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Test Code GCT Galactosemia Reflex, Blood

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Preferred test for diagnosis, carrier detection, and determination of genotype of galactose-1-phosphate uridyltransferase deficiency, the most common cause of galactosemia

 

Differentiating Duarte variant galactosemia from classic galactosemia

 

Confirming results of newborn screening programs

Testing Algorithm

Testing begins with galactose-1-phosphate uridyltransferase (GALT) enzyme analysis. If GALT is greater than or equal to 24.5 nmol/h/mg of hemoglobin, testing is complete. No molecular test will be performed. If GALT is less than 24.5 nmol/h/mg of hemoglobin, GAL14 / Galactosemia Gene Analysis (14-Mutation Panel) will be performed at an additional charge.

 

See Galactosemia Testing Algorithm in Special Instructions.

Method Name

Enzyme Reaction Followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Galactosemia Reflex, B

Specimen Type

Whole Blood EDTA


Specimen Required


Container/Tube: 

Preferred: Lavender top (EDTA)

Acceptable: Yellow top (ACD)

Specimen Volume: 5 mL

Additional Information: Patient's age is required.


Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Refrigerated (preferred) 28 days
  Ambient  14 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

NA

Icterus

NA

Other

NA

Reference Values

≥24.5 nmol/h/mg of hemoglobin

Interpretation

The laboratory provides an interpretation of the results, including galactose-1-phosphate uridyltransferase enzyme activity and genotype, if necessary. This interpretation provides an overview of the results and their significance, a correlation to available clinical information, elements of differential diagnosis, and recommendations for additional testing.

 

Any specimen where enzyme activity is less than 24.5 nmol/h/mg of hemoglobin will be analyzed for the presence of 14 mutations associated with classic galactosemia, as well as the 2 variants (Duarte and Los Angeles). See Galactosemia Reflex Algorithm in Special Instructions for testing algorithm and additional information.

 

The GALT gene maps to 9p13. Several disease-causing mutations are common in patients with classic galactosemia (G/G genotype). The most frequently observed is the Q188R classic mutation. This mutation accounts for 60% to 70% of classical galactosemia alleles. The S135L mutation is the most frequently observed mutation in African Americans and accounts for approximately 50% of the mutant alleles in this population. The K285N mutation is common in those of eastern European descent and accounts for 25% to 40% of the alleles in this population. The L195P mutation is observed in 5% to 7% of classical galactosemia. The 5-kb deletion is common in individuals of Ashkenazi Jewish descent. The Duarte mutation (N314D and -119_-116delGTCA) is observed in 5% of the general United States population. The rest of the mutations detected by this method (ie, D98N, S135L, T138M, M142K, F171S, Y209C, and Q344K) are all uncommon, but known to be recurrent in the general population.

 

A high proportion (20%) of patients with classic galactosemia have a private mutation. Since our assay does not investigate for the presence of private mutations, when GG, DG, or NG genotype is predicted by enzymatic studies and the current panel does not identify a mutation, molecular sequencing may be indicated.

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; 7 a.m. set up (specimen must arrive the day prior)

Analytic Time

4 days

Specimen Retention Time

2 months

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

Galactose-1-Phosphate Uridyltransferase (GALT), Blood

82775

 

Galactosemia Gene Analysis (14-Mutation Panel)

81401-GALT (galactose-1-phosphate uridylyltransferase) (eg, galactosemia), common variants (eg, Q188R, S135L, K285N, T138M, L195P, Y209C, IVS2-2A->G, P171S, del5kb, N314D, L218L/N314D

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GCT Galactosemia Reflex, B In Process

 

Result ID Test Result Name Result LOINC Value
8333 Gal-1-P Uridyltransferase, RBC 24082-0
2296 Interpretation (GALT) 59462-2
58115 Reviewed By 18771-6

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
GAL14 Galactosemia Gene Analysis Yes No

Forms

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.