Case Presentation: A 70-year-old man with history of diffuse large B-cell lymphoma (status-post 2 cycles of CHOP chemotherapy), COPD, stage 3 chronic kidney disease, and diabetes mellitus presented with generalized weakness and diarrhea. His symptoms began three days prior with head pain, chills, and weakness. He then developed increasing diarrhea from his baseline of one loose stool per day since starting chemotherapy. He had mild generalized abdominal pain, and worsening symptoms led to several days of decreased oral intake, prompting his presentation to the emergency room. On examination, the patient was tachycardic (120 bpm), afebrile (98.7°F), normotensive (114/71 mm Hg) with oxygen saturation 99% on 3L oxygen. His abdomen was soft, non-tender, and non-distended. Laboratory studies revealed leukocytosis (11,000 per mm3), elevated blood urea nitrogen (34 mg/dl), and acute kidney injury (creatinine 2.73 from baseline of 1.8 mg/dl). Urinalysis showed negative nitrites, large leukocytes, small blood, pH 6.0, and 1+ bacteria/hpf. He was empirically started on vancomycin and cefepime. The following morning, his urine culture and 1 of 2 blood cultures returned positive for Proteus mirabilis. After further consideration of the patient’s vague abdominal pain and his immunocompromised state, the clinical team obtained an abdominal CT to evaluate for potential occult nephrolithiasis. Imaging revealed “obstructing right nephrolithiasis with mild to moderate right hydronephrosis and additional bilateral nephrolithiasis.” The patient went urgently to the OR for cystoscopy with ureteral stent placement. Intraoperatively, there was significant purulent drainage after kidney decompression. Post-operatively, the patient reported a remote history of nephrolithiasis and clarified that his abdominal pain radiated to his back, suggesting his initial symptoms were related to renal colic from an obstructed renal calculus and ensuing infection.

Discussion: Patients with urinary tract infection (UTI) and concomitant obstruction require urgent intervention to avoid permanent kidney damage, sepsis, or death. In patients with renal colic and signs of infection such as fever or leukocytosis, providers should not hesitate to obtain abdominal imaging. Proteus mirabilis bacteremia especially raises suspicion for obstruction, as this urease-producing bacteria may develop large struvite stones that can form staghorn calculi. These stones remain infected, leading to bloodstream translocation and sepsis. Mortality rates from bacteremia originating from a UTI near 60%. Despite the potential for rapid decompensation, diagnosis can be challenging. Patients with struvite stones often present with vague symptoms such as mild flank or abdominal pain. Furthermore, immunocompromised patients are at higher risk of UTI and may also not have classic symptoms. Additionally, in the context of renal colic and possible infection, clinicians should not anchor on a negative urinalysis. Although a positive nitrite test is specific for UTI and associated with urea-splitting organisms, the test has poor sensitivity, with only 25% of patients with UTI having a positive nitrite test.

Conclusions: Hospitalists should recognize the association of Proteus mirabilis UTI with staghorn calculi and consider obstructive uropathy, especially in elderly and immunocompromised patients, as a potentially life-threatening diagnosis. Even in patients with mild symptoms, clinicians should have a low threshold to obtain dedicated imaging.