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Test ID: GCT    
Galactosemia Reflex, Blood

Method Description Describes how the test is performed and provides a method-specific reference

Ninety mcL of an aqueous mixture containing CLR H(2)O, UDP-glucose, (13)C(2)-labeled galactose-1-phosphate, and UDP-n-acetylglucosamine (internal standard) is added to 30 mcL hemolysate aliquot. The mixture is then vortexed briefly and incubated while rotating at 225 RPM and 37 degrees C for 15 minutes. The enzyme GALT (EC will convert (13)C(2)-labeled galactose-1-phosphate to (13)C(2)-labeled UDP-galactose during a 15 minute incubation at 37 degrees C.


Enzyme reaction:

(13)C(2)-galactose-1-phosphate + UDP-glucose Ă   (13)C(2)-UDP-galactose + glucose-1-phosphate


After incubation the reaction is quenched and extracted with 250 mcL of acetonitrile, vortexing for 30 seconds on a multi-tube vortexer. The mixture is then centrifuged at 3,000 rpm for 15 minutes in an ambient centrifuge. The top acetonitrile extract layer is then transferred to a 96-well (Nunc, polypropylene) plate. Then 10 mcL is injected onto an LC-MS/MS API 3200 system for chromatographic separation and measurement of analytes. The MS/MS is operated in the multiple reaction monitoring (MRM) negative mode to follow the precursor to product species transitions for (13)C(2)-labeled UDP-galactose (567.0 to 322.9 m/z) and internal standard of UDP-n-acetylglucosamine (606.2 to 384.7 m/z). The ratio of the extracted peak area of (13)C(2)labeled UDP-galactose to its internal standard UDP-n-acetylglucosamine as determined by liquid chromatography-tandem mass spectrometry is used to calculate the concentration of product analyte in the sample. The concentration of the product is then normalized using the calculated hemoglobin concentration to determine the patient’s enzyme level in nmol/h/mg of hemoglobin.(Unpublished Mayo method)


A real-time PCR-based assay using the LightCycler detects 6 alterations: Q188R, L195P, S135L, K285N, L218L, and N314D.(Dobrowolski SF, Banas RA, Suzow JG, et al: Analysis of common mutations in the galactose-1-phosphate uridyl transferase gene. J Mol Diagn 2003;5:42-47)

Supplemental Report Indicates whether the report includes an additional document with charts, images or other enriched information


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.

Monday, Wednesday, Friday; 7 a.m. set up (specimen must arrive the day prior)

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.

4 days

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

5 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

2 months

Performing Laboratory Location The location of the laboratory that performs the test