Galactose Unit Converter
Galactose Unit Converter
Convert galactose between mg/dL and mmol/L — the same factor as glucose, because the two share a molecular mass — with the newborn screening cut-offs and why an abnormal screen is acted on before it is confirmed.
Galactose converter
mg/dL ⇄ mmol/LTotal galactose 12 mg/dL on a newborn screening spot, read against the lowest cut-off in use
Formula and conversion factor
mg/dL = mmol/L ÷ 0.0555062
- 0.0555062
- derived from the molecular weight of D-galactose, 180.16 Da. Galactose is an epimer of glucose with the same formula, C₆H₁₂O₆, so the familiar glucose factor of 0.0555 converts galactose unchanged
- total galactose
- newborn screening usually reports total galactose — free galactose plus galactose-1-phosphate — on a dried blood spot, or measures GALT enzyme activity, or both, depending on the programme
- the check that confirms it
- GeneReviews gives plasma free galactose in classical galactosaemia as 90–360 mg/dL, or 5–20 mmol/L. 90 × 0.0555062 is 5.00, which is the factor reproducing published paired units exactly
- a screen, not a diagnosis
- most positive galactosaemia screens are the benign Duarte variant or false positives. GALT activity and erythrocyte galactose-1-phosphate are what confirm it
Worked example
Total galactose 12 mg/dL on a newborn screening spot, read against the lowest cut-off in use
12 × 0.0555062 = 0.67 mmol/L, which is 666 µmol/L
Above the 5 mg/dL cut-off used by the most conservative programmes, and above the 8–10 mg/dL a healthy milk-fed newborn typically carries — but below the 20 mg/dL that other programmes use
That spread is the point: the same 12 mg/dL is a positive screen in one country and a negative one in another
It is not a diagnosis in either. GALT enzyme activity and erythrocyte galactose-1-phosphate decide that
And in a neonate who is jaundiced, vomiting or unwell, lactose stops now and the confirmatory tests follow — waiting for them is the harm
The numbers used in newborn screening
| mg/dL | mmol/L | µmol/L | |
|---|---|---|---|
| Range of total galactose cut-offs across screening programmes | 5 – 20 | 0.28 – 1.11 | 278 – 1,111 |
| Typical total galactose in a healthy milk-fed newborn | 8 – 10 | 0.44 – 0.56 | 444 – 556 |
| Erythrocyte galactose-1-phosphate, normal infant | < 1 | < 0.06 | < 38 |
| Erythrocyte galactose-1-phosphate, classical galactosaemia, newborn period | usually > 10, up to 120 | > 0.56 | > 556 |
| Plasma free galactose, classical galactosaemia | 90 – 360 | 5 – 20 | — |
Why the result is acted on before it is confirmed
| What happens | Timing | |
|---|---|---|
| An affected infant starts milk | Galactose-1-phosphate accumulates and is directly toxic to liver, kidney and brain | Jaundice, vomiting, poor feeding, hepatomegaly, bleeding and E. coli sepsis within days |
| Lactose is stopped | The toxic metabolite stops accumulating. A soy-based or elemental formula replaces milk | Immediately, on the screening result, in an unwell infant — before confirmation |
| Confirmatory testing | GALT enzyme activity and erythrocyte galactose-1-phosphate, with genotyping | Runs in parallel, not before |
| Most positive screens | Duarte variant, or a plain false positive — no overt disease | Feeding is resumed once GALT activity is known |
A number that is acted on, not waited on
Galactose is the sugar released with glucose when lactose is digested, and it is an epimer of glucose with the same molecular formula and the same molecular mass of 180.16 Da. That has a genuinely useful consequence: the familiar glucose conversion factor of 0.0555 converts galactose unchanged, so 12 mg/dL of either is 0.67 mmol/L. It is one of the few places in clinical biochemistry where a factor can be safely reused for a different analyte, and the reason is structural rather than coincidental.
The clinical context is classical galactosaemia, caused by deficiency of galactose-1-phosphate uridyltransferase. Newborn screening programmes measure total galactose on a dried blood spot, or GALT enzyme activity, or both, depending on the programme. Cut-offs for total galactose vary from about 5 to 20 mg/dL between programmes — a fourfold spread — because each is set against its own assay and its own tolerance for false positives. A healthy milk-fed newborn typically carries 8 to 10 mg/dL, so the same measured value can be a positive screen in one country and a negative one in another.
A raised total galactose is not itself diagnostic. Most positive screens turn out to be the benign Duarte biochemical variant or straightforward false positives, and the diagnosis is made on GALT enzyme activity and erythrocyte galactose-1-phosphate rather than on the screening analyte. Equally, a total galactose below the cut-off does not exclude the condition: an infant who has not yet been fed milk has not had the substrate to accumulate, and a screening result should never be used to reassure about a neonate who is actually unwell.
What makes galactosaemia different from most screening conditions is the speed. An affected infant who is drinking milk accumulates galactose-1-phosphate, which is directly toxic to liver, kidney and brain, and deteriorates within days of the first feed — jaundice, vomiting, poor feeding, hepatomegaly, bleeding and a characteristic vulnerability to Escherichia coli sepsis. So the abnormal result is acted on rather than confirmed first: lactose is stopped immediately in an infant who is unwell, and the confirmatory tests run alongside that rather than before it. Stopping milk for a few days in a baby who turns out to be unaffected costs very little. Waiting in one who is affected can cost everything, and that judgement belongs to a metabolic service contacted the same day.
Frequently asked questions
How do I convert galactose from mg/dL to mmol/L?
Multiply by 0.0555062, derived from the molecular weight of galactose, 180.16 Da. So 12 mg/dL is 0.67 mmol/L. Because galactose and glucose are isomers with the same molecular mass, the familiar glucose factor of 0.0555 works for galactose unchanged.
Is galactose converted with the same factor as glucose?
Yes. Galactose is an epimer of glucose — the same formula, C₆H₁₂O₆, and the same molecular mass of 180.16 Da — so the mg/dL to mmol/L factor is identical at 0.0555. This is one of the few analyte pairs where reusing a conversion factor is genuinely safe.
What total galactose is used as a newborn screening cut-off?
It varies between programmes, from about 5 to 20 mg/dL (278–1,111 µmol/L), because each cut-off is set against a particular assay and a particular tolerance for false positives. A healthy milk-fed newborn typically carries 8 to 10 mg/dL.
Does a raised total galactose mean galactosaemia?
No. Most positive screens are the benign Duarte variant or false positives. The diagnosis is made on galactose-1-phosphate uridyltransferase activity and erythrocyte galactose-1-phosphate, not on total galactose. But a raised result in an unwell neonate is treated as urgent while those tests are run.
Can a normal total galactose exclude galactosaemia?
Not reliably. An infant who has not yet been fed milk has had no substrate to accumulate, so the total galactose can be unremarkable. In a neonate who is jaundiced, vomiting, feeding poorly or septic, GALT activity should be measured regardless of what the screening galactose showed.
Related calculators
References
- Berry GT. Classic Galactosemia and Clinical Variant Galactosemia. In: GeneReviews. Seattle: University of Washington; 2000, updated 2021.
- Welling L, Bernstein LE, Berry GT, et al. International clinical guideline for the management of classical galactosemia: diagnosis, treatment, and follow-up. J Inherit Metab Dis. 2017;40(2):171–176.
- Pyhtila BM, Shaw KA, Neumann SE, Fridovich-Keil JL. Newborn screening for galactosemia in the United States: looking back, looking around, and looking ahead. JIMD Rep. 2015;15:79–93.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.