Hemodialysis patients are susceptible to life-threatening arrhythmias whose incidence is markedly higher during the long interdialytic interval due to electrolyte Fluctuations. Noninvasive monitoring of electrolyte fluctuations, particularly those of potassium, would enable restoring electrolyte balance before the onset of arrhythmias. This study investigates the feasibility of continuous long-term monitoring of potassium fluctuations using a single-lead electrocardiogram. We evaluate patient-specific T-wave morphology changes in the electrocardiogram using two descriptors: 1) a model-based descriptor, theta(delta) developed to account for overall morphology changes, and 2) the currently available descriptor, TSA, sensitive to potassium levels in single-lead electrocardiograms. Electrocardiograms of 15 hemodialysis patients with pre-existent cardiac diseases were acquired continuously over the long interdialytic interval along with blood samples at predetermined time instants. Results reveal that theta(delta) and TSA respond concordantly with potassium levels, and reacts to potassium lowering medication. The overlapping index of the daily distributions of theta(delta) and TSA are moderately correlated with changes in potassium levels (r D 0 :56 and r D 0 :57, respectively). theta(delta) exhibits circadian variation, peaking amidst morning and decreasing until evening. theta(delta) appears to be less affected by motion-induced noise, which is preferable for ambulatory monitoring. Although long-term monitoring of potassium fluctuations is feasible even in complicated hemodialysis patients, the presence of concomitant electrolyte (calcium and bicarbonate) imbalances should be accounted for since it can hamper a reliable estimation. Considering that intradialytic T-wave morphologies may differ from the ones manifested between hemodialysis sessions, future studies should also strive to collect blood samples outside of hemodialysis to improve electrolyte estimation methods.