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HelpOrder Code LABGCT Galactosemia Reflex, Blood
Reporting Name
Galactosemia Reflex, BUseful 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
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| GALZ | Galactosemia, Full Gene Analysis | Yes | No |
Testing Algorithm
Testing begins with galactose-1-phosphate uridyltransferase (GALT) enzyme analysis. If GALT activity is greater than or equal to 24.5 nmol/h/mg of hemoglobin, testing is complete. No molecular test will be performed. If GALT activity is less than 24.5 nmol/h/mg of hemoglobin, galactosemia full gene sequencing will be performed at an additional charge.
For more information see Galactosemia Testing Algorithm
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Whole Blood EDTAOrdering Guidance
This test is appropriate for the diagnosis of, and routine carrier screening for, galactose-1-phosphate uridyltransferase deficiency.
This assay is not appropriate for monitoring dietary compliance. For dietary monitoring, order GAL1P / Galactose-1-Phosphate, Erythrocytes.
Necessary Information
Patient's age is required.
Specimen Required
Multiple whole blood tests for galactosemia can be performed on one specimen. Prioritize order of testing when submitting specimens. For a list of tests that can be ordered together, see Galactosemia-Related Test List.
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium heparin) or yellow top (ACD)
Specimen Volume: 5 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Specimen Minimum Volume
2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole Blood EDTA | Refrigerated (preferred) | 28 days | |
| Ambient | 14 days |
Special Instructions
Reference Values
≥24.5 nmol/h/mg of hemoglobin
Day(s) Performed
Monday, Wednesday, Friday
CPT Code Information
82775
81406 (if appropriate)
Genetics Test Information
Preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and follow-up of abnormal newborn screening results. Comprehensive reflex test begins with quantitative galactose-1-phosphate uridyltransferase (GALT) enzyme analysis. If quantitative GALT enzyme value is less than 24.5 nmol/h/mg of hemoglobin, full gene sequencing of the GALT gene is performed.
Method Description
Galactose-1-Phosphate Uridyltransferase Enzyme Analysis:
An aqueous mixture containing water, uridine diphosphate (UDP)-glucose, (13)C2-labeled galactose-1-phosphate, and UDP-N-acetylglucosamine (internal standard) is added to hemolysate aliquot. The mixture is then vortexed briefly and incubated.
After incubation, the reaction is quenched, extracted, and centrifuged. The top layer is transferred to a 96-well plate and then injected onto a liquid chromatography tandem mass spectrometry (LC-MS/MS). The ratio of the extracted peak area of (13)C2 labeled 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)
GALT Full Gene Sequencing:
Next-generation sequencing (NGS) and/or Sanger sequencing is performed to test for the presence of variants in coding regions and intron/exon boundaries of the GALT gene. NGS and/or a polymerase chain reaction (PCR)-based quantitative method is performed to test for the presence of deletions and duplications in the GALT gene.
There may be regions of GALT that cannot be effectively amplified for sequencing or deletion and duplication analysis because of technical limitations of the assay, including regions of homology, high guanine-cytosine content, and repetitive sequences. Confirmation of select reportable variants may be performed by alternate methodologies based on internal laboratory criteria.
PCR-based methods and/or Sanger sequencing is used to confirm variants detected by NGS when appropriate.(Unpublished Mayo method)
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:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. If not ordering electronically, complete, print, and send an Biochemical Genetics Test Request (T798) with the specimen.