Provided is a blood diagnosis method and a dialysis machine, using a diagnostic marker which is versatile and which can contribute to the improvements in dialysis treatment and the evaluation of clinical effects, the method including a step for collecting a blood sample from a dialysis patient before and after dialysis; and a step for making a diagnosis regarding the collected blood sample based on a biomarker, wherein the biomarker is identified in advance based on the correlation between the urea clear space (CS) or the cellular membrane clearance (Kc) and profiles of mRNA or proteins.