Galactosemia, Non-Classic (Galactokinase Deficiency): GALK Enzyme Activity, Red Blood Cells

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This test has been temporarily discontinued, effective December 14, 2016. We do apologize for an inconvenience this may cause. Please contact a laboratory genetic counselor at (404)778-8499 for more information.

Condition Description

Galactosemia is an autosomal recessive disorder of galactose metabolism that often presents in the newborn period with poor suck, vomiting, diarrhea, bleeding diathesis, lethargy, jaundice, and sepsis. If left untreated, an individual may progress to irreversible liver disease and mental retardation.

Galactokinase deficiency should be considered in individuals with cataracts, elevated red cell galactose, galactosuria, or elevated urinary galactitol and normal GALT enzyme activity. Galactokinase converts galactose to galactose-1-phosphate. The deficiency results in the accumulation of galactose and urine galactitol.

Galactokinase activity is used to rule-out variant galactosemia due to galactokinase deficiency. Galactokinase deficiency should not be confused with classical Galactosemia secondary to GALT deficiency. Refer to Galactosemia: Comprehensive Panel (GS) for a disease overview.

Click here for the GeneReviews summary on this condition.

Visit for patient-friendly information on galactosemia.


This test is indicated in the case of:

  • Normal galactose-1-phosphate and normal GALT activity
  • Galactosemia with cataracts


Galactokinase is evaluated by measuring the enzyme's ability to convert galactose to galactose-1-phosphate using a radioenzymatic reaction.

Detection and Reference Range


Detection of reduced galactokinase activity is diagnostic of galactokinase deficient galactosemia.

Reference Range

0-2 yrs: 0.92 - 4.4 umol/hr/gm Hb
>3 yrs:  0.62 - 1.93 umol/hr/gm Hb

Specimen Requirements

Additional Specimen Collection/Handling Instructions Required for this Test
If whole blood specimen cannot be received by EGL within 24 hours of collection, send 2-3 ml washed RBC's. (Click here for protocol.) 

Ship washed RBC's frozen on dry ice with overnight delivery.  Please indicate on the requisition that the specimen type is washed RBC's. 

Type: Whole Blood

Specimen Requirements:

In sodium heparin (green top) tube: 3-5 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample overnight at room temperature for receipt at EGL within 24 hours of collection.

  • Galactitol (test code GL) - biochemical screening test for diagnosis and monitoring of patients with galactosemia.
  • Galctose-1-Phosphate (test code GP) - biochemical screening test for diagnosis and monitoring of patients with galactosemia.
  • Galactosemia:  Nonclassic Galactosemia Panel (GALK & GALE Enzymes and Galactose-1-Phosphate) (test code BGKEP).
  • Galactosemia (Galactokinase Deficiency): Full Gene Sequencing (test code IQ) - if the proband has a biochemical diagnosis of galactokinase deficiency. 
  • Custom Diagnositic Mutation Analysis (test code KM) is available to individuals.  Please contact the laboratory genetic counselor to arrange testing. 
  • Galactosemia (Galactokinase Deficiency): Deletion/duplication (test code JA) - when mutations are not detected by full gene sequencing. 
  • Prenatal testing is available by molecular methods.  Please contact the laboratory genetic counselor to determine the availability of prenatal testing. 

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