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Creatine and Guanidinoacetate (Plasma)
This assay is not currently available in New York state.
Expected Turnaround Time
10 - 14 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Lavender-top (EDTA) tube, green-top (sodium heparin) tube
Collect 2-4 mL blood in sodium heparin (green-top) or EDTA (purple-top) tube.
Remove plasma and freeze at -20°C. Store frozen at -20°C and ship frozen.
Causes for Rejection
Evaluation of patients with a clinical suspicion of inborn errors of creatine metabolism including arginine:glycine amidinotransferase deficiency, guanidinoacetate methyltransferase deficiency, and creatine transporter (SLC6A8) defect. Plasma/serum creatine and guanidinoacetate testing may also be used for assessment of Variants of Uncertain Significance (VUS) identified during genetic testing (e.g. Next Generation Sequencing or Capillary Sequencing testing). Disorders of creatine synthesis (deficiency of arginine:glycine amidinotransferase [AGAT] and guanidinoacetate methyltransferase [GAMT]) and creatine transporter (SLC6A8) deficiency are collectively described creatine deficiency syndromes (CDS). AGAT and GAMT deficiencies are inherited in an autosomal recessive manner, while the creatine transporter defect is X-linked. Diagnosis is possible by measuring guanidinoacetate (GAA), creatine (Crn) in plasma and urine. The profiles are specific for each clinical entity. Patients with GAMT deficiency typically exhibit normal to low Cr, very elevated GAA, and low Crn. Patients with AGAT deficiency typically exhibit normal to low Cr, low GAA, and normal to low Crn. In comparison, elevated Cr, normal GAA, normal to low Crn, and an elevated Cr:Crn ratio characterize patients with creatine transporter defect. AGAT, GAMT and the creatine transporter defect result in a depletion of of cerebral creatine and typically present with global developmental delays, intellectual disability, and severe speech delay. Some patients with CDS develop seizures. Patients with GAMT and the creatine transporter deficiency exhibit behavioral problems and features of autism. Female carriers for the creatine transporter deficiency can have intellectual disability and behavioral problems, and some develop seizures. Treatment with oral supplementation of creatine monohydrate is available and effective for the AGAT and GAMT deficiencies. Creatine supplementation has not been shown to improve outcomes in males with the creatine transporter defect. Female carriers of creatine transporter deficiency who have symptoms, however, have been reported to benefit from creatine supplementation.
This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|620180||Creatine and GAA Plasma||79289-5||230163||Specimen Status||N/A|
|620180||Creatine and GAA Plasma||79289-5||620174||Creatine Result||15045-8|
|620180||Creatine and GAA Plasma||79289-5||620189||Guanidinoacetate Result||33244-5|
|620180||Creatine and GAA Plasma||79289-5||620175||Interpretation||79291-1|