Gastrointestinal Imaging

Sepsis with No Localizing Signs: Why a Chest Radiograph Is the ACR-Recommended First Step

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Sepsis with No Localizing Signs: Why a Chest Radiograph Is the ACR-Recommended First Step

It’s 2 a.m. in the emergency department, and you are evaluating an 82-year-old patient from a nursing facility with altered mental status. They are febrile to 39.1°C, tachycardic, and hypotensive, meeting criteria for septic shock. Due to delirium, the patient cannot provide a history, and a rapid physical exam reveals no obvious source of infection—no cough, no focal abdominal tenderness, no overlying skin changes. You need to locate the infectious source to guide therapy, but where do you start the imaging workup? This article details the clinical workflow for this exact scenario: suspected sepsis without localizing signs or symptoms. According to the American College of Radiology (ACR) Appropriateness Criteria, a Radiography chest is Usually appropriate as the initial imaging study.

Who Fits This Clinical Scenario for Sepsis Imaging?

This guidance applies to a specific and challenging patient population: those with suspected or confirmed sepsis who lack clear, organ-specific symptoms to guide the diagnostic workup. The key feature is the absence of a clinical pointer toward the source of infection.

Inclusion criteria for this workflow include patients who:

  • Meet clinical criteria for sepsis or septic shock (e.g., based on SOFA or qSOFA scores).
  • Are unable to provide a reliable history due to altered mental status, delirium, dementia, intoxication, or intubation and mechanical ventilation.
  • Have a non-focal physical examination that does not suggest a specific site of infection.

It is crucial to distinguish this presentation from similar, but distinct, clinical scenarios. This guidance does not apply if the patient has clear localizing signs.

Exclusion criteria (patients who fit a different ACR variant) include:

  • Patients with pulmonary symptoms: If the patient has a prominent cough, dyspnea, or chest pain, they fit the specific scenario for sepsis with suspected pulmonary origin.
  • Patients with abdominal pain: If the patient has acute abdominal pain, tenderness, or guarding, they should be evaluated under the sepsis with an acute abdomen pathway.
  • Patients with known urinary symptoms: If dysuria, frequency, or flank pain is present, the workup should be tailored to a suspected urinary source.

This workflow is designed for the truly undifferentiated septic patient, where imaging is used as a screening tool to find a common, occult source.

What Diagnoses Are You Working Up in This Scenario?

When a patient presents with sepsis of unknown origin, the initial imaging strategy is designed to identify the most common and life-threatening sources that can be clinically silent, particularly in elderly or debilitated individuals. The differential diagnosis is broad, but the workup prioritizes high-probability etiologies.

Pneumonia is the most frequent cause of community-acquired sepsis and a leading cause of sepsis overall. In elderly, immunocompromised, or non-ambulatory patients, the classic symptoms of cough and sputum production may be absent. Aspiration events can be silent, and the only initial signs may be fever and altered mental status. A chest radiograph is the primary modality for detecting the parenchymal consolidation characteristic of pneumonia.

An intra-abdominal or pelvic source is another common culprit. Conditions like cholecystitis, cholangitis, diverticular abscess, appendicitis, or pyelonephritis can present without focal pain, especially in patients with diabetic neuropathy or those on corticosteroids. The initial physical exam can be misleadingly benign. While a chest radiograph will not identify these, its role is to first rule out the more common pulmonary source.

A urinary tract infection (UTI), particularly complicated UTI or pyelonephritis, is a very common source of sepsis in older adults. While a urinalysis is the key initial diagnostic test, a silent pyelonephritis or an obstructing kidney stone leading to pyonephrosis can be the underlying cause.

Less common but critical considerations include occult soft tissue infections (e.g., deep abscess, necrotizing fasciitis), musculoskeletal infections (septic arthritis, osteomyelitis), or central line-associated bloodstream infections. The initial imaging choice is a pragmatic one, targeting the highest-yield location first.

Why Is a Chest Radiograph the Recommended First Study for This Presentation?

In the undifferentiated septic patient, the ACR designates a chest radiograph as Usually appropriate because it offers a rapid, low-risk, and high-yield method to investigate the single most common cause of sepsis: pneumonia. The rationale is rooted in diagnostic efficiency and patient safety.

A portable, anteroposterior (AP) chest radiograph can be performed quickly at the bedside without moving an unstable patient. It provides crucial information about the presence of a pulmonary infiltrate, consolidation, pleural effusion, or signs of acute respiratory distress syndrome (ARDS). A positive finding can immediately establish a source, guide empiric antibiotic selection, and potentially avert the need for more advanced, higher-risk imaging. The radiation exposure is minimal (adult relative radiation level ☢ <0.1 mSv), a key consideration in any patient, but especially one who may require serial imaging.

**Why are other, more comprehensive studies rated lower for the initial step?**

  • CT chest abdomen pelvis with IV contrast: This “pan-scan” is rated May be appropriate. While it provides a comprehensive evaluation of the three major body cavities, it is not the ideal first-line test. It exposes the patient to significantly higher radiation (RRL ☢☢☢☢ 10-30 mSv) and requires IV contrast. Septic patients are often hemodynamically unstable and at high risk for acute kidney injury (AKI), making contrast administration a significant concern. The logistical burden of transporting an unstable patient to the CT scanner is also a factor. This study is best reserved as a second-line investigation if the initial workup is unrevealing.
  • Radiography abdomen: This study is rated Usually not appropriate. A plain film of the abdomen has very poor sensitivity for the most common intra-abdominal sources of sepsis, such as abscess, cholecystitis, or pyelonephritis. Its utility is largely limited to detecting free intraperitoneal air from a perforated viscus or findings of a high-grade bowel obstruction, which are less common presentations of occult sepsis compared to pneumonia.

By starting with a chest radiograph, the clinical team follows a logical, evidence-based pathway that prioritizes the most probable diagnosis with the least invasive and safest test.

What’s Next After Radiography chest? Downstream Workflow

The result of the initial chest radiograph is a critical branch point in the diagnostic algorithm for sepsis of unknown origin. The next step depends entirely on its findings.

  • If the chest radiograph is POSITIVE: If the study reveals a clear consolidation, large pleural effusion, or other findings consistent with pneumonia, a pulmonary source is presumed. The immediate next steps are clinical: tailor antibiotic therapy to cover likely respiratory pathogens and obtain sputum cultures if possible. Further extensive imaging is often unnecessary unless the patient fails to improve on appropriate therapy, which might suggest a complication like an empyema.
  • If the chest radiograph is NEGATIVE or EQUIVOCAL: A normal chest radiograph makes a pulmonary source less likely (though it doesn’t completely exclude it, especially in early or atypical pneumonia). The workup must then proceed to evaluate other potential sources, primarily the abdomen and pelvis. This is the point where a more advanced study becomes appropriate. The next logical step, as outlined in the corresponding ACR variant, is often a CT of the abdomen and pelvis with IV contrast. This study is excellent for identifying abscesses, inflammatory processes, or urinary tract abnormalities.
  • If the chest radiograph is INDETERMINATE: Findings like atelectasis, small effusions, or subtle interstitial changes can be nonspecific in a critically ill patient. In this case, clinical correlation is key. If pulmonary symptoms are absent and other clues (e.g., abnormal liver function tests, pyuria) point toward an abdominal source, it is reasonable to proceed to abdominal imaging. If suspicion for a pulmonary source remains high despite the nonspecific radiograph, a CT chest with IV contrast may be warranted to better characterize the lung parenchyma and identify subtle pneumonia or pulmonary emboli.

The initial chest radiograph is not the end of the workup; it is the efficient first filter that directs the subsequent, more targeted investigation.

Pitfalls to Avoid (and When to Get Help)

When managing sepsis without a clear source, several common pitfalls can delay diagnosis and treatment.

  • Over-reliance on a “normal” exam: In elderly, diabetic, or immunosuppressed patients, the physical exam can be deceptively benign. Do not let a non-tender abdomen dissuade you from considering an intra-abdominal source if the initial chest x-ray is negative.
  • Delaying the initial image: In a septic patient, time is critical. The initial chest radiograph should be obtained rapidly, often with a portable unit in the resuscitation bay, to avoid delays in source identification.
  • Forgetting non-infectious mimics: Conditions like pulmonary embolism, pancreatitis, or adrenal crisis can mimic sepsis. If the infectious workup is negative, reconsider the differential diagnosis for shock.
  • Ignoring the urinary source: Always obtain a urinalysis and culture early in the workup. A complicated UTI or pyelonephritis is a common and treatable source of sepsis that may not require advanced imaging if it responds to antibiotics.

If the patient remains unstable and the initial chest radiograph and subsequent abdominal CT are unrevealing, it is time to escalate. This includes broadening the differential, consulting infectious disease or critical care specialists, and considering less common sources like endocarditis (requiring echocardiography) or central nervous system infection.

Related ACR Topics and Tools

For further reading and to explore adjacent clinical scenarios, the following resources are available. For breadth across all scenarios in Sepsis, see our parent guide: Sepsis: ACR Appropriateness Decoded.

Frequently Asked Questions

Why not just order a CT ‘pan-scan’ on every septic patient without a source?

While a CT ‘pan-scan’ (chest, abdomen, and pelvis) is comprehensive, it’s rated ‘May be appropriate’ rather than ‘Usually appropriate’ as the first step due to significant radiation exposure and the risks of IV contrast, particularly acute kidney injury in unstable patients. The ACR recommends a stepwise approach, starting with a low-risk, high-yield chest radiograph to rule in or out the most common source (pneumonia) before escalating to higher-risk imaging.

What if the patient is too unstable to go to the CT scanner but the chest x-ray is negative?

If the patient is too hemodynamically unstable for transport to CT, a bedside ultrasound of the abdomen can be a valuable next step. It is rated ‘May be appropriate’ and can rapidly assess for free fluid, hydronephrosis, gallbladder wall thickening, or a pericardial effusion. While less sensitive than CT for many conditions, it provides critical information without risk or transport.

Does a normal chest radiograph completely rule out pneumonia?

No. A chest radiograph can be negative in the early stages of pneumonia, especially in dehydrated or severely neutropenic patients. If clinical suspicion for pneumonia remains very high despite a negative radiograph, a non-contrast or contrast-enhanced chest CT may be necessary for definitive evaluation. This is covered in a separate ACR scenario for sepsis with pulmonary symptoms and a negative initial radiograph.

Is there a role for MRI in the initial workup of sepsis without a source?

No, MRI is rated ‘Usually not appropriate’ for the initial, undifferentiated workup. MRI is a time-consuming study that requires a stable, cooperative patient and is generally not suited for a rapid survey for an unknown septic source. It is a problem-solving tool used for specific indications later in the workup, such as suspected spinal epidural abscess or complex soft tissue infection, once the investigation has been focused.

Should I order a non-contrast CT instead of a contrast-enhanced CT to protect the kidneys?

For this scenario, a CT of the abdomen and pelvis without IV contrast is rated ‘Usually not appropriate’. While it avoids contrast, its diagnostic utility for identifying an infectious source is severely limited. It cannot adequately evaluate for abscesses, vascular pathology, or solid organ inflammation. If a CT is deemed necessary after a negative chest x-ray, the diagnostic benefit of a contrast-enhanced study generally outweighs the risk, though the decision must be individualized based on the patient’s renal function and clinical status.

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