Identifying a cohort of hospitalized chronic kidney disease patients using electronic health records: lessons learnt and implications for future research and clinical practice guidelines.

Background: Safe medication prescribing for hospitalized chronic kidney disease (CKD) patients is challenging. Leveraging electronic health records (EHRs) offers potential for decision support. A first step is to capture the CKD cohort through so called electronic phenotypes (e-phenotypes). However, available e-phenotypes, defined by logical rules applied to EHR data, lack consensus and are often inconsistently aligned with the Kidney Disease - Improving Global Outcomes (KDIGO) guideline for CKD (KDIGO-CKD). Therefore, local analyses and formalization efforts are essential to derive logical rules for CKD cohort selection. Methods: We analyzed routinely collected EHR data from adults hospitalized at Amsterdam University Medical Centre (2018-23). Six logical rules were investigated: four derived from KDIGO-CKD (reduced glomerular filtration rate, albuminuria, kidney replacement therapy, and other markers of kidney damage) and two from published studies (diagnosis codes and medications). Results: The study included 108 854 hospitalized patients. Extensive efforts were needed to formalize the clinical CKD definition from KDIGO-CKD and adapt it to EHR data, including selecting appropriate CKD diagnosis codes, medications, and computable criteria. Pooling six logical rules resulted in identifying 17 805 hospitalized CKD patients (16.4%), showcasing varying CKD patient counts per rule (with proportions ranging from 2.1% to 8.4%). Nonetheless, baseline characteristics across cohorts were comparable. Over one-third of patients identified by decreased eGFR or albuminuria/proteinuria measurements lacked a corresponding diagnosis code. Conclusions: Deriving and formalizing six logical rules required close collaboration between nephrologists, EHR data experts, and medical informaticians. Our study provides groundwork towards a computer-interpretable CKD definition to standardize cohort capture in EHR-based studies.