An extracorporeal blood treatment system, comprising: a first holder, the first holder holding when the system is in use a blood treatment device having a blood chamber, a fluid chamber and a semipermeable membrane that separates the chambers (15, 16) from each other; a second holder, the second holder holding when the system is in use an extracorporeal blood circuit coupled to the blood treatment device; and a control unit configured to operate at least one pump to cause blood to flow through the blood treatment device and the extracorporeal blood circuit, wherein the control unit is further configured to execute a procedure comprising: prior to commencing an extracorporeal blood treatment, reading from a storage device (4a, 5a) stored values of a patient-specific prescription parameter, the patient-specific prescription parameter being an end-of-treatment parameter in the group including a water-refilling index, a final relative blood volume (ΔBV), a final blood volume (BV%), and a variation of weight loss (ΔWL%), wherein the stored values relate to a sequence of previous extracorporeal blood treatments; processing the stored values of the prescription parameter read from the storage device (4a, 5a) according to a predetermined alogrithm to determine a current value of the patient-specific prescription parameter, wherein the current value is then available for the subsequent extracorporeal blood treatment; using a default value as the current value if less than a threshold number of stored values is read; deeming valid the current value if within a predetermined range of acceptability, if not, discarding the current value; and once the current value is deemed valid, suggesting the current value to the user and requiring him/her to either accept or to discard the suggested parameter, or using the current value as a set value for the patient-specific prescription parameter. a first holder, the first holder holding when the system is in use a blood treatment device having a blood chamber, a fluid chamber and a semipermeable membrane that separates the chambers (15, 16) from each other; a second holder, the second holder holding when the system is in use an extracorporeal blood circuit coupled to the blood treatment device; and a control unit configured to operate at least one pump to cause blood to flow through the blood treatment device and the extracorporeal blood circuit, wherein the control unit is further configured to execute a procedure comprising: prior to commencing an extracorporeal blood treatment, reading from a storage device (4a, 5a) stored values of a patient-specific prescription parameter, the patient-specific prescription parameter being an end-of-treatment parameter in the group including a water-refilling index, a final relative blood volume (ΔBV), a final blood volume (BV%), and a variation of weight loss (ΔWL%), wherein the stored values relate to a sequence of previous extracorporeal blood treatments; processing the stored values of the prescription parameter read from the storage device (4a, 5a) according to a predetermined alogrithm to determine a current value of the patient-specific prescription parameter, wherein the current value is then available for the subsequent extracorporeal blood treatment; using a default value as the current value if less than a threshold number of stored values is read; deeming valid the current value if within a predetermined range of acceptability, if not, discarding the current value; and once the current value is deemed valid, suggesting the current value to the user and requiring him/her to either accept or to discard the suggested parameter, or using the current value as a set value for the patient-specific prescription parameter. prior to commencing an extracorporeal blood treatment, reading from a storage device (4a, 5a) stored values of a patient-specific prescription parameter, the patient-specific prescription parameter being an end-of-treatment parameter in the group including a water-refilling index, a final relative blood volume (ΔBV), a final blood volume (BV%), and a variation of weight loss (ΔWL%), wherein the stored values relate to a sequence of previous extracorporeal blood treatments; processing the stored values of the prescription parameter read from the storage device (4a, 5a) according to a predetermined alogrithm to determine a current value of the patient-specific prescription parameter, wherein the current value is then available for the subsequent extracorporeal blood treatment; using a default value as the current value if less than a threshold number of stored values is read; deeming valid the current value if within a predetermined range of acceptability, if not, discarding the current value; and once the current value is deemed valid, suggesting the current value to the user and requiring him/her to either accept or to discard the suggested parameter, or using the current value as a set value for the patient-specific prescription parameter.