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Plasma, Guanidinoacetic Acid (GAA) and Creatine
Test Code901651
CPT Codes
82540, 82542<br>This test is not available for Florida, New York, or Rhode Island patient testing<br>Restricted Client Code
Preferred Specimen
1 mL plasma collected in a sodium heparin (green-top) tube
Minimum Volume
0.2 mL
Other Acceptable Specimens
EDTA (lavender-top) tube
Instructions
Same day delivery on ice or frozen specimens on dry ice by overnight deliver preferred.
Please note: Test name at Kennedy Krieger is "Quantification of Guanidinoacetate and Creatine"
Please note: Test name at Kennedy Krieger is "Quantification of Guanidinoacetate and Creatine"
Transport Temperature
Frozen
Specimen Stability
Room temperature: 24 hours
Refrigerated: 48 hours
Frozen: Indefinitely
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Frozen whole blood
Methodology
Gas Chromatography Mass Spectrometry
Setup Schedule
Set up: Mon, Thurs; Report available: 3-5 days
Reference Range
See Laboratory Report
Clinical Significance
Measurement of plasma and urine guanidinoacetic acid and creatine is useful for the diagnosis of creatine deficiency syndromes.
Arginine: Glycine amidinotransferase (AGAT) deficiency: Low GAA; Low Creatine, pl, ur, CSF
Guanidinoacetate methyltransferase (GAMT) deficiency: High GAA; Low Creatine, pl, ur, CSF
X-Linked dominant creatine transporter deficiency: Increased urine creatine/creatinine ratio
In the majority of cases of AGAT and GAMT deficiency, abnormal plasma GAA and creatine profiles are diagnostic. However, abnormal urine profiles should be confirmed by additional testing (plasma GAA and creatine levels, MR spectroscopy, mutation analysis). In addition, urine GAA levels may not be informative in the neonatal period.
All suspected cases of X-Linked dominant creatine transporter deficiency should be confirmed by MR spectroscopy and/or mutation analysis, as other factors may cause an increased creatine/creatinine ratio, including low muscle mass, renal tubular disease, or collection of a nonfasting sample.
Low plasma creatine levels may also be seen in patients with ornithine-delta-aminotransferase (OAT) deficiency (Gyrate Atrophy of the Choroid and Retina).
Arginine: Glycine amidinotransferase (AGAT) deficiency: Low GAA; Low Creatine, pl, ur, CSF
Guanidinoacetate methyltransferase (GAMT) deficiency: High GAA; Low Creatine, pl, ur, CSF
X-Linked dominant creatine transporter deficiency: Increased urine creatine/creatinine ratio
In the majority of cases of AGAT and GAMT deficiency, abnormal plasma GAA and creatine profiles are diagnostic. However, abnormal urine profiles should be confirmed by additional testing (plasma GAA and creatine levels, MR spectroscopy, mutation analysis). In addition, urine GAA levels may not be informative in the neonatal period.
All suspected cases of X-Linked dominant creatine transporter deficiency should be confirmed by MR spectroscopy and/or mutation analysis, as other factors may cause an increased creatine/creatinine ratio, including low muscle mass, renal tubular disease, or collection of a nonfasting sample.
Low plasma creatine levels may also be seen in patients with ornithine-delta-aminotransferase (OAT) deficiency (Gyrate Atrophy of the Choroid and Retina).
