Test Catalog

Test ID: GALK    
Galactokinase, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of galactokinase deficiency


Evaluation of children with unexplained bilateral congenital or juvenile onset cataracts

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Enzymatic testing for the diagnosis of galactokinase (GALK) deficiency.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Galactokinase (GALK) deficiency, is a very rare autosomal recessive disorder in the first step of galactose metabolism. Prevalence is unknown but estimated to be approximately 1 in 50,000-1 in 100,000 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 galactose-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 or urine 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 variants in the GALK1 gene. Gene analysis is available from some commercial laboratories. Call 800-533-1710 for recommendations or contact information for laboratories that offer this testing.


See Galactosemia Testing Algorithm in Special Instructions.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

> or =0.7 nmol/h/mg of hemoglobin

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided.


Deficient galactokinase (GALK) enzyme activity in erythrocytes is diagnostic for galactokinase deficiency.


See Galactosemia Testing Algorithm in Special Instructions for additional information.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The results of testing performed in erythrocytes, including analysis of enzymes, biochemical phenotyping, or galactose-1-phosphate are invalid following a transfusion.

Clinical Reference Recommendations for in-depth reading of a clinical nature

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. Accessed June 18, 2019. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62672411

Special Instructions Library of PDFs including pertinent information and forms related to the test