Various embodiment disclosed herein include a method for monitoring serum potassium in a patient. The method can include gathering cardiac electrogram data from the patient using two or more electrodes, separating the cardiac electrogram data into discrete subunits including a T-wave, aligning T-waves to create aligned discrete subunits, averaging the aligned discrete subunits to generate an average T-wave for the cardiac electrogram data, and determining a serum potassium value using the average T-wave for the cardiac electrogram data and a predetermined model relating T-wave values with serum potassium magnitudes.
