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Test Code GALP Galactose, Quantitative, Plasma

Reporting Name

Galactose, QN, P

Useful For

Screening for galactosemia

Testing Algorithm

This is a screening test only.


See Galactosemia Testing Algorithm in Special Instructions.

Method Name

Spectrophotometric, Kinetic

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Plasma Na Heparin

Advisory Information

This test is not recommended for follow-up of positive newborn screening results. For this purpose GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes and GCT / Galactosemia Reflex Test, Blood are the most appropriate tests.


This test is not appropriate for the diagnosis of galactosemia. For diagnosis, see GCT / Galactosemia Reflex, Blood.


The preferred test for monitoring dietary therapy is GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.

Specimen Required

Collection Container/Tube: Green top (sodium heparin)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Na Heparin Frozen (preferred) 365 days
  Ambient  20 days
  Refrigerated  20 days

Reject Due To

Gross hemolysis OK
Gross lipemia OK

Reference Values

≤7 days: <5.4 mg/dL

8-14 days: <3.6 mg/dL

≥15 days: <2.0 mg/dL

Day(s) and Time(s) Performed


CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
GALP Galactose, QN, P 2308-5


Result ID Test Result Name Result LOINC Value
83638 Galactose, QN, P 2308-5

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.

Disease States

  • Galactosemia

Clinical Information

Galactosemia is an autosomal recessive disorder that results from a deficiency of any 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 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.


A comparison of plasma and urine galactose and blood galactose-1-phosphate (Gal-1-P) levels may be useful in distinguishing among the 3 forms of galactosemia.


See Galactosemia Testing Algorithm in Special Instructions for additional information.



Galactose (Plasma/Urine)

Gal-1-P (Blood)











Additional testing is required to investigate the cause of abnormal results.


In patients with galactosemia, elevated galactose in plasma or urine may suggest ineffective dietary restriction or compliance; however, the concentration of galactose-1-phosphate in erythrocytes (GAL1P / Galactose-1-Phosphate [Gal-1-P], Erythrocytes) is the most sensitive index of dietary control. Increased concentrations of galactose may also be suggestive of severe hepatitis, biliary atresia of the newborn, and, in rare cases, galactose intolerance.


If results are outside the normal range and galactosemia is suspected, additional testing to identify the specific enzymatic defect is required. Results should be correlated with clinical presentation and confirmed by specific enzyme or molecular analysis. See Galactosemia Testing Algorithm in Special Instructions for follow-up of abnormal newborn screening results, comprehensive diagnostic testing, and carrier testing. See GALT / Galactose-1-Phosphate Uridyltransferase (GALT), Blood for GALT testing, GALK / Galactokinase, Blood for GALK testing, and GALE / UDP-Galactose-4 Epimerase (GALE), Blood for GALE testing.


No significant cautionary statements

Method Description

The formation of nicotinamide adenine dinucleotide (NADH) (reduced form) measured by the increase in absorbance at 340 nm is proportional to the amount of D-galactose in the sample.(Kurz G, Wallenfels K: Methods of Enzymatic Analysis. Vol. 3. Second edition. Edited by HV Bergmeyer. New York, Verlag Chemie, Weinheim, Academic Press, 1974, pp 1279-1282)

Analytic Time

8 days

Specimen Retention Time

1 month


1. Biochemical Genetics Patient Information (T602) in Special Instructions

2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.