are the lungs, abdomen, and urinary tract. With the lungs provisionally cleared, the abdomen and pelvis are the next logical place to look. This article details the American College of Radiology (ACR) Appropriateness Criteria for this exact scenario: suspected sepsis of unknown origin after a non-diagnostic chest radiograph. For this presentation, the ACR rates CT abdomen and pelvis with IV contrast as Usually appropriate.

Who Fits This Clinical Scenario?

This guidance applies to a specific, and often challenging, patient population: adults with suspected or confirmed sepsis where the source is not clinically apparent. The key inclusion criteria are:

  • The patient meets clinical criteria for sepsis (e.g., per Sepsis-3 guidelines).
  • There are no localizing symptoms or signs (e.g., no specific abdominal pain, no productive cough, no dysuria) pointing to a source. This also includes patients who cannot provide a history due to altered mental status, intubation, or other communication barriers.
  • An initial chest radiograph has been performed and is interpreted as normal, equivocal, or showing only nonspecific findings like atelectasis.

It is crucial to distinguish this situation from similar presentations. This workflow does not apply if:

  • The patient has clear abdominal symptoms. A patient with sepsis and acute, localized abdominal pain falls under a different ACR variant, which may alter the initial imaging choice or pre-test probability.
  • The patient has clear pulmonary symptoms. If the primary symptoms are cough, dyspnea, or chest pain, the imaging workup is focused on the chest, even if the initial radiograph is normal. This follows a separate diagnostic pathway.
  • No initial imaging has been performed. This guidance is for the next imaging study after an unrevealing chest radiograph, not the first-line imaging choice from scratch.

What Diagnoses Are You Working Up in This Scenario?

When the lungs are an unlikely source, the search for an occult infection pivots to the abdomen and pelvis, which harbor many potential culprits. The differential diagnosis in this context is broad, but the imaging search is focused on identifying conditions that are both common and require urgent intervention, such as drainage or surgery.

Intra-abdominal Abscess: This is a primary concern. An abscess can arise from numerous sources, with diverticulitis and appendicitis being among the most common. A perforated viscus, recent surgery, or inflammatory bowel disease can also lead to contained fluid collections that seed the bloodstream. These are often clinically silent until the patient becomes systemically ill.

Complicated Urinary Tract Infection: While simple cystitis rarely causes sepsis in healthy adults, complicated infections like pyelonephritis, renal or perinephric abscess, or an obstructed and infected urinary system are significant causes. These are particularly common in older adults and those with comorbidities like diabetes or urinary tract abnormalities.

Hepatobiliary Infection: Acute cholecystitis, and especially the more severe ascending cholangitis, can present insidiously with sepsis but without classic right upper quadrant pain, particularly in elderly or critically ill patients (acalculous cholecystitis). A liver abscess is another important, though less common, consideration.

Bowel Ischemia or Perforation: A catastrophic vascular event like mesenteric ischemia or a subtle (“micro”) perforation of the bowel can present as sepsis with diffuse or absent abdominal signs. These are time-critical diagnoses where imaging can be life-saving.

Why Is CT Abdomen and Pelvis with IV Contrast the Recommended Study?

For a septic patient without a clear source and a normal chest radiograph, the ACR designates CT abdomen and pelvis with IV contrast as Usually appropriate. This recommendation is based on the modality’s high diagnostic yield for the critical pathologies in the differential diagnosis.

The key to this study’s effectiveness is intravenous contrast. IV contrast enhances the visibility of inflammation, vascularity, and organ perfusion. It is essential for delineating the enhancing rim of an abscess, identifying areas of poor perfusion in bowel ischemia, and highlighting inflammatory changes in the kidneys, gallbladder wall, or pancreas. A non-contrast study would obscure or completely miss many of these findings.

Compared to other modalities, CT provides a rapid, comprehensive assessment of the solid organs, the bowel, the vasculature, and the retroperitoneum. Its high spatial resolution is excellent for detecting small fluid collections, subtle bowel wall thickening, and perinephric fat stranding indicative of pyelonephritis.

Let’s consider the alternatives and why they are rated lower for this specific scenario:

  • US abdomen is rated May be appropriate. While it uses no ionizing radiation and is excellent for evaluating the gallbladder and kidneys, it is often limited by the patient’s body habitus and overlying bowel gas. It provides a poor evaluation of the bowel and retroperitoneum, making it an incomplete screening tool for an unknown source of sepsis.
  • CT abdomen and pelvis without IV contrast is rated May be appropriate (Disagreement). The lack of IV contrast is a major limitation. While it can identify free air, calcified gallstones, or kidney stones causing obstruction, it cannot reliably diagnose abscesses, pyelonephritis, cholecystitis, or bowel ischemia. Its use is generally reserved for patients with a severe contraindication to IV contrast.

The recommended CT study carries a relative radiation level of ☢☢☢ (1-10 mSv). While radiation exposure is always a consideration, in the setting of life-threatening sepsis, the diagnostic benefit of identifying a treatable source overwhelmingly justifies the risk.

Once you’ve decided on a comprehensive torso scan, our protocol guide covers the technique, contrast, and reading principles: CT Chest/Abdomen/Pelvis with IV Contrast.

What’s Next After CT Abdomen and Pelvis with IV Contrast? Downstream Workflow

The results of the CT scan will guide your immediate next steps. The clinical workflow branches significantly based on whether the scan identifies a source.

If the CT is positive for a source: The finding dictates the subsequent consultation and intervention.

  • Finding: A drainable fluid collection or abscess (e.g., from diverticulitis).
    Next Step: Urgent consultation with Interventional Radiology for percutaneous drainage or General Surgery for surgical source control.
  • Finding: Complicated pyelonephritis or a renal abscess.
    Next Step: Consultation with Urology, especially if there is evidence of obstruction. Continue and tailor IV antibiotics based on culture data.
  • Finding: Bowel ischemia or perforation.
    Next Step: Immediate surgical consultation. This is a surgical emergency.

If the CT is negative: A negative high-quality CT of the abdomen and pelvis makes a source in this region much less likely, forcing a diagnostic pivot.

  • Next Step: Re-evaluate the patient for other sources. Is there a subtle skin or soft tissue infection? A line infection? Could this be endocarditis? Consider a CT of the chest with IV contrast if clinical suspicion for a pulmonary embolism or occult pneumonia remains despite the normal radiograph. Consider transthoracic or transesophageal echocardiography to evaluate for endocarditis.

If the CT is indeterminate: Occasionally, a finding is nonspecific. For example, diffuse non-obstructive bowel wall thickening could be infectious, ischemic, or inflammatory.

  • Next Step: Correlate closely with clinical and laboratory data (e.g., lactate). Further imaging with a different modality, like MRI for a suspected liver lesion, may be considered, but the immediate priority is continued resuscitation and supportive care while monitoring the patient’s clinical trajectory.

Pitfalls to Avoid (and When to Get Help)

In the high-stakes environment of managing a septic patient, several common pitfalls can delay diagnosis and treatment.

  • Omitting IV Contrast: Ordering a non-contrast CT to “save the kidneys” in a patient with mild chronic kidney disease severely compromises the diagnostic utility of the scan. Discuss the risk/benefit profile with the radiology team; the risk of missing a life-threatening abscess often outweighs the risk of contrast-induced nephropathy.
  • Delaying the Scan: Sepsis is a time-sensitive condition. Once the decision to image is made, it should be performed emergently. Delays for non-critical reasons can lead to worse outcomes.
  • Satisfaction of Search: If the CT is negative, do not stop looking for a source. A negative scan of one body cavity is not a clean bill of health. Re-examine the patient from head to toe for overlooked sources like cellulitis, decubitus ulcers, or septic arthritis.

If the patient continues to decline despite a negative workup and broad-spectrum antibiotics, escalate care by involving critical care specialists and infectious disease consultants early.

Related ACR Topics and Tools

This article focuses on one specific clinical workflow. For a comprehensive overview of imaging in all sepsis-related scenarios, from initial presentation to follow-up, please consult our parent guide. Additional GigHz tools can help you apply these criteria and understand the technical details of the recommended studies.

Frequently Asked Questions

Why not just order a CT of the chest, abdomen, and pelvis (a ‘pan-scan’) on every septic patient without a source?

While a CT of the chest, abdomen, and pelvis with IV contrast is rated as *May be appropriate (Disagreement)* by the ACR, it involves a higher radiation dose (☢☢☢☢ 10-30 mSv) than a targeted CT of the abdomen and pelvis. The scenario specifies that an initial chest radiograph was already performed and was non-diagnostic. Therefore, the ACR guidance prioritizes the highest-yield next study, which is the abdomen/pelvis. A chest CT can be added if clinical suspicion shifts back to the thorax, but starting with a targeted study is a more judicious use of radiation.

What if my patient has severe renal failure and absolutely cannot receive IV contrast?

This is a challenging situation where no imaging test is perfect. A CT of the abdomen and pelvis without IV contrast is an option, rated *May be appropriate (Disagreement)*. It can identify some critical findings like free air, bowel obstruction, or calcified stones, but it is insensitive for abscesses and ischemia. An alternative is an abdominal ultrasound, which is *May be appropriate* and can assess the kidneys and gallbladder well. In some cases, an MRI of the abdomen and pelvis without contrast may be considered, but it is time-consuming and less available emergently. This decision requires a careful discussion of risks and benefits with the radiology team.

Is ultrasound a reasonable first choice to avoid radiation?

Ultrasound of the abdomen is rated *May be appropriate*. It is an excellent, radiation-free tool for specific questions, such as ruling out cholecystitis or hydronephrosis. However, as a general screening tool for an unknown source of sepsis, it is limited. Bowel gas and patient body habitus can obscure the pancreas, retroperitoneum, and much of the bowel. If your pre-test suspicion for a biliary or renal source is very high, it can be a reasonable first step, but CT is generally the more comprehensive and definitive test in this undifferentiated scenario.

The chest radiograph was ‘equivocal.’ Should I get a CT chest instead of abdomen/pelvis?

This depends on the nature of the equivocal finding and the overall clinical picture. If the radiologist notes a vague opacity that could represent an early pneumonia and the patient has any subtle respiratory signs, then a CT chest with IV contrast (*May be appropriate*) would be a logical next step. However, if the ‘equivocal’ finding is something like mild atelectasis in a patient with no respiratory symptoms, the abdomen and pelvis remain the higher-yield location to investigate for an occult source of sepsis.

What if the CT abdomen/pelvis is negative but the patient is still septic?

A negative CT is a crucial piece of information that significantly lowers the probability of an intra-abdominal source. The workup must then expand. Re-examine the patient for missed physical findings (e.g., skin/soft tissue infection, septic joint). Consider less common sources that are not well-visualized on CT, such as endocarditis (requiring an echocardiogram) or meningitis (requiring a lumbar puncture). Consultation with infectious disease specialists is highly recommended at this stage.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026