In a patient with persistent fever after 72 hours of appropriate antibiotics, what imaging should be performed if the serum creatinine is 1.5 mg/dL?

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CT Abdomen and Pelvis Without IV Contrast

In a patient with persistent fever after 72 hours of appropriate antibiotics and a serum creatinine of 1.5 mg/dL, perform CT abdomen and pelvis WITHOUT IV contrast to identify the source of infection. 1

Rationale for Non-Contrast CT

A creatinine of 1.5 mg/dL represents mild renal impairment and raises concern about contrast-induced nephropathy. The 2024 ACR Appropriateness Criteria specifically addresses this scenario, noting that confidence in identifying septic foci was not significantly different between CT scans with or without IV contrast (P = .432) 1. This is critical evidence that you can safely proceed with non-contrast imaging without sacrificing diagnostic accuracy.

Diagnostic Yield

Non-contrast CT still provides excellent diagnostic performance in this clinical context:

  • Detection rate of septic foci: 76.5% in patients with suspected sepsis 1
  • Positive predictive value: 81.82% for identifying infection sources 1
  • Change in management: 45% of cases, including surgical intervention and drainage procedures 1

The abdomen and pelvis are the second and third most common sites for septic foci (22.0% and 20.5% respectively), making this imaging essential 1.

When Non-Contrast CT is Particularly Useful

The ACR guidelines explicitly state that non-contrast CT is especially valuable for urosepsis from suspected obstructing renal calculi or ureteral calculi 1. Given the persistent fever despite antibiotics, urinary obstruction should be high on your differential.

Alternative Consideration: Ultrasound First

If urosepsis is strongly suspected based on clinical parameters (history of urolithiasis, urine pH ≥7.0, or this degree of renal insufficiency), you could start with renal ultrasound 2. However, ultrasound has limitations—it missed multiple perirenal abscesses and gas-forming perinephric abscesses that were detected on CT 1.

Common Pitfall to Avoid

Do not order CT with IV contrast reflexively. While contrast-enhanced CT is the gold standard in patients with normal renal function, the evidence shows non-contrast CT maintains diagnostic confidence in identifying infection sources 1. The risk of worsening renal function with contrast outweighs the marginal benefit in diagnostic accuracy at this creatinine level.

If Source Remains Unidentified

Should the non-contrast CT be unrevealing and fever persists, the 2023 ICU fever guidelines recommend considering FDG-PET/CT if transport risk is acceptable 3, though this is typically reserved for more refractory cases after initial cross-sectional imaging.

References

1
Guideline

acr appropriateness criteria® sepsis.

Journal of the American College of Radiology, 2024

2
Research

Predicting the need for radiologic imaging in adults with febrile urinary tract infection.

Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 2010

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.