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Interpretive Handbook

Test 80337 :
Galactose-1-Phosphate (Gal-1-P), Erythrocytes

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.

Useful For Suggests clinical disorders or settings where the test may be helpful

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

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 for additional information.

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 / Galactosemia Reflex, Blood.

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)

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Berry GT: Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al. Available from URL http://www.ncbi.nlm.nih.gov/books/NBK1518/. Retrieved 03/11/2015

2. Walter JH, Fridovich-Keil JL: Chapter 72: Galactosemia. In The Metabolic and Molecular Bases of Inherited Disease. Eighth edition. Edited by D Valle. AL Beaudet, B Vogelstein. New York, McGraw-Hill Book Company. Available from URL http:// www.ommbid.com. Accessed 03/11/2015