Acute obstructive pyelonephritis due to urolithiasis represents a medico-surgical emergency that can lead to life-threatening complications. There are still no established factors that reliably predict progression toward acute pyelonephritis in patients presenting with a simple renal colic.

To investigate clinical and paraclinical factors that are associated with the onset of acute obstructive pyelonephritis.

Patients presenting to the emergency department for renal colic with obstructive urolithiasis on imaging were enrolled in the study. Demographic data, vital signs, medical comorbidities, blood test results, urinalysis, and radiological findings were recorded. Obstructive pyelonephritis was defined by the presence of two or more of the following criteria: fever, flank pain or costovertebral angle tenderness, and a positive urine culture.

Seventeen patients out of 120 presenting with renal colic, were diagnosed with acute obstructive pyelonephritis (14%). Parameters that were associated with the onset of obstructive pyelonephritis were: diabetes (p = 0.03), elevated CRP (p = 0.01), stone size (>5 mm) (p = 0.03), dilatation of renal pelvis (p = 0.01), peri-renal fat stranding (p = 0.02), and positive nitrites on urinalysis (p < 0.01). Hyperleukocytosis, acute kidney injury, multiple stones, pyuria (>10/mm³), hypertension, and were not associated with the onset of obstructive pyelonephritis.

This study showed that known diabetic status, elevated CRP, positive urine nitrites, stone size (>5 mm), pyelic dilatation, and peri-renal fat stranding were associated with the onset of pyelonephritis in patients presenting to the emergency department with obstructive urolithiasis.