A 35-year-old non-pregnant woman presents to the emergency department with complaints of fever, chills, and severe flank pain. Which assessment finding would be most indicative of pyelonephritis in this patient?

When a patient presents with fever, chills, and flank pain, immediately assess for costovertebral angle (CVA) tenderness. To elicit this, place one hand flat over the costovertebral angle and strike it with the ulnar surface of your other fist. Sharp pain on percussion strongly suggests acute pyelonephritis due to stretching of the inflamed renal capsule. This finding, combined with high fever and rigors, distinguishes an upper UTI from a lower UTI, which typically lacks systemic symptoms and flank pain. Early recognition is critical to initiate urine cultures, blood cultures if sepsis is suspected, and empiric antibiotics to prevent progression to urosepsis or renal abscess.