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Test Code GALTP Galactose-1-Phosphate Uridyltransferase Biochemical Phenotyping, Erythrocytes

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

Gal-1-Phos Urdyltrns Phenotype,RBC

Specimen Type

Whole Blood EDTA

Advisory Information

GCT / Galactosemia Reflex, Blood is the preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and follow-up of abnormal newborn screening results.


For monitoring of dietary compliance, see GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.

Necessary Information

Patient's age is required.

Specimen Required

Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Reject Due To


Mild OK; Gross reject







Specimen Stability Information

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

Specimen Minimum Volume

2 mL

Day(s) and Time(s) Performed

Thursday; 9 a.m.

Specimen Retention Time

Processed RBC stored 2 months

Analytic Time

8 days

Reference Values

Descriptive report

Additional Tests

Test ID Reporting Name Available Separately Always Performed
GALT Gal-1-P Uridyltransferase, RBC Yes Yes

Useful For

Determining the biochemical phenotype for galactosemia when enzymatic and molecular results are incongruent

Testing Algorithm

A quantitative galactose-1-phosphate uridyltransferase GALT) level is used in addition to the isoelectric focusing for accurate interpretation. If recent GALT test results are not provided, GALT will be automatically performed at an additional charge. However, if previous GALT results are provided, GALT testing will be cancelled and not charged.


See Galactosemia Testing Algorithm in Special Instructions.

Method Name

GALTP: Isoelectric Focusing
GALT: Enzyme Reaction Followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

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



LOINC Code Information

Test ID Test Order Name Order LOINC Value
GALTP Gal-1-Phos Urdyltrns Phenotype,RBC In Process


Result ID Test Result Name Result LOINC Value
80341 Gal-1-Phos Urdyltrns Phenotype,RBC 33780-8
34524 Reviewed By 18771-6

Clinical Information

Galactosemia is an autosomal recessive disorder that results from a deficiency of any 1 of the 3 enzymes catalyzing the conversion of galactose to glucose: galactose-1-phosphate uridyltransferase (GALT), galactokinase (GALK), and uridine diphosphate galactose-4-epimerase (GALE). GALT deficiency is the most common cause of galactosemia and is often referred to as classic galactosemia. The complete or near-complete deficiency of GALT enzyme is life-threatening if left untreated. Complications in the neonatal period include failure to thrive, liver failure, sepsis, and death; even with survival, long-term intellectual disability can result.


Galactosemia is treated by a galactose-restricted diet, which allows for rapid recovery from the acute symptoms and a generally good prognosis. Despite adequate treatment from an early age, individuals with galactosemia remain at increased risk for developmental delays, speech problems, and abnormalities of motor function. Females with galactosemia are at increased risk for premature ovarian failure. Based upon reports by newborn screening programs, the frequency of classic galactosemia in the United States is approximately 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.


Duarte-variant galactosemia (compound heterozygosity for the Duarte mutation, N314D, and a classic mutation) is generally associated with higher levels of enzyme activity (5%-20%) than classic galactosemia (<5%); however, this may be indistinguishable by newborn screening assays. Typically, individuals with Duarte-variant galactosemia have a milder phenotype, but are also often treated with a low galactose diet during infancy. The LA variant, which consists of N314D and a second mutation, L218L, is associated with higher levels of GALT enzyme activity than the Duarte-variant allele.


In general, molecular genetic analysis with a panel of common mutations is typically performed to determine the specific genotype. If the enzymatic and molecular results are incongruent, biochemical phenotyping and/or molecular sequence analysis may be beneficial to help clarify results to determine a treatment strategy and recurrence risks.


See Galactosemia Testing Algorithm in Special Instructions for additional information.


An interpretive report will be provided.


A quantitative galactose-1-phosphate uridyltransferase level (GALT / Galactose-1-Phosphate Uridyltransferase [GALT], Blood) is required for accurate interpretation.


See Galactosemia Testing Algorithm in Special Instructions for additional information.


A more comprehensive interpretation can be provided when parental specimens are also submitted for testing.


Since transfusion results in replacement of significant number of red cells, the assay should be deferred for 90 days posttransfusion.

Clinical Reference

1. Berry GT. Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by Pagon RA, Adam MP, Ardinger HH, et al. Available at Retrieved 03/11/2015

2. Walter JH, Fridovich-Keil JL: Galactosemia. In The Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill, 2014. Accessed January 26, 2016. Available at

Method Description

Isoelectric focusing is used to resolve the isoenzymes of galactose-1-phosphate uridyltransferase (GALT). The band patterns, when used in conjunction with a quantitative GALT result, can be used to predict the GALT phenotype of an individual.


In isoelectric focusing, a pH gradient is established across an agarose gel by adding a select mixture of amphoteric molecules to the gel and applying an electric field to the gel. Each protein (isoenzyme) has its own unique isoelectric point, a pH at which the net charge of the protein is equal to zero. Therefore, if a protein is applied to the gel, it will migrate through the pH gradient in the gel until it reaches its isoelectric point. There the protein will stop and "focus" into distinct bands.


In this procedure, an RBC hemolysate is focused on a 5% agarose gel containing ampholytes of a 5 to 7 pH range. The isoenzyme bands are then visualized by applying a substrate mixture that results in a series of reactions (shown below). The final product, nicotinamide adenine dinucleotide phosphate (NADPH; reduced form), is stained a blue-violet color when it reacts with phenazine methosulfate (PMS) and 3-(4-5 dimethylthiazol-2-yl)I-2,5-diphenyltetrazolium bromide (MTT).(Shin YS, Niedermeier HP, Endres W, et al: Agarose gel isoelectrofocusing of UDP-galactose pyrophosphorylase and galactose-1-phosphate uridyltransferase: developmental aspect of UDP-galactose pyrophosphorylase. Clin Chim Acta 1987;166:27-35, modified to acrylamide as described by Leclerc P, Forest JC: Electrophoretic determination of isoamylases in serum with commercially available reagents. Clin Chem 1982;28:37-40)





Gal-1-P + UDP-Glu


UDP-Gal + Glu-1-P




Glu-1-P + Glu-1-6 diP


Glu-1-6 diP + Glu-6-P




Glu-6-P + NADP


Ribose-5-P + CO(2) + NADPH



Blue Violet Stain


Disease States

  • Galactosemia


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. Biochemical Genetics Patient Information (T602) in Special Instructions.