GC/MS determination of guanidinoacetate and creatine in urine: A routine method for creatine deficiency syndrome diagnosis.

OBJECTIVES: To further facilitate the diagnosis of creatine deficiency syndromes (CDS) a modified method was developed for the quantification of urinary creatine and guanidinoacetoacetate using gas chromatography/mass spectrometry (GC/MS) and having the additional advantage of using the same derivatizing agents, column and equipment usually used for the diagnosis of the organic acidurias in the clinical biochemistry laboratories.
MATERIAL AND METHODS: Guanidinoacetic acid, creatine standard solutions and pooled urines and pathological samples were used to validate a new and simple GC/MS technique modified from reported methods; its accuracy was assessed by comparing with liquid chromatography-electrospray tandem mass spectrometry (HPLC-MS/MS) method.
RESULTS: The method is precise: intra assay and inter assay variability for low and high concentrations were 3%, 6.4%/1.4%, 6.9% for creatine and 1.4%, 6.4%/0.9%, 6.9% for guanidinoacetoacetate. Agreement with HPLC/MS-MS method is good.
CONCLUSION: The GC/MS modified method is fast, reliable and practical for the diagnosis of CDS using the same means as those for organic acidurias diagnosis.