An object of the present invention is to provide an oral preparation that can be used to diagnose the existence or degree of pyridine metabolic capacity disorder, pyrimidine metabolic rate, etc., with high accuracy and with little variation due to individual differences. The oral preparation is prepared using a powder material obtained by mixing and pulverizing (a) an isotope-labeled compound and/or a pyrimidine metabolite compound and (b) a sugar and/or a sugar alcohol.
