Long-term analytical drift of serum creatinine and its association with CKD staging consistency based on eGFR: a retrospective study.

To evaluate whether long-term IQC-derived analytical variability of serum creatinine (SCr), even within allowable limits, is associated with estimated glomerular filtration rate (eGFR)-based chronic kidney disease (CKD) staging consistency and stage reclassification. This single-center retrospective study included 4,215 patients with stable kidney function and 10,481 SCr records from 2022-2024. Daily relative analytical deviation was estimated using a 5-day moving median of IQC results. After analytical-deviation adjustment, eGFR was recalculated using the 2021 CKD-EPI equation and CKD stages were reassigned. Reclassification was defined as stage inconsistency before versus after adjustment. Associated factors were analyzed using multivariable generalized estimating equation logistic regression. All IQC-derived analytical deviations remained within the CLIA 2025 limit (±10%). Positive deviation occurred in 89.2% of records, and 31.6% had an absolute deviation ≥ 5%. Overall, 5.3% (559/10,481) of records were reclassified, with 98.2% shifting from higher-risk to lower-risk CKD stages. Reclassification rates for CKD stages G3a, G3b, and G4 were 12.73%, 19.48%, and 44.44%, respectively. Each 1% increase in analytical-deviation magnitude was associated with higher reclassification risk (aOR = 1.39, 95% CI: 1.34-1.43, p < 0.001), whereas reagent change within 30 days was not significant. Within permissible limits, long-term IQC-derived analytical deviation of SCr assays is significantly associated with CKD stage reclassification, especially near eGFR decision thresholds. Positive IQC-derived analytical deviation was associated with a higher likelihood of apparent CKD stage overestimation. These findings inform quality control and eGFR interpretation, but generalizability requires multicenter prospective validation.