#68 Novel clinical application of urinary angiotensin-converting enzyme assay in renal sarcoidosis: a retrospective observational study

Abstract

Abstract Background and Aims Renal manifestations of sarcoidosis are observed in approximately 1–5% and characterized mainly by granulomatous interstitial nephritis, which could lead to kidney failure. Angiotensin-converting enzyme (ACE) reflects the presence of granuloma; hence, serum ACE and tubular injury markers are measured in renal sarcoidosis (RS); however, they either have low sensitivity or low specificity. Although its practicality has not been established, the use of ACE levels in cerebrospinal fluid has been reported for neuro-sarcoidosis. Therefore, we hypothesized that urinary ACE could reflect granuloma presence in the kidneys and could be a disease-specific marker for RS. Method This was a single-center, retrospective observational study. We evaluated clinical characteristics and kidney biopsy findings from electronic medical record surveys and kidney biopsy specimens. The control groups included sarcoidosis without renal involvement (SAR-control) and tubulointerstitial nephritis without a sarcoidosis etiology (TIN-control). Serum and urinary ACE levels were measured, and urinary fractional excretion of ACE (FEACE) was investigated. Serum ACE assay and urinary ACE levels were measured using the colorimetric method with p-hydroxybenzoyl-glycyl-L-histidyl-L-leucine. A total of six patients (three with RS; one with sarcoidosis as controls; and two with TIN controls) with undetectable urinary ACE levels were excluded from the urinary ACE and FEACE analyses. Tubulointerstitial lesions were visually assessed for essentially normal (%), inflammatory cell infiltrates (%), tubular atrophy (%), and interstitial fibrosis (%) by several board-certified nephrologists, and analyzed the correlation of these lesions with each marker. Results This study included 18 patients with RS, 18 as SAR-control, and 10 as TIN-control. Serum ACE, urinary ACE, and FEACE levels in the RS group were significantly higher than those in the control groups. Receiver operating characteristic analysis identified FEACE and serum ACE levels as useful biomarkers for diagnosing RS among patients with both controls, respectively. In the RS group, FEACE was positively correlated with the degree of tubulointerstitial injury (r = 0.69, P = 0.0045), and the cutoff value of FEACE for diffuse tubulointerstitial injury (50.0% or more) was 0.39%, with a sensitivity and specificity of 100.0%. Furthermore, obvious positive correlations were observed among FEACE, inflammatory cell infiltrates (r = 0.53, P = 0.044), and interstitial fibrosis (r = 0.56, P = 0.029) in the RS group but not in the TIN-control. Conclusion Combination with serum and urinary ACE could help diagnose and assess disease severity among patients with RS.