The invention relates to a dialysis machine with the capability of determining a pre dialysis property in the blood of a dialysis patient which dialysis machine comprises an extracorporeal blood circuit a dialysate circuit a dialyzer and a computing unit wherein at least one sensor for determining a property of the dialysate is arranged in the dialysate circuit. The computing unit is configured in such a way that during an initial phase of the dialysis treatment temporal evaluation ranges are established in which all stability criteria from a predetermined group are satisfied and in such a way that measurement values determined by the at least one sensor are used to determine a pre dialysis property of the patient s blood only within these temporal evaluation ranges.
