Use

This test provides quantitative analysis of creatine and guanidinoacetate in plasma; it is useful for the evaluation of patients with clinical suspicion of inborn errors of creatine metabolism such as guanidinoacetate methyltransferase deficiency (GAMT deficiency) and arginine: glycine amidinotransferase deficiency (AGAT deficiency). Creatine deficiency syndromes are characterized by intellectual disability, severe disturbance of expressive and cognitive speech, seizures (often poorly controlled), and movement disturbances. A common hallmark is cerebral creatine depletion as detected by magnetic resonance spectroscopy. In individuals with AGAT deficiency, both plasma and urine testing reveal low guanidinoacetate (GAA) and normal-low creatine concentrations. In GAMT deficiency, elevated plasma or urine GAA levels and normal-low creatine concentrations are characteristic. We recommend that Urine Creatine and Guanidinoacetate Determination (test code 4260) is ordered concurrently with this test.