Agents to measure the ability to metabolize pyrimidine

Preparation for determining the metabolic ability of pyrimidines in a subject using the expired air, comprising as active principle labeled uracil with 2-C13, 5-fluorouracil labeled 2-C13, uridine marcadacon 2-C13, labeled thymidine 2-C13 or at least one selected from the group consisting entimina compound, 5-bromouracil, 5-fluorotimina, 5-bromothymine, cytosine, uridylic acid, 5-methylcytosine, thymidylic acid, tegafur, carmofur, doxifluridine, dihydrouracil, 5- fluorodihidrouracilo, dihydrothymine, β-ureidopropionic acid, β-ureidopropionic acidofluoro-acid β-ureidoisobutirico, said compound being a labeled isotopoen position 2 of the pyrimidine skeleton carbon