A method of predicting serum potassium concentrations in a patient during hemodialysis, the method comprising: measuring serum potassium concentrations ("C") of the patient over a hemodialysis treatment session time and an ultrafiltration rate ("Q UF ") calculated by a difference between pre- and post-dialytic body weight of the patient during an initial hemodialysis treatment session divided by a total treatment time of the treatment session; estimating K M and V PRE for the patient using a non-linear least squares fitting to the equations: C t = C PRE K M + DC D / C PRE K M + K R + D − Q UF 1 − K M + DC D / C PRE K M + K R + D − Q UF × V t V PRE K M + K R + D − Q UF Q UF C T = C PRE − C PRE − C POST e − K M T V PRE − Q UF t tx wherein t is a time during the hemodialysis treatment session, T is a time after an end of the hemodialysis treatment session, t tx is a total duration of the hemodialysis treatment session, C PRE is a pre-dialysis plasma potassium concentration, C POST is a post-dialytic plasma potassium concentration, C D is a dialysate potassium concentration, K M is a potassium mobilization clearance of the patient, K R is a residual renal clearance of potassium, D is a dialyzer potassium dialysance, V PRE is a pre-dialysis distribution volume of potassium of the patient, and V t = V PRE − Q UF × t and predicting C of the patient at any time during any hemodialysis treatment session by using the equations 1-A and 1-B with the estimated K M and V PRE of the patient. measuring serum potassium concentrations ("C") of the patient over a hemodialysis treatment session time and an ultrafiltration rate ("Q UF ") calculated by a difference between pre- and post-dialytic body weight of the patient during an initial hemodialysis treatment session divided by a total treatment time of the treatment session; estimating K M and V PRE for the patient using a non-linear least squares fitting to the equations: C t = C PRE K M + DC D / C PRE K M + K R + D − Q UF 1 − K M + DC D / C PRE K M + K R + D − Q UF × V t V PRE K M + K R + D − Q UF Q UF C T = C PRE − C PRE − C POST e − K M T V PRE − Q UF t tx wherein t is a time during the hemodialysis treatment session, T is a time after an end of the hemodialysis treatment session, t tx is a total duration of the hemodialysis treatment session, C PRE is a pre-dialysis plasma potassium concentration, C POST is a post-dialytic plasma potassium concentration, C D is a dialysate potassium concentration, K M is a potassium mobilization clearance of the patient, K R is a residual renal clearance of potassium, D is a dialyzer potassium dialysance, V PRE is a pre-dialysis distribution volume of potassium of the patient, and V t = V PRE − Q UF × t and wherein t is a time during the hemodialysis treatment session, T is a time after an end of the hemodialysis treatment session, t tx is a total duration of the hemodialysis treatment session, C PRE is a pre-dialysis plasma potassium concentration, C POST is a post-dialytic plasma potassium concentration, C D is a dialysate potassium concentration, K M is a potassium mobilization clearance of the patient, K R is a residual renal clearance of potassium, D is a dialyzer potassium dialysance, V PRE is a pre-dialysis distribution volume of potassium of the patient, and V t = V PRE − Q UF × t and predicting C of the patient at any time during any hemodialysis treatment session by using the equations 1-A and 1-B with the estimated K M and V PRE of the patient.