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Test Code GALK Galactokinase, Blood

Reporting Name

Galactokinase, B

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)

Performing Laboratory

Mayo Medical Laboratories in Rochester

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


Container/Tube:

Preferred: Lavender top (EDTA)

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

Specimen Volume: 4 mL


Specimen Minimum Volume

2 mL

Specimen Stability Information

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

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

NA

Icterus

NA

Other

NA

Reference Values

≥0.7 nmol/h/mg of hemoglobin

Day(s) and Time(s) Performed

Mondays; 9 a.m.

CPT Code Information

82759

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 In Process

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.

Cautions

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.

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)

Analytic Time

8 days

Specimen Retention Time

2 months

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.

Interpretation

An interpretive report will be provided.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Forms

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.