New insights into acute-on-chronic kidney disease in nephrology patients: the CKD-REIN study

Background Acute-on-chronic kidney disease (ACKD) is poorly understood and often overlooked. We studied its incidence, circumstances, determinants and outcomes in patients with CKD. Methods We used the Kidney Disease: Improving Global Outcomes criteria to identify all-stage acute kidney injury (AKI) events in 3033 nephrology outpatients with CKD Stages 3-5 participating in the CKD-Renal Epidemiology and Information Network cohort study (2013-20), and cause-specific Cox models to estimate hazard ratios [HRs; 95% confidence intervals (CIs)] of AKI-associated risk factors. Results At baseline, 22% of the patients [mean age 67 years, 65% men, mean estimated glomerular filtration rate (eGFR) 32 mL/min/1.73 m(2)] had a history of AKI. Over a 3-year follow-up, 443 had at least one AKI event: 27% were Stage 2 or 3 and 11% required dialysis; 74% involved hospitalization including 47% acquired as hospital inpatients; and a third were not reported in hospital discharge reports. Incidence rates were 10.1 and 4.8/100 person-years in patients with and without an AKI history, respectively. In 2375 patients without this history, male sex, diabetes, cardiovascular disease, cirrhosis, several drugs, low eGFR and serum albumin levels were significantly associated with a higher risk of AKI, as were low birth weight (<2500 g) (adjusted HR 1.98; 95% CI 1.35-2.91) and haemoglobin level (HR 1.21; 1.12-1.32 per 1 g/dL decrease). Within 1 year, only 63% of the patients had recovered their previous kidney function, 13.7% had started kidney replacement therapy and 12.7% had died. Conclusions The study highlights the high rate of hospital-acquired AKI events in patients with CKD, and their underreporting at hospital discharge. It also reveals low birth weight and anaemia as possible new risk factors in CKD patients.