Unit Converter
Galactose
(Monosaccharide – Key Marker for Galactosemia, Liver Dysfunction & Metabolic Disorders)
Synonyms
- Galactose
- Blood galactose
- Plasma galactose
- Reducing sugar
- Seminal galactose (rare, not clinically significant)
Units of Measurement
- mmol/L
- µmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
Unit Conversions
(Molecular Weight = 180.16 g/mol - same as glucose/fructose)
1 mg/dL = 0.0555 mmol/L
1 mg/L = 0.00555 mmol/L
1 µg/mL = 1 mg/L
mg/dL = mg% = mg/100 mL
1 mmol/L = 1000 µmol/L
Description
Galactose is a simple carbohydrate (monosaccharide) derived from:
- Lactose breakdown (milk sugar → glucose + galactose)
- Dietary intake
- Endogenous metabolism
Clinically, galactose testing is most important in newborns, as elevated levels indicate galactosemia, a potentially life-threatening metabolic disorder.
Physiological Role
- Component of lactose metabolism in infants
- Important for cellular glycoprotein and glycolipid synthesis
- Converted to glucose via the Leloir pathway
- Galactokinase (GALK)
- Galactose-1-phosphate uridyltransferase (GALT)
- UDP-galactose epimerase (GALE)
- Galactokinase (GALK)
Any enzyme block leads to galactose accumulation → toxicity.
Clinical Significance
1. Newborn Screening (Most Important Application)
Galactose is routinely screened in newborns to detect galactosemia, a critical metabolic condition.
Types of Galactosemia
- Classic galactosemia (GALT deficiency)
- Most severe
- Life-threatening
- Most severe
- Galactokinase deficiency (GALK)
- Cataracts
- Cataracts
- GALE deficiency
- Variable severity
- Variable severity
Galactose accumulates causing:
- Liver damage
- Jaundice
- Vomiting
- Hypoglycemia
- Lethargy
- Sepsis (E. coli)
- Cataracts
- Brain injury
Immediate lactose restriction is lifesaving.
2. Liver Disease
High blood galactose due to:
- Impaired hepatic metabolism
- Cirrhosis
- Neonatal cholestasis
- Liver failure
3. Inborn Errors of Metabolism in Adults
Rare but include:
- Partial GALT deficiency
- Epimerase deficiencies
- Transport defects
4. Dietary or Malabsorption Issues
Postprandial galactose elevation may occur after high lactose ingestion.
Reference Intervals
1. Blood Galactose in Newborns
| Status | Galactose Level (mg/dL) | mmol/L |
| Normal | < 5 mg/dL | <0.28 mmol/L |
| Borderline | 5–10 mg/dL | 0.28–0.55 mmol/L |
| Suggestive of galactosemia | >10 mg/dL | >0.55 mmol/L |
| High risk / diagnostic | >20 mg/dL | >1.11 mmol/L |
2. Adults
Fasting galactose levels are usually:
- <3 mg/dL (≈ <0.17 mmol/L)
Diagnostic Uses
1. Galactosemia Diagnosis (Primary Use)
High blood galactose → evaluate:
- GALT enzyme activity
- RBC galactose-1-phosphate
- Genetic testing (GALT mutations)
2. Monitoring Diet in Galactosemia
Ensure strict lactose/galactose restriction.
3. Liver Function Assessment
High galactose may reflect:
- Hepatic metabolic failure
- Reduced galactose clearance
4. Newborn Jaundice Evaluation
Differentiates:
- Metabolic causes
- Cholestasis
- Breastfeeding-related jaundice
Analytical Notes
- Blood sample (often dried blood spot for newborn screening)
- Enzymatic assays for galactose & galactose-1-phosphate
- Avoid hemolysis—may affect enzyme studies
- Genetic testing confirms diagnosis
Clinical Pearls
- Classic galactosemia is a medical emergency—treat immediately, even before confirmatory tests.
- Cataracts in infants may be a clue to GALK deficiency due to galactitol accumulation.
- High galactose with normal GALT → check for GALE deficiency or liver disease.
- Breast milk contains lactose → must be avoided in classic galactosemia.
- Early treatment dramatically improves survival but does not prevent all long-term complications.
Interesting Fact
Galactose is a component of human milk oligosaccharides, essential for brain development - highlighting why galactosemia is so harmful in newborns.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Carbohydrate Disorders.
- ACMG Guidelines - Newborn Screening for Galactosemia.
- CDC/WHO Newborn Screening Standards.
- Mayo Clinic Laboratories - Galactose & GALT.
- ARUP Consult - Galactosemia Workup.
- MedlinePlus / NIH - Galactose Test.