Infected Stones: Interpreting Borderline UAs and Admission Decisions

Brit Long, MD and Matthew DeLaney, MD, FACEP, FAAEM

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The summary below is from an episode of ERcast: Clinical Perspectives

Infected urolithiasis is a sepsis-prone obstructive urinary emergency, not a routine kidney stone visit. Fever is the strongest bedside predictor, urinalysis is often more useful than bloodwork for early suspicion, and obstruction is what turns infection into a mortality problem.

Diagnosing Infected Urolithiasis

Fever as key predictor: Fever is the strongest clinical clue to an infected stone, and 20-50% of these patients can progress to sepsis or septic shock if obstruction and infection travel together.
Borderline UA interpretation: Pyuria above 5 WBCs/hpf and positive leukocyte esterase support infection, but positive nitrites should be treated as infection until proven otherwise. We get into the gray-zone UA nuance in the episode.
Symptoms that actually matter: Reported fever, dysuria, chills, frequency, and malodorous urine increase concern for infected urolithiasis, while hematuria, nausea, and vomiting do not reliably separate it from an uncomplicated stone.
Contamination and false reassurance: Squamous cells point toward a contaminated specimen worth repeating, and a normal CBC or creatinine does not reliably exclude infection even when the urinalysis is equivocal.
Working ED definition: There is no universal ED definition for an infected kidney stone; the practical bedside diagnosis rests on a stone plus convincing urinalysis and clinical infection features while culture is pending.

Imaging, Treatment, and Disposition

CT imaging advantage: CT is the preferred imaging test when infected urolithiasis is suspected, and IV contrast can better show alternate diagnoses, abscess, and the severity of obstruction for procedural planning.
Ultrasound septic screen: Ultrasound is useful when a UTI patient looks septic because hydronephrosis supports obstruction, and pyonephrosis is a particularly dangerous finding with a strong diagnostic signal.
Antibiotic first-line choice: Management centers on resuscitation, antibiotics, and urgent urology input, with ceftriaxone as an excellent initial agent before broader gram-negative coverage for sicker or higher-risk patients.
Urgent decompression imperative: Infected stones with obstruction need prompt collecting-system drainage because delayed decompression drives AKI and mortality; survival improves when source control happens early.
Who can go home: Discharge is limited to patients with smaller non-obstructing stones who are well-appearing, afebrile, able to take oral antibiotics, and able to secure close urology follow-up. We walk through the admission-versus-discharge judgment in the chapter.

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References:

Yoo MJ, Pelletier J, Koyfman A, Long B. High risk and low prevalence diseases: Infected urolithiasis. Am J Emerg Med. 2024;75:137-142. PMID: 37950981
Reyner K, Heffner AC, Karvetski CH. Urinary obstruction is an important complicating factor in patients with septic shock due to urinary infection. Am J Emerg Med. 2016;34(4):694-696. PMID: 26905806

Faculty

Brit Long, MD
Dr. Brit Long is a Professor of Emergency Medicine at the University of Virginia and an emergency medicine physician with experience in both a community ED and at a military academic center ED. He is the Clinical Editor-in-Chief of emDOCs.His professional interests include medical education, evidence-based medicine, and the FOAMed movement. Outside of work, he enjoys spending time with his wife and two daughters
Matthew DeLaney, MD, FACEP, FAAEM
Dr. Matthew DeLaney is an emergency medicine physician and educator based in Birmingham, Alabama. A native of Mobile, he earned his medical degree from the University of South Alabama and completed his emergency medicine residency at Maine Medical Center.Dr. DeLaney has experience in both community and academic emergency medicine and is known for his commitment to teaching and medical education. He lives in Birmingham with his wife, Erin, who is also a physician, and their two daughters.