LC-MS/MS measurements of urinary guanidinoacetic acid and creatine: Method optimization by deleting derivatization step

Background: Cerebral Creatine deficiency syndromes (CCDS) include three hereditary diseases affecting the metabolism of creatine (Cr): arginine glycine amidinotransferase deficiency, guanidinoacetate methyltransferase deficiency and disorders of creatine transporter. These pathologies cause a brain creatine deficiency responsible of non-specific neurological impairments with mental retardation. LC-MS/MS measurements of guanidinoacetic acid (GAA) and creatine in urine and plasma are an important screening test to identify the deficit. Analysis of this polar and basic molecules not hold on standard column requires a derivatization step to butyl-esters. To overcome this long and fastidious derivatization, an ion pairing (IP) method was chosen in this study. Method: IP method was validated using Comite francais d'accreditation (COFRAC) recommendations. Then, urine GAA and creatine of 15 patients with a CDS deficiency suspected were tested y LC-MS/MS using IP technique, and performances were assessed with reference laboratory method (butylation method). Moreover, references values were suggested y the study of 100 urines samples of healthy patients. Results: The method developed provided a good accuracy and precision with infra and inter-day coefficients of variation (CVs) < 15%. The curve was linear for the biological and pathological concentrations. The comparison with the reference method did not reveal any significant difference for analytical performances but showed a simplification of the preparation of samples. Conclusion: The use of IP technique that we have developed demonstrated a good correlation with the butylation method. Moreover, this new method not only allows a simplification of the technique, but also decreases in run time.