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Test ID: GALE UDP-Galactose 4' Epimerase (GALE), Blood

Useful For

Diagnosis of UDP-galactose 4' epimerase deficiency

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Method Name

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

Reporting Name

UDP-galactose 4' epimerase, RBC

Specimen Type

Whole Blood EDTA

Advisory Information

This test is for diagnosis of UDP-galactose 4' epimerase (GALE) deficiency.


For diagnosis of galactokinase deficiency, see GALK / Galactokinase, Blood.


To evaluate for galactose-1-phosphate uridyltransferase deficiency, see GALT / Galactose-1-Phosphate Uridyltransferase, Blood.


This assay is not appropriate for monitoring dietary compliance; see GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.


This assay will not detect galactokinase deficiency (see GALK / Galactokinase, Blood) or galactose-1-phosphate uridyltransferase deficiency (see GALT / Galactose-1-Phosphate Uridyltransferase, Blood).

Necessary Information

Patient's age is required.

Specimen Required


Preferred: Lavender top (EDTA)

Acceptable: Green top (sodium heparin), green top (lithium heparin), or yellow top (ACD)

Specimen Volume: 5 mL

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Refrigerated (preferred) 14 days
  Ambient  6 days

Clinical Information

Galactosemia is an autosomal recessive disorder that results from a deficiency of 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). Epimerase deficiency galactosemia can be categorized into 3 types: generalized, peripheral, and intermediate. Generalized epimerase deficiency galactosemia results in profoundly decreased enzyme activity in all tissues, whereas peripheral epimerase deficiency galactosemia results in decreased enzyme activity in red and white blood cells, but normal enzyme activity in all other tissues. This is compared to intermediate epimerase deficiency galactosemia which results in decreased enzyme activity in red and white blood cells and less than 50% of normal enzyme levels in other tissues.


Clinically, infants with generalized epimerase deficiency galactosemia develop symptoms such as liver and renal dysfunction and mild cataracts when on a normal milk diet, while infants with peripheral or intermediate epimerase deficiency galactosemia do not develop any symptoms. Generalized epimerase deficiency galactosemia is treated by a galactose- and lactose-restricted diet, which can improve or prevent the symptoms of renal and liver dysfunction and mild cataracts. Despite adequate treatment from an early age, individuals with generalized epimerase deficiency galactosemia remain at increased risk for developmental delay and intellectual disability. Unlike patients with classic galactosemia resulting from a GALT deficiency, females with generalized epimerase deficiency galactosemia experience normal puberty and are not at increased risk for premature ovarian failure. Based upon reports by newborn screening programs, the frequency of epimerase deficiency galactosemia in the United States ranges from approximately 1 in 6,700 in African American infants to 1 in 70,000 infants of European ancestry.


Galactose-1-phosphate (Gal-1-P) accumulates in the erythrocytes of patients with galactosemia due to either GALT or GALE deficiency. The quantitative measurement of Gal-1-P (GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes) is useful for monitoring compliance with dietary therapy. Gal-1-P is thought to be the causative factor for development of liver disease in these patients and, because of this, patients should maintain low levels and be monitored on a regular basis.


Newborn screening, which identifies potentially affected individuals by measuring total galactose (galactose and Gal-1-P) and/or determining the activity of the GALT enzyme, varies from state to state. The diagnosis of galactosemia is established by follow-up quantitative measurement of GALT enzyme activity. If enzyme levels are normal, but an infant has an elevated Gal-1-P, then epimerase deficiency galactosemia is to be considered. Molecular testing via sequencing of the GALE gene may be performed.


See Galactosemia Testing Algorithm in Special Instructions for additional information.

Reference Values

≥3.5 nmol/h/mg of hemoglobin


An interpretive report will be provided.

Clinical Reference

1. Li Y, Huang X, Harmonay L, et al: Liquid chromatography-tandem mass spectrometry enzyme assay for UDP-galactose 4'-epimerase: use of fragment intensity ratio in differentiation of structural isomers. Clin Chem 2014;60:783-790

2. Chen J, Meyers GA, Bennett MJ: An interference-free two-step enzyme assay with UPLC-tandem mass spectrometric product measurement for the clinical diagnosis of uridine diphosphate galactose-4-epimerase deficiency. J Chromatogr B Analyt Technol Biomed Life Sci 2014;959:5-9

3. Fridovich-Keil J, Bean L, He M, et al: Epimerase Deficiency Galactosemia. In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al. Seattle, WA, University of Washington, Seattle; 1993-2015. Available at

Day(s) and Time(s) Performed

Friday, 7 a.m. set up (specimen must be received the day prior)

Analytic Time

8 days (not reported on Saturday or Sunday)

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
GALE UDP-galactose 4' epimerase, RBC In Process


Result ID Test Result Name Result LOINC Value
64372 UDP-galactose 4' epimerase, RBC 79469-3
37979 Interpretation (GALE) 59462-2
37978 Reviewed By 18771-6


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) in Special Instructions.

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

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: