A blood based solute monitoring system for measuring at least one blood solute species that has a first recirculation flow path in communication with a dialyzer. The first recirculation flow path is configured to allow a fluid to recirculate through a dialyzer such that the concentration of at least one solute species in the fluid becomes equilibrated to the solute species concentration of the blood compartment of the dialyzer. The blood solute monitoring system has at least one sensor to measure a fluid characteristic.