Description:

This test is designed to assess abnormalities in the synthesis of creatine. Three disorders in the synthesis and transport of creatine have been recognized recently. Guanidinoacetate methyltransferase (GAMT) deficiency was the first inborn error of creatine biosynthesis in man. More recently, arginine:glycine amidinotransferase (AGAT) and creatine transporter deficiencies have been reported. GAMT deficiency results in creatine and creatine phosphate deficiency and leads to an elevation of guanidinoacetate in physiological fluids. The other disorders may also lead to alterations in the levels of these metabolites in physiological fluids. Guanidinoacetate and creatine are determined quantitatively by tandem mass spectroscopy .

Specimen Requirements:

This test is performed on plasma or urine. For plasma specimen, draw blood in a heparinized (green top) tube. Spin down and send 1 ml frozen plasma in an appropriate vial.  For urine, send 1 ml of a random urine. Do not add preservatives. Store the sample frozen and ship on dry ice.

Normal Range:

Plasma - Creatine: 0-1 yr, 30-120 micromoles/L; 2-18 yr, 20-110 micromoles/L
Plasma - Guanidinoacetate: 0-1 yr, 0.4-4.0 micromoles/L; 2-18 yr, 0.4-3.7 micromoles/L
Urine - Creatine: 0-5 yr, 20-900 mmoles/mole creatine; 6-18 yr, 12-500 mmoles/mole creatinine
Urine - Guanidinoacetate: 0-5, 10-130 mmoles/mole creatine; 6-18 yr, 2-114 mmoles/mole creatinine

Turnaround Time:

10 days

CPT Codes and Prices:

Plasma: 83789x2
Urine: 82570, 83789x2

Shipping Information

Forms:

>> Biochemical Requisition

Test Codes:

Plasma: 4130
Urine: 4260

Medical Genetics Laboratories
Baylor College of Medicine · Houston, TX 77030
Phone: 1-800-411-GENE · Fax: 713-798-6584
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