Evaluation of Cyst Fluid Appearance and Biochemical Profile in Patients with ADPKD: A Novel Diagnostic Approach for Infected Cysts

Background: Cyst infection is a serious complication in patients with autosomal dominant polycystic kidney disease (ADPKD). Although cyst fluid culture is considered the gold standard for diagnosis, its sensitivity is limited. Moreover, no reliable method currently exists to confirm whether a drained cyst was truly infected. Methods: We conducted a retrospective analysis of 300 ADPKD patients who underwent cyst drainage at our institution between November 2020 and December 2023. A total of 575 cysts (449 hepatic and 126 renal) were evaluated. Clinical data, laboratory parameters, imaging findings, and cyst fluid appearance and biochemical profiles were compared between infected and non-infected cysts. Based on these variables, a diagnostic model for cyst infection was developed and validated. Results: Cyst fluid from infected cysts showed significant inflammatory changes, including turbidity, elevated lactate dehydrogenase (LDH) levels, and increased white blood cell counts. A diagnostic model incorporating cyst fluid turbidity, LDH, and serum C-reactive protein (CRP) levels demonstrated excellent performance, with both sensitivity and specificity exceeding 90%, and an area under the receiver operating characteristic curve (AUC) greater than 0.98. Conclusion: Post-drainage analysis of cyst fluid appearance and biochemical parameters can accurately identify infected cysts in ADPKD patients, providing a novel and reliable diagnostic approach.