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HelpMayo Test ID GALP Galactose, Quantitative, Plasma
Ordering Guidance
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 follow-up 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 for both GALT and GALE deficiencies.
This test may be useful for monitoring in patients with GALM deficiency.
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
Collection Instructions: Centrifuge and aliquot plasma into a plastic vial
Useful For
Screening for galactosemia
Testing Algorithm
For more information see Galactosemia Testing Algorithm.
Special Instructions
Method Name
Spectrophotometric/Kinetic
Reporting Name
Galactose, QN, PSpecimen Type
Plasma Na HeparinSpecimen 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 |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
Clinical Information
Galactosemia is an autosomal recessive disorder that results from a deficiency of any 1 of the 4 enzymes catalyzing the conversion of galactose to glucose: galactose-1-phosphate uridyltransferase (GALT), galactokinase (GALK), uridine diphosphate galactose-4-epimerase (GALE), and galactose mutarotase (GALM). 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. Female patients 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 (Gal1P) levels may be useful in distinguishing among the 4 forms of galactosemia.
|
Deficiency |
Galactose (plasma/urine) |
Gal1P (blood) |
|
GALK |
Elevated |
Normal |
|
GALT |
Elevated |
Elevated |
|
GALE |
Normal-Elevated |
Elevated |
|
GALM |
Elevated |
Normal-Elevated |
For more information see Galactosemia Testing Algorithm.
Reference Values
≤7 days: <5.4 mg/dL
8-14 days: <3.6 mg/dL
≥15 days: <2.0 mg/dL
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 for patients with galactose-1-phosphate uridyltransferase and uridine diphosphate galactose-4-epimerase deficiencies. 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. For follow-up of abnormal newborn screening results, comprehensive diagnostic testing, and carrier testing see Galactosemia Testing Algorithm. For more information see Ordering Guidance.
Cautions
No significant cautionary statements
Clinical Reference
1. Berry GT. Classic galactosemia and clinical variant galactosemia. In: Adam MP, Feldman J, Mirzaa GM, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2000. Updated March 11, 2021. Accessed September 12, 2024. Available at www.ncbi.nlm.nih.gov/books/NBK1518/
2. Walter JH, Fridovich-Keil JL. Galactosemia. In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed September 12, 2024. Available at https://ommbid.mhmedical.com/content.aspx?bookid=2709§ionid=%20225081023
3. Wada Y, Kikuchi A, Arai-Ichinoi N, et al. Biallelic GALM pathogenic variants cause a novel type of galactosemia. Genet Med. 2019;21(6):1286-1294. doi:10.1038/s41436-018-0340-x
4. Timson DJ. Type IV galactosemia. Genet Med. 2019;21(6):1283-1285. doi:10.1038/s41436-018-0359-z
Method Description
The formation of reduced nicotinamide adenine dinucleotide (NADH) measured by the increase in absorbance at 340 nm is proportional to the amount of D-galactose in the sample.(Kurz G, Wallenfels K. In: Bergmeyer HV, ed: Methods of Enzymatic Analysis. Vol 3. 2nd ed. Verlag Chemie, Weinheim, Academic Press. 1974:1279-1282; Cowan T, Pasquali M. Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw-Hill; 2017:1139-1158)
Day(s) Performed
Tuesday
Report Available
4 to 10 daysSpecimen Retention Time
1 monthPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US 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 |