Rapid LC-MS/MS Method for Targeted Assay of Creatine Deficiency Syndromes in Morocco

Background: Creatine deficiency syndromes (CDS) are rare neurometabolic disorders caused by defects in creatine biosynthesis (AGAT and GAMT deficiencies) or creatine transport (SLC6A8 deficiency). Early biochemical recognition is crucial for timely treatment of AGAT and GAMT deficiencies and for improving neurodevelopmental outcomes. In Morocco, expanding the liquid chromatography-tandem mass spectrometry (LC-MS/MS) biomarker panel for inherited metabolic disorders is a priority to strengthen diagnostic capacity and reduce diagnostic delay. Methods: We developed and validated a rapid LC-MS/MS method for the simultaneous quantification of creatine (Cr), guanidinoacetate (GAA), and creatinine (Crn) in plasma and urine using isotopically labelled internal standards and a standardized sample preparation procedure. Analytical performance, including linearity, precision, accuracy, sensitivity, matrix effects, carryover, inter-sample contamination, stability, and measurement uncertainty, was assessed in accordance with ISO 15189:2022 requirements. Results: The assay showed excellent linearity across the analytical range (r² > 0.99), with robust intra- and inter-day precision (CV < 10%). Limits of detection (LOD) were 0.05 µmol/L for Cr and 0.03 µmol/L for GAA in urine, and 0.05 µmol/L for Cr and GAA in plasma. The total run time was 1.1 min per sample, supporting high-throughput implementation. Method performance was further supported by satisfactory results in ERNDIM external quality assessment schemes. Preliminary internal reference ranges and expanded measurement uncertainty were calculated from the available anonymized dataset. Conclusions: This rapid LC-MS/MS method enables the measurement of key CDS biomarkers and contributes to expanding the LC-MS/MS biomarker panel for inherited metabolic disorders in Morocco.