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Test ID GAL1P Galactose-1-Phosphate (Gal-1-P), Erythrocytes

Useful For

Monitoring dietary therapy of patients with galactosemia due to deficiency of galactose-1-phosphate uridyltransferase or uridine diphosphate galactose-4-epimerase

Genetics Test Information

This test is used to monitor dietary therapy of patients with galactosemia due to deficiency of galactose-1-phosphate uridyltransferase or uridine diphosphate galactose-4-epimerase.


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.

To diagnose epimerase deficiency, order GALE / UDP-Galactose 4' Epimerase, Blood.


Galactose-1-phosphate uridyltransferase (GALT) deficiency is the most common cause of galactosemia and requires lifelong restriction of dietary galactose.


This assay is used to monitor dietary compliance for patients with galactose-1-phosphate uridyltransferase (GALT) deficiency or uridine diphosphate galactose-4-epimerase (GALE) deficiency.

Special Instructions

Method Name

Ultraviolet, Enzymatic

Reporting Name

Galactose-1-Phosphate, RBC

Specimen Type

Washed RBC

Specimen Required

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:

1. For infants, collect specimen immediately prior to feeding to avoid postprandial elevations.

2. 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.

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time
Washed RBC Frozen 9 days

Reference Values

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)

Day(s) and Time(s) Performed

Tuesday; 8 a.m.

Performing Laboratory

Mayo Medical Laboratories in Rochester

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
GAL1P Galactose-1-Phosphate, RBC In Process


Result ID Test Result Name Result LOINC Value
80337 Galactose-1-Phosphate, RBC 33360-9
24101 Galactose-1-Phosphate Conversion 2312-7

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.

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions