Jalal K, et al. - Among Chronic Kidney disease (CKD) patients from a large insurer database, researchers assessed the diagnostic accuracy of CKD-staging International Classification of Diseases (ICD) codes for detecting subjects rapidly progressing towards end-stage renal disease. Of 216,529 patients, serial observations including outpatient serum creatinine measurements obtained from 2007 through 2014 were analyzed. They contrasted CKD progression, using a serum creatinine based longitudinal mixed-model, with that reported by CKD-staging ICD codes. Compared with gold standard estimated glomerular filtration rate measures, poor capacity of ICD-codes to detect rapidly progressing CKD patients was demonstrated as a novel finding in this study. In CKD diagnosis, the limitations of coding were also shown. ICD codes were identified to have limitations in addressing the diagnosis of disease severity or disease progression for clinical or epidemiological purposes.