quantification of caffeine (1,3,7 trimethylxanthine) or any metabolite derived from caffeine, including paraxanthine (1,7 dimethylxanthine), theophylline (1,3 dimethylxanthine), and theobromine (3,7 dimethylxanthine) in a sample. The trait is EFO_0007872 (caffeine metabolite measurement).