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Test ID GALP Galactose, Quantitative, Plasma

Reporting Name

Galactose, QN, P

Useful For

Screening for galactosemia

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Specimen Type

Plasma Na Heparin


Advisory Information


This test is not recommended for follow-up of positive newborn screening results or for diagnosis of galactosemia. The preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and followup of abnormal newborn screening results is GCT / Galactosemia Reflex, Blood along with GAL1P / Galactose-1-Phosphate, Erythrocytes.

 

The preferred test for monitoring dietary therapy is GAL1P / Galactose-1-Phosphate, Erythrocytes.



Necessary Information


Biochemical Genetics Patient Information (T602) is recommended, but not required, to be filled out and sent with the specimen to aid in the interpretation of test results.



Specimen Required


Collection Container/Tube: Green top (sodium heparin)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL


Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Na Heparin Frozen (preferred) 365 days
  Ambient  20 days
  Refrigerated  20 days

Reference Values

≤7 days: <5.4 mg/dL

8-14 days: <3.6 mg/dL

≥15 days: <2.0 mg/dL

Day(s) and Time(s) Performed

Tuesday; am

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

82760

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GALP Galactose, QN, P 2308-5

 

Result ID Test Result Name Result LOINC Value
83638 Galactose, QN, P 2308-5

Clinical Information

Galactosemia is an autosomal recessive disorder that results from a deficiency of any 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). GALT deficiency is the most common cause of galactosemia and is often referred to as classic galactosemia. The complete or near-complete deficiency of GALT enzyme is life-threatening if left untreated. Complications in the neonatal period include failure to thrive, liver failure, sepsis, and death.

 

Galactosemia is treated by a galactose-restricted diet, which allows for rapid recovery from the acute symptoms and a generally good prognosis. Despite adequate treatment from an early age, individuals with galactosemia remain at increased risk for developmental delays, speech problems, and abnormalities of motor function. Females with galactosemia are at increased risk for premature ovarian failure. Based upon reports by newborn screening programs, the frequency of classic galactosemia in the United States is 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.

 

A comparison of plasma and urine galactose and blood galactose-1-phosphate (Gal-1-P) levels may be useful in distinguishing among the 3 forms of galactosemia.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Interpretation

Additional testing is required to investigate the cause of abnormal results.

 

In patients with galactosemia, elevated galactose in plasma or urine may suggest ineffective dietary restriction or compliance; however, the concentration of galactose-1-phosphate in erythrocytes (GAL1P / Galactose-1-Phosphate, Erythrocytes) is the most sensitive index of dietary control. Increased concentrations of galactose may also be suggestive of severe hepatitis, biliary atresia of the newborn, and, in rare cases, galactose intolerance.

 

If results are outside the normal range and galactosemia is suspected, additional testing to identify the specific enzymatic defect is required. Results should be correlated with clinical presentation and confirmed by specific enzyme or molecular analysis. See Galactosemia Testing Algorithm in Special Instructions for follow-up of abnormal newborn screening results, comprehensive diagnostic testing, and carrier testing. See Advisory Information for test ordering guidance.

Clinical Reference

1. Berry GT: Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al. Updated 2017 March 9. Accessed February 20, 2020. Available at www.ncbi.nlm.nih.gov/books/NBK1518/

2. 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

Analytic Time

8 days

Method Name

Spectrophotometric, Kinetic

Forms

1. Biochemical Genetics Patient Information (T602) is recommended, see Special Instructions.

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