Association Between the Earliest CALLY Index at Diagnosis and Progression to End-Stage Kidney Disease in Patients with Microscopic Polyangiitis and Granulomatosis with Polyangiitis.

Background and Objectives: This study aimed to determine whether the earliest C-reactive protein (CRP)-albumin-lymphocyte (CALLY) index at diagnosis was associated with progression to end-stage kidney disease (ESKD) during follow-up in patients with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA). Materials and Methods: This study included 247 patients with MPA and GPA. The CALLY index was calculated as follows: serum albumin (g/L) × lymphocyte count (/mm3)/CRP (mg/L)/10,000. The earliest CALLY index was defined as the value calculated at diagnosis. ESKD, which occurred after diagnosis, was defined as a poor outcome in this study. Results: The median age of the 247 patients was 62.0 years and 64.4% were women. Among the 247 patients, 50 (20.2%) progressed to ESKD. The earliest CALLY index at diagnosis was significantly lower in patients with ESKD than those without ESKD (0.15 vs. 0.55). Receiver operating characteristic curve analysis showed that the earliest CALLY index had modest discriminatory performance for progression to ESKD, with an area under the curve of 0.663 and a cut-off value of 0.26. Patients with an earliest CALLY index ≤ 0.26 at diagnosis exhibited a significantly higher risk for progression to ESKD (relative risk 3.174) and a significantly reduced cumulative ESKD-free survival rate compared to those with an earliest CALLY index > 0.26 at diagnosis. Conclusions: This study has exploratory implications, as it is the first to report that the earliest CALLY index was associated with ESKD occurrence during follow-up in patients with MPA and GPA, despite its limited value as an independent predictor of ESKD.