The GALT test measures galactose‑1‑phosphate uridyltransferase enzyme activity in red blood cells to diagnose classic galactosemia. Often done as newborn screening or from a heel‑prick/venous blood sample, low GALT activity indicates impaired galactose metabolism. Abnormal results lead to confirmatory biochemical and genetic testing. Early diagnosis allows urgent dietary management to prevent liver injury, sepsis, feeding issues, and developmental problems.

Many newborn screening (NBS) programs include testing for classic (GALT) galactosemia, but panels vary by country and state. A positive screen requires urgent confirmatory testing and prompt dietary treatment to prevent liver failure, sepsis, and developmental problems. Check your local NBS program or newborn screening authority to confirm whether galactosemia is included in your area.

GALT stands for galactose-1-phosphate uridylyltransferase. It is an enzyme in the Leloir pathway that converts galactose-1-phosphate to UDP-galactose. GALT deficiency causes classical galactosemia, leading to accumulation of galactose-1-phosphate and galactose, which can cause jaundice, liver dysfunction, hypoglycemia, cataracts, and increased risk of E. coli sepsis in newborns. Early diagnosis and dietary galactose restriction improve outcomes.

Changes in the GALT gene impair production of galactose-1-phosphate uridylyltransferase, blocking normal galactose metabolism. Pathogenic variants (nonsense, missense, deletions) reduce or abolish enzyme activity, causing accumulation of galactose-1-phosphate and other toxic metabolites that produce liver damage, jaundice, sepsis, cataracts, and developmental problems. Severe (classic) mutations cause near‑absent activity; Duarte variants retain partial activity.

Normal GALT (galactose‑1‑phosphate uridyltransferase) activity falls within the laboratory reference range — generally considered about 100% of expected activity. Labs report results as a percentage (100% normal) or in enzyme units (ranges vary by method). Very low activity (<1–10% of normal) indicates classic galactosemia; intermediate activity (~25–50%) suggests the Duarte variant. Interpret with lab-specific reference values.

GALT stands for Gut-Associated Lymphoid Tissue. It is the immune system component in the gastrointestinal tract — including Peyer’s patches, isolated lymphoid follicles, the appendix, tonsils, and lamina propria lymphocytes — that detects and defends against pathogens, promotes oral tolerance to food and commensal microbes, and coordinates mucosal immunity through antigen sampling, secretory IgA production, and cellular responses.