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Test Code GAL1P Galactose-1-Phosphate Uridyltransferase, Blood

Reporting Name

Gal-1-P Uridyltransferase, RBC

Useful For

Diagnosis of galactose-1-phosphate uridyltransferase deficiency, the most common cause of galactosemia

 

Confirmation of abnormal state newborn screening results

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Whole Blood EDTA


Advisory Information


This test is for galactose-1-phosphate uridyltransferase (GALT) enzyme testing only. The preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and followup of abnormal newborn screening results is GCT / Galactosemia Reflex, Blood.

 

This assay will not detect galactokinase (GALK) deficiency or uridine diphosphate-galactose 4' epimerase (GALE) deficiency.

-To evaluate for GALK deficiency, order GALK / Galactokinase, Blood.

-To evaluate for GALE deficiency, order GALE / UDP-Galactose 4' Epimerase, Blood.

 

This assay is not appropriate for monitoring dietary compliance. If dietary monitoring is needed, order GAL1P / Galactose-1-Phosphate, Erythrocytes.



Necessary Information


Patient's age is required.

  Biochemical Genetics Patient Information (T602) is recommended, but not required, to be filled out and sent with the specimen to aid in the interpretation of test results.

Specimen Required


Multiple whole blood tests for galactosemia can be performed on 1 specimen. Prioritize order of testing when submitting specimens. See Galactosemia-Related Test List in Special Instructions for a list of tests that can be ordered together.

 

Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: Green top (sodium heparin) or yellow top (ACD)

Specimen Volume: 5 mL


Specimen Minimum Volume

2 mL

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions.

Specimen Stability Information

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

Reference Values

≥24.5 nmol/h/mg of hemoglobin

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; 7 a.m. (specimen must be received the day prior)

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

82775

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GALT Gal-1-P Uridyltransferase, RBC 24082-0

 

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

Clinical Reference

1. Berry GT: Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by MP Adam, HH Ardinger, RA Pagon, et al. University of Washington, Seattle Updated 2017 Mar 9 Accessed: February 20, 2020 Available at https://www.ncbi.nlm.nih.gov/books/NBK1518/

2. Walter JH, Fridovich-Keil JL: Galactosemia. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. McGraw-Hill. Accessed June 18, 2019. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62672411

3. Carlock G, Fischer ST, Lynch ME, et al. Developmental Outcomes in Duarte Galactosemia. Pediatrics. 2018;143(1):e20182516. doi:10.1542/peds.2018-2516

Method Description

An aqueous mixture containing CLR H2O, uridine diphosphate (UDP)-glucose, (13)C2-labeled galactose-1-phosphate, and UDP-n-acetylglucosamine (internal standard) is added to a hemolysate aliquot. The mixture is then vortexed briefly and incubated at 37° C for 15 minutes.

 

After incubation the reaction is quenched, extracted, and centrifuged The top  layer is then transferred to a 96-well (Nunc, polypropylene) plate. Then injected onto a liquid chromatography-tandem mass spectrometry (LC-MS/MS) The ratio of the extracted peak area of (13)C2labeled UDP-galactose to its internal standard UDP-n-acetylglucosamine as determined by LC-MS/MS is used to calculate the concentration of product analyte in the sample. The concentration of the product is then normalized using the calculated hemoglobin concentration to determine the patient's enzyme level in nmol/h/mg of hemoglobin.(Unpublished Mayo method)

Analytic Time

4 days (not reported on Saturday or Sunday)

Reject Due To

Gross hemolysis Reject

Method Name

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

Forms

1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602) is recommended, see Special Instructions.

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

Secondary ID

8333