Creatine and Guanidinoacetate (Urine)

CPT: 82540; 82542
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Special Instructions

This assay is not currently available in New York state.

Expected Turnaround Time

10 - 14 days

Specimen Requirements


Urine, frozen


1.0 mL

Minimum Volume

0.5 mL


Sterile cup


Collect entire sample into a single sterile cup.

Storage Instructions

Freeze as soon as possoble after collection; ship within 24 hours.

Stability Requirements



Room temperature






Causes for Rejection

Thawed sample

Test Details


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. Urine 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
620170 Creatine and GAA Urine 620171 Creatine Result 34275-8
620170 Creatine and GAA Urine 620190 Guanidinoacetate Result 34155-2
620170 Creatine and GAA Urine 620172 Interpretation 79292-9
620170 Creatine and GAA Urine 630854 PDF 80563-0
Reflex Table for Creatine Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 000000
Reflex Table for Guanidinoacetate Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 000000
Reflex Table for Interpretation
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 000000
Reflex Table for PDF
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 000000

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