The invention relates to a calculation and control system for the determination of the state of a vascular access of a patient intended to follow successive sessions of extracorporeal blood treatment by extraction and return of the blood via the vascular access, the system comprising: means for determining the value of at least one hemodynamic extracorporeal parameter of the patient for at least two sessions； means for determining the value of the purification effectiveness of the treatment for at least two sessions； programmed means for determining a risk score relating to the state of the vascular access of the patient as a function of at least two values of the hemodynamic extracorporeal parameter and of at least two determined values of the purification effectiveness.
