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Test Code GALK Galactokinase, Blood

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

Galactokinase, B

Specimen Type

Whole Blood EDTA

Advisory Information

This test is for diagnosis of galactokinase (GALK) deficiency. The most common cause of galactosemia is GALT deficiency. In most cases, GALT deficiency should be ruled out prior to evaluating for galactokinase (GALK) deficiency (see GCT / Galactosemia Reflex, Blood).


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


This assay will not detect UDP-galactose 4' epimerase (GALE) deficiency or galactose-1-phosphate uridyltransferase (GALT) deficiency. For epimerase deficiency, see GALE / UDP-Galactose 4' Epimerase (GALE), Blood.


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

Specimen Required


Preferred: Lavender top (EDTA)

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

Specimen Volume: 4 mL

Reject Due To


Mild OK; Gross reject







Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Refrigerated (preferred) 10 days
  Ambient  72 hours

Specimen Minimum Volume

2 mL

Day(s) and Time(s) Performed

Mondays; 9 a.m.

Specimen Retention Time

2 months

Analytic Time

8 days

Reference Values

≥0.7 nmol/h/mg of hemoglobin

Useful For

Diagnosis of galactokinase deficiency, the second most common cause of galactosemia

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions.

Method Name

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
GALK Galactokinase, B 81143-0


Result ID Test Result Name Result LOINC Value
38005 Galactokinase, B In Process
38007 Interpretation (GALK) In Process
38006 Reviewed By 18771-6

Clinical Information

Galactokinase (GALK) deficiency is the second most common form of galactosemia, affecting approximately 1 in 250,000 live births, with a higher frequency in the Romani population. Individuals with GALK deficiency have a milder clinical presentation than that seen in patients with classic galactosemia, galactose-1-phosphate uridyltransferase (GALT) deficiency. The major clinical manifestation is bilateral juvenile cataracts.


GALK deficiency is treated with a lactose-restricted diet. Early treatment may prevent or reverse the formation of cataracts.


In GALK deficiency, erythrocyte galactose-1-phosphate levels are generally normal and plasma galactose levels are generally elevated. The diagnosis is established by demonstrating deficient GALK enzyme activity in erythrocytes. Testing for GALK deficiency should be performed when there is a suspicion of galactosemia, either based upon the patient's clinical presentation or laboratory studies and GALT deficiency has been excluded. Specimens sent for GALT analysis may be used for GALK testing if the original specimen was received in the laboratory within the stability parameters listed in Specimen Stability Information.


GALK deficiency is caused by mutations in the GALK1 gene. Gene analysis is available from some commercial laboratories. Contact Mayo Medical Laboratories for recommendations or contact information for laboratories that offer this testing.


See Galactosemia Testing Algorithm in Special Instructions.


An interpretive report will be provided.


See Galactosemia Testing Algorithm in Special Instructions for additional information.


It is important to notify the laboratory if the patient has been transfused prior to specimen collection. The results of testing performed in erythrocytes are invalid following a transfusion, including analysis of enzymes, biochemical phenotyping, or galactose-1-phosphate.

Clinical Reference

1. Li, Y, Ptolemy AS, Harmonay L, et al: Ultra fast and sensitive liquid chromatography tandem mass spectrometry based assay for galactose-1-phosphate uridylyltransferase and galactokinase deficiencies. Mol Gen Metab 2011;102(1):33-40

2. Ko DH, Jun SH, Park HD, et al: Multiplex enzyme assay for galactosemia using ultraperformance liquid chromatography-tandem mass spectrometry. Clin Chem 2010;56:764-771

3. Hennermann JB, Schadewaldt P, Vetter B, et al: Features and outcome of galactokinase deficiency in children diagnosed by newborn screening. J Inherit Metab Dis 2011;34:399-407

4. 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, New York, 2014, Accessed March 31, 2017. Available at:

Method Description

A buffered enzyme incubation with substrate and cofactors is performed on lysed red blood cells. A postincubation extraction is performed and subjected to liquid chromatography-tandem mass spectrometry. The ratio of the extracted product to its internal standard is used to calculate the total enzymatic product. This is then normalized using the calculated hemoglobin concentration to determine the patient's enzyme level in nmol/h/mg of hemoglobin.(Unpublished Mayo method)


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.