Test ID: GALTP
Galactose-1-Phosphate Uridyltransferase Biochemical Phenotyping, Erythrocytes
NY State Approved 
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Determining the biochemical phenotype for galactosemia when enzymatic and molecular results are incongruent
A quantitative galactose-1-phosphate uridyltransferase level (GALT/8333 Galactose-1-Phosphate Uridyltransferase [GALT], Blood) is required for accurate interpretation.
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
.
Additional Tests Lists test(s) that are always performed, at an additional charge, with the initial test(s)
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| GALT | Gal-1-P Uridyltransferase, RBC | Yes | Yes |
Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
A quantitative galactose-1-phosphate uridyltransferase (GALT) level (GALT/8333 Galactose-1-Phosphate Uridyltransferase [GALT], Blood) is used in addition to the isoelectric focusing for accurate interpretation. If recent GALT test results are not provided, GALT will be automatically performed at an additional charge. However, if previous GALT results are provided, GALT testing will be cancelled and not charged.
See Galactosemia Testing Algorithm in Special Instructions.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
GALTP/80341: Isoelectric Focusing
GALT/8333: Ultraviolet, Kinetic
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Erythrocyte Galactose-1-Phosphate Uridyltransferase (GALT) Phenotyping
Galactose-1-Phosphate Uridyltransferase Isoenzymes/Isoelectric Focusing
Galactosemia
GALT Phenotype
GPUT (Galactose-1-Phosphate Uridyltransferase) Phenotyping
RBC (Red Blood Cell), Galactose-1-Phosphate Uridyltransferase Phenotyping
Galactose-1-Phosphate Uridyltransferase (GALT)
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube: Lavender top (EDTA)
Specimen Volume: 3 mL
Additional Information: Patient's age is required.
Forms:
1. 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 (Supply T576) is available in Special Instructions.
2. 2. If not ordering electronically, submit a Biochemical Genetics Request Form (Supply T439) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole Blood EDTA | Refrigerated (preferred) | 28 days |
| Ambient | 14 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Galactosemia is an autosomal recessive disorder that results from a deficiency of 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; even with survival, long-term intellectual disability can result. 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 approximately 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.
Duarte-variant galactosemia (compound heterozygosity for the Duarte mutation, N314D, and a classic mutation) is generally associated with higher levels of enzyme activity (5%-20%) than classic galactosemia (<5%); however, this may be indistinguishable by newborn screening assays. Typically, individuals with Duarte-variant galactosemia have a milder phenotype, but are also often treated with a low galactose diet during infancy. The LA variant, which consists of N314D and a second mutation, L218L, is associated with higher levels of GALT enzyme activity than the Duarte-variant allele.
In general, molecular genetic analysis with a panel of common mutations is typically performed to determine the specific genotype. If the enzymatic and molecular results are incongruent, biochemical phenotyping and/or molecular sequence analysis may be beneficial to help clarify results to determine a treatment strategy and recurrence risks.
For more information regarding diagnostic strategy, refer to Galactosemia: Current Testing Strategy and Aids for Test Selection, Mayo Medical Laboratories Communique 2005 May;30(5).
See Galactosemia Testing Algorithm in Special Instructions for additional information.
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.
Descriptive report
Interpretation Provides information to assist in interpretation of the test results
An interpretive report will be provided.
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
A more comprehensive interpretation can be provided when parental specimens are also submitted for testing.
Since transfusion results in replacement of significant number of red cells, the assay should be deferred for 90 days post-transfusion.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Elsas LJ: Galactosemia. NCBI GeneReviews. Updated 2010, Oct 26. Available from www.ncbi.nlm.nih.gov/books/NBK1518
2. Holton JB, Walter JH, Tyfield LA: Galactosemia. In The Metabolic and Molecular Basis of Inherited Disease. Vol. 1. 8th edition. Edited by CR Scriver, AL Beaundet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 1553-1587
Method Description Describes how the test is performed and provides a method-specific reference
Isoelectric focusing is used to resolve the isoenzymes of galactose-1-phosphate uridyltransferase (GALT). The band patterns, when used in conjunction with a quantitative GALT result, can be used to predict the GALT phenotype of an individual.
In isoelectric focusing, a pH gradient is established across an agarose gel by adding a select mixture of amphoteric molecules to the gel and applying an electric field to the gel. Each protein (isoenzyme) has its own unique isoelectric point, a pH at which the net charge of the protein is equal to zero. Therefore, if a protein is applied to the gel, it will migrate through the pH gradient in the gel until it reaches its isoelectric point. There the protein will stop and "focus" into distinct bands.
In this procedure, an RBC hemolysate is focused on a 5% agarose gel containing ampholytes of a 5 to 7 pH range. The isoenzyme bands are then visualized by applying a substrate mixture that results in a series of reactions (shown below). The final product, nicotinamide adenine dinucleotide phosphate (NADPH; reduced form), is stained a blue-violet color when it reacts with phenazine methosulfate (PMS) and 3-(4-5 dimethylthiazol-2-yl)I-2,5-diphenyltetrazolium bromide (MTT). (Shin YS, Niedermeier HP, Endres W, et al: Agarose gel isoelectrofocusing of UDP-galactose pyrophosphorylase and galactose-1-phosphate uridyltransferase: developmental aspect of UDP-galactose pyrophosphorylase. Clin Chim Acta 1987;166:27-35, modified to acrylamide as described by Leclerc P, Forest JC: Electrophoretic determination of isoamylases in serum with commercially available reagents. Clin Chem 1982;28:37-40)
|
| GALT |
|
| Gal-1-P + UDP-Glu | -------------> | UDP-Gal + Glu-1-P |
|
| Phosphoglucomutase |
|
| Glu-1-P + Glu-1-6 diP | -------------> | Glu-1-6 diP + Glu-6-P |
|
| Glu-6-P-Dehydrogenase |
|
| Glu-6-P + NADP | -------------> | Ribose-5-P + CO(2) + NADPH |
| NADPH + MTT + PMS | -------------> | Blue Violet Stain |
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Thursday; 9 a.m.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
Galactose-1-Phosphate Uridyltransferase Biochemical Phenotyping, Erythrocytes
82664
Galactose-1-Phosphate Uridyltransferase (GALT), Blood
82775
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 80341 | Gal-1-Phos Urdyltrns Phenotype,RBC | 33780-8 |
| 34524 | Reviewed By | N/A |
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