The present invention pertains to a method for monitoring a treatment of a patient, preferably for monitoring hemodialysis, hemodiafiltration and/or peritoneal dialysis, the method comprising the steps of irradiating a sample of a dialysis liquid used in the treatment with irradiation light of at least a first irradiation wavelength, detecting light emitted by the irradiated sample in at least a first detection wavelength, the detection wavelength being different from the first irradiation wavelength, and determining the presence and/or concentration of at least one analyte in the sample on the basis of the detected light.