Creatine metabolism disorders include a creatine transporter deficiency, as well as, deficiencies of two enzymes involved in creatine synthesis, arginine–glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT). Laboratory diagnosis of these disorders relies on the determination of creatine and guanidinoacetate in both plasma and urine. Here we describe a rapid HPLC/MS/MS method for these measurements using a normal phase HILIC column after analyte derivatization.
