ACUTE PYELONEPHRITIS: CLINICAL FEATURES, DIAGNOSIS, AND PRINCIPLES OF INITIAL MANAGEMENT

Acute pyelonephritis (AP) is an infectious-inflammatory process involving the renal pelvicalyceal system and renal parenchyma and is considered one of the most important clinical manifestations of upper urinary tract infection (upper UTI) in practice. AP is often associated with ascending bacterial invasion from the lower urinary tract (cystitis); etiologically, Escherichia coli holds a leading position and has been identified as the principal pathogen in numerous population-based observations. The clinical relevance of the disease is determined by three factors: (1) a high incidence and increased risk of severe course among women, pregnant individuals, older adults, people living with diabetes, and patients with urologic obstruction; (2) complications such as urosepsis and acute deterioration of renal function; and (3) the need to rationalize empiric antibiotic selection amid the growing burden of antimicrobial resistance. The EAU recommendations specifically emphasize infection control and antimicrobial stewardship (rational use) as key principles in the management of AP. This article presents an evidence-based overview of AP clinical signs, laboratory and imaging diagnostic algorithms, criteria for distinguishing “uncomplicated” versus “complicated” cases, indications for urgent hospitalization, and contemporary principles of initial treatment. Within the framework of NICE NG111 and IDSA/EAU guidelines, the analysis addresses empiric therapy strategies, de-escalation based on culture results, the use of imaging investigations (ultrasound/CT) when indicated, and monitoring of treatment effectiveness.