What urinalysis result is most indicative of acute pyelonephritis?

In the context of acute pyelonephritis, the presence of white cell casts in urinalysis is particularly significant. Acute pyelonephritis is an infection of the kidney that often stems from ascending urinary tract infections. As the infection progresses, inflammatory cells, particularly neutrophils, infiltrate the renal interstitium and the tubules.

When these neutrophils accumulate within the renal tubules, they can become organized into casts that are then shed into the urine, resulting in white cell casts being detected on urinalysis. This finding indicates a renal process involving inflammation and infection, which is characteristic of acute pyelonephritis.

Other potential findings in urinalysis might include bacteria, pus, and a high number of leukocytes, but the specific association of white cell casts aligns strongly with the diagnosis of acute pyelonephritis. The presence of these casts underscores the role of the kidney as the source of infection and inflammation rather than other causes of symptoms.