Inclusion Criteria:

(Arm 2A - Outpatient Diagnostic Accuracy)

• Age 22 years or older
• CKD stages III-IV managed at Central Jersey Kidney Care outpatient clinic
• Scheduled outpatient serum potassium laboratory test
• On RAASi therapy or documented hyperkalemia (K+ ≥ 5.5 mmol/L) within the past 12 months
• Able to provide written informed consent

(Arm 2B - Remote Patient Monitoring)

• Completion of Arm 2A visit
• Owns an iPhone compatible with the study application

Exclusion Criteria (Both arms):

• Age 21 years or younger
• Pacemaker or implantable cardioverter defibrillator
• Pre existing Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB), Intraventricular Conduction Delay (IVCD), or clinically significant hypocalcemia
• Potassium lowering treatment administered before Lead I ECG acquisition
• Trauma, acute events, or active interventions altering potassium homeostasis
• Physical limitation precluding ECG acquisition