A method for distinguishing between kidney dysfunctions in a mammal, including pre-renal azotemia, an acute renal injury that may progress to acute renal failure, and chronic kidney disease, using a urinary or circulating NGAL assay result that is compared to a predetermined NGAL cutoff level, and a single serum or plasma creatinine measurement. When the communication service unit 2 receives the service ID and the password from the communication terminals 3A to 3C, the communication service unit 2 collates whether or not the service ID and the password sent from the communication terminals 3A to 3C agree with those sent from the service receiving server 1. The target agents attach the device and are removed from the sample.