Test ID: GAL1P
Galactose-1-Phosphate (Gal-1-P), Erythrocytes
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
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
Monitoring dietary therapy of patients with galactosemia due to galactose-1-phosphate uridyltransferase deficiency or uridine diphosphate galactose-4-epimerase deficiency
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
Monitoring dietary therapy of patients with galactosemia due to GALT or GALE deficiency. To diagnose galactosemia, order GCT/84360 Galactosemia Reflex, Blood.
Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
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
Ultraviolet, Enzymatic
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
Galactokinase
Galactose-1-Phosphate (Question if test number is not indicated by client)
Galactosemia
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.
Erythrocytes must be washed within 4 hours of draw.
Collection Container/Tube: Green top (heparin)
Submission Container/Tube: Plastic vial
Specimen Volume: Washed, packed cells (red cell pellet from step f in Collection Instructions)
Collection Instructions:
1. Collect and process a minimum of 2 mL of whole blood as follows:
a. Immediately centrifuge for 10 minutes at 650 x G. For conversion to RPMs, see Additional Information.
b. Discard the plasma and buffy coat layers.
c. Add a cold 0.9% saline solution to the erythrocytes (about 2 times the volume of erythrocytes).
d. Mix gently by inversion and centrifuge again for 10 minutes at 650 x G.
e. Remove and discard the saline.
f. Repeat the wash steps (steps c-e) 2 more times.
2. After the final centrifugation, remove and discard the saline and a thin layer of the top cells.
Additional Information:
The relative centrifugal force (G-force) can be estimated by applying the following formula: g=11.18 x r x (n/1000)2.
Where: r=radius in centimeters and n=speed in RPM.
The radius from the center of the rotation axis to the bottom or outermost portion of the test tube should be used. RCF is expressed relative to the force of the earth's gravity.
Forms: 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 | NA |
| 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 |
|---|---|---|
| Washed RBC | Frozen | 9 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.
Galactose-1-phosphate (Gal-1-P) accumulates in the erythrocytes of patients with galactosemia. The quantitative measurement of Gal-1-P is useful for monitoring compliance with and effectiveness of dietary therapy. Gal-1-P is thought to be the causative factor for development of liver disease in these patients and, because of this, patients should maintain low levels and be monitored on a regular basis. The concentration of Gal-1-P in erythrocytes is the most sensitive index of dietary control.
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.
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.
Non-galactosemic: 5-49 mcg/g of hemoglobin (<1 mg/dL)
Galactosemic on galactose restricted diet: 80-125 mcg/g of hemoglobin (1-4 mg/dL)
Galactosemic on unrestricted diet: >125 mcg/g of hemoglobin (>4 mg/dL)
Interpretation Provides information to assist in interpretation of the test results
The concentration of galactose-1-phosphate (Gal-1-P) is provided along with reference ranges for patients with galactosemia and normal controls. The recommended Gal-1-P goal for patients with galactosemia is <125 mcg/g of hemoglobin.
See Galactosemia Testing Algorithm in Special Instructions.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Not a diagnostic test for galactosemia; to diagnose galactosemia, order GCT/84360 Galactosemia Reflex, Blood.
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 Bases of Inherited Disease. 8th edition. Edited by CR Scriver, AL Beaudet, D Valle, et al. New York, McGraw-Hill Book Company, 2001, pp 1553-1587
3. Gitzelmann R: Estimation of galactose-1-phosphate in erythrocytes: a rapid and simple enzymatic method. Clin Chim Acta 1969;26:313-316
Method Description Describes how the test is performed and provides a method-specific reference
Galactose-1-phosphate (Gal-1-P) levels in RBCs are measured enzymatically in a 2-part reaction. In the first reaction aliquot, galactose dehydrogenase converts the endogenous galactose in the specimen to a galactonolactone, with the simultaneous production of nicotinamide adenine dinucleotide (NADH; reduced form) from nicotinamide adenine dinucleotide (NAD). The absorbance of NADH at 340 nm is used to determine the amount of galactose present in the specimen. In the second reaction aliquot, both alkaline phosphatase and galactose dehydrogenase are added. The alkaline phosphatase converts Gal-1-P into galactose and the galactose dehydrogenase converts the galactose into the galactonolactone, while producing NADH. The absorbance of NADH at 340 nm represents the galactose and Gal-1-P present in the specimen. By subtracting the absorbance of the first reaction aliquot from that of the second reaction aliquot, the Gal-1-P level can be determined.
The Gal-1-P levels are reported per gram of hemoglobin. In the hemoglobin analysis, RBCs are combined with aqueous ammonia to form a compound that absorbs light at 540 nm. The Beer-Lambert Law is applied to calculate the hemoglobin concentration from the measured absorbance. (Gitzelmann R: Estimation of galactose-1-phosphate in erythrocytes; a rapid and simple enzymatic method. Clin Chim Acta 1969 November;26[2]:313-316)
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.
Wednesday; 8 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.
84378
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 |
|---|---|---|
| 80337 | Galactose-1-Phosphate, RBC | 33360-9 |
| 24101 | Galactose-1-Phosphate Conversion | 2312-7 |
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