Galactose Classical

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No Fasting Required

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Newborn screening for galactose metabolism defect.

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Galactose Classical Test Information Guide

Why is it done?
- Test Purpose: Measures blood galactose levels to screen for galactosemia, a rare inherited metabolic disorder affecting the body's ability to process galactose (a simple sugar)
- Primary Indications: Newborn screening programs; suspected galactosemia due to developmental delay, cataracts, or hepatomegaly; family history of galactosemia; neonates with signs of sepsis-like illness or severe jaundice
- Typical Timing: Performed as part of routine newborn screening (2-5 days after birth); repeated testing if initial results are abnormal; screening for older children or adults with suggestive clinical features
Normal Range
- Reference Values: Normal galactose levels: Less than 20 mg/dL (1.1 mmol/L) in newborns and older children; some labs use <12 mg/dL as threshold
- Units of Measurement: mg/dL (milligrams per deciliter) or mmol/L (millimoles per liter)
- Interpretation: Normal (negative): Galactose within reference range indicates absence of galactosemia; Elevated (positive): Galactose above 20 mg/dL suggests possible galactosemia requiring confirmatory testing; Borderline: Results 12-20 mg/dL may warrant repeat testing or further investigation
- Clinical Significance: Normal results indicate normal galactose metabolism; abnormal results indicate possible classic galactosemia, galactokinase deficiency, or UDP-galactose-4-epimerase deficiency
Interpretation
- Elevated Galactose Levels (>20 mg/dL): Suggests impaired galactose metabolism; may indicate classic galactosemia (galactose-1-phosphate uridyltransferase deficiency), galactokinase deficiency, or UDP-galactose-4-epimerase deficiency
- Moderately Elevated Levels (20-40 mg/dL): May indicate milder forms of galactosemia or require confirmatory enzyme activity testing
- Significantly Elevated Levels (>40 mg/dL): Highly suggestive of classic galactosemia; urgent confirmatory testing and immediate dietary intervention required
- Factors Affecting Results: Timing of specimen collection (earlier detection may show higher levels); dietary galactose intake (milk, lactose-containing foods); hemolysis or improper sample handling; transfusions within 48 hours
- Clinical Correlation: Results must be interpreted with clinical signs (jaundice, hepatomegaly, developmental delay), enzyme activity assays (GALT activity), and second-tier testing for definitive diagnosis
Associated Organs
- Primary Organ Systems: Liver (primary site of galactose metabolism); eyes (lens); brain and nervous system; kidneys
- Conditions Associated with Abnormal Results: Classic galactosemia (galactose-1-phosphate uridyltransferase deficiency); galactokinase deficiency; UDP-galactose-4-epimerase deficiency (benign form); neonatal jaundice; hepatic dysfunction
- Diseases and Complications: Infantile cataracts (reversible if diet restricted early); intellectual disability and developmental delay; hepatomegaly and cirrhosis; ovarian failure in females; pseudotumor cerebri; renal tubular dysfunction
- Potential Complications: Accumulation of galactose-1-phosphate in tissues causing cellular damage; formation of galactitol in the lens leading to osmotic stress and cataract formation; toxic metabolite accumulation affecting neural function
Follow-up Tests
- Confirmatory Testing: Galactose-1-phosphate uridyltransferase (GALT) enzyme activity assay; quantitative total galactose measurement; galactose-1-phosphate levels; UDP-galactose-4-epimerase activity
- Secondary Investigations: Liver function tests (AST, ALT, bilirubin, albumin); ophthalmologic examination for cataracts; neuropsychological assessment; renal function tests; genetic testing for GALT, GALK1, or GALE gene mutations
- Monitoring Recommendations: Repeat galactose testing if initial screening is positive; repeat testing at 1-2 weeks after diagnosis; ongoing monitoring at clinic visits (every 3-6 months in first year, then annually); continuous assessment for long-term complications
- Related Complementary Tests: Tandem mass spectrometry (expanded newborn screening); galactitol measurement; newborn screening with other metabolic markers; plasma amino acid analysis
Fasting Required?
- Fasting Status: No - Fasting is NOT required for this test
- Special Instructions for Newborns: Test performed on newborn screening blood spot (dried blood spot from heel prick); should be collected 24-48 hours after birth (optimal timing); may be repeated at 7-10 days if initial results are borderline
- Dietary Considerations: Normal feeding should continue before testing; do NOT restrict milk or dairy products before screening as this may mask galactosemia; results may be affected if infant has received transfusion within 48 hours
- Patient Preparation: For newborns: Ensure proper heel warm-up before blood collection; collect adequate blood spot on filter paper; allow spot to air dry completely before transport; avoid contamination; for older children/adults: standard blood draw precautions apply; no special preparation needed
- Medications: No medications need to be avoided; inform healthcare provider if infant has received antibiotics or other medications as these do not typically affect galactose measurement

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