Development and internal validation of an interpretable machine-learning model for identifying comorbid atrial fibrillation in patients with diabetic kidney disease.

Background: Patients with diabetic kidney disease (DKD) are at increased risk of atrial fibrillation (AF), yet tools to support identification of comorbid AF in this high-burden population remain limited. We aimed to develop and internally validate an interpretable machine-learning (ML) model for identifying concomitant AF in patients with DKD using routinely collected clinical data. Methods: In this retrospective two-center cohort study (January 2021 to October 2025), 787 unique records of patients with DKD were randomly divided into training (70%) and test (30%) sets. AF status was defined as documented atrial fibrillation coexisting with DKD and was ascertained using electrocardiograms, Holter monitoring when available, and ICD-10 diagnostic codes with physician adjudication. Candidate predictors were routine clinical, laboratory, and echocardiographic variables. Least absolute shrinkage and selection operator (LASSO) regression was used for feature selection in the training set. Seven supervised models were trained; performance was assessed by area under the receiver-operating characteristic curve (AUC), calibration, and decision-curve analysis. SHAP quantified feature contributions. Results: LASSO retained 14 features, including 24-hour urine total protein (24UTP), serum creatinine (SCr), age, and atrial dimensions. In the test set, the k-nearest neighbors (KNN) model achieved an AUC of 0.927, with an accuracy of 0.886, sensitivity of 0.920, and specificity of 0.856. Calibration was satisfactory, and decision-curve analysis showed net benefit across commonly used thresholds. Five-fold cross-validation yielded mean AUC 0.90 ± 0.02. SHAP analysis identified proteinuria burden, renal dysfunction, age, and atrial size as major contributors to model output. The final model was translated into a preliminary web-based calculator based on routinely available inputs. Conclusions: An interpretable ML model incorporating routinely collected clinical and echocardiographic variables showed stable internal performance for identifying comorbid atrial fibrillation in patients with DKD. Because the model is intended to identify concomitant AF status rather than predict incident AF and has undergone internal validation only, further external and prospective validation is required before broader clinical application.