Serine Unit Converter
Serine Unit Converter
Convert serine between mg/dL and µmol/L, with fasting reference intervals by age — and why the CSF serine matters more than the plasma one, because in a serine biosynthesis defect a non-fasting plasma sample can be entirely normal.
Serine converter
mg/dL ⇄ µmol/LSerine 1.00 mg/dL on a fasting plasma amino acid profile, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 95.1565
- 95.1565
- derived from the molecular weight of L-serine, 105.09 Da. The same factor applies to a CSF serine, because it is the same molecule
- CSF serine
- very low in serine biosynthesis defects, usually under 13 µmol/L and in most individuals under 10. This is the measurement that carries the diagnosis, and it is why a lumbar puncture is part of the work-up
- fasting matters here
- fasting plasma serine is low in these disorders, but a non-fasting sample can be normal. The condition of the sample is part of the result
- not the glycine ratio
- in non-ketotic hyperglycinaemia it is the CSF to plasma glycine <i>ratio</i> that is diagnostic. For serine the two fluids are read against their own intervals, and the CSF concentration is the informative one
Worked example
Serine 1.00 mg/dL on a fasting plasma amino acid profile, read against the adult interval
1.00 × 95.1565 = 95.16 µmol/L, reported as 95 µmol/L
Within the Mayo adult interval of 55–146 µmol/L used here, and within Labcorp's 48.7–145.2 µmol/L
Two laboratories agreeing closely, for once — the serine intervals differ by only a few µmol/L at either end
If this sample was not fasting, the result is much weaker than it looks: in a serine biosynthesis defect the fasting plasma serine is low while a non-fasting one can be normal
And in a child with seizures, microcephaly or developmental delay, a normal plasma serine is not the end of the question. The CSF serine — usually under 13 µmol/L in these disorders — is what answers it
Two published intervals for fasting plasma serine
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | 55 – 146 (≥18 y) | 53 – 166 (2–17 y) | 59 – 224 (<24 months) |
| Labcorp — plasma amino acid intervals | 48.7 – 145.2 (>15 y) | 60.1 – 171.9 (2–15 y) | 65.4 – 205.6 (31 d–23 m); 60.6 – 236.2 (0–30 d) |
Serine and glycine: two disorders, two different measurements
| Serine biosynthesis defects | Non-ketotic hyperglycinaemia | |
|---|---|---|
| Genes | PHGDH (about 69% of cases), PSPH (25%), PSAT1 (6%) | GLDC, AMT — the glycine cleavage system |
| Plasma | Fasting serine low; a non-fasting sample can be normal. Fasting plasma glycine can be low to normal | Glycine raised, but the ranges in severe and attenuated disease overlap each other and the top of normal |
| CSF | Serine very low, usually under 13 µmol/L and in most individuals under 10. CSF glycine low to normal | Glycine raised, and read as the CSF to plasma ratio on simultaneous samples |
| Which measurement carries the diagnosis | The CSF serine concentration | The CSF to plasma glycine ratio, with CSF free of blood contamination |
| Treatment | Oral L-serine, typically started at 200–400 mg/kg/day and often needing 500–700 mg/kg/day in the young, with lower doses of 100–150 mg/kg/day in adolescents and adults; glycine is sometimes added | Supportive, with sodium benzoate and dextromethorphan in some protocols; no equivalent replacement therapy |
The plasma number is the weaker half of the measurement
Serine is a non-essential amino acid — the body makes it from a glycolytic intermediate through three enzymes — and it is central to one-carbon metabolism, to the synthesis of glycine, cysteine, phospholipids and nucleotides, and to the D-serine that modulates NMDA receptors in the brain. Its molecular weight is 105.09 Da, so 1 mg/dL is 95.16 µmol/L. The same factor converts a CSF serine, because it is the same molecule; the two fluids are simply read against their own intervals.
Serine matters more than most amino acids in this profile because of one group of disorders. If any of the three biosynthetic enzymes fails — PHGDH in about 69% of cases, PSPH in 25%, PSAT1 in 6% — the brain, which depends heavily on locally made serine, runs short. Infantile-onset disease presents with congenital or postnatal microcephaly, seizures and severe developmental delay; later-onset forms can present with seizures at school age or milder neurological disease. This is one of the few aminoacidopathies with a specific and effective treatment: oral L-serine, typically started at 200–400 mg/kg/day, often needing 500–700 mg/kg/day in the young and lower doses in adults, with glycine sometimes added.
Which is why the sample matters here more than anywhere else on this site. Published guidance is explicit that the fasting plasma serine is low in these disorders while a non-fasting sample can be normal — so a serine measured after a feed can miss a treatable diagnosis. And the plasma is the weaker measurement in any case. The CSF serine is very low, usually under 13 µmol/L and in most individuals under 10, and it is the CSF concentration that carries the diagnosis. That is a different arrangement from glycine, where non-ketotic hyperglycinaemia is confirmed on the CSF to plasma glycine ratio taken on simultaneous samples rather than on either concentration alone.
So read a converted plasma serine for what it is: a screening value, only as good as the fast and the separation behind it, and interpreted against an interval for that age. A low fasting serine in a child with seizures or microcephaly is a reason to involve a metabolic service quickly, because the treatment exists and the confirmatory test is a CSF measurement rather than a repeat of this one. A normal result in the same child is not an answer.
Frequently asked questions
How do I convert serine from mg/dL to µmol/L?
Multiply by 95.1565, derived from the molecular weight of serine, 105.09 Da. A serine of 1.00 mg/dL is 95 µmol/L. To go the other way, divide the µmol/L figure by 95.1565. The same factor converts a CSF serine.
What is a normal serine level?
Mayo publishes 55–146 µmol/L for fasting adults and Labcorp 48.7–145.2 µmol/L over 15 years — unusually close agreement. Values are higher in younger children, up to 224 µmol/L under two years at Mayo, and higher again in the first months of life. Use the interval your own report prints for that age.
Why does the CSF serine matter more than the plasma serine?
Because it is the measurement that carries the diagnosis. In serine biosynthesis defects the CSF serine is very low, usually under 13 µmol/L and in most individuals under 10, while the plasma serine is low only when the sample is taken fasting and can be normal otherwise.
Can a normal plasma serine exclude a serine biosynthesis defect?
No. Published guidance states that fasting plasma serine is low in these disorders but non-fasting samples can be normal. Where a child has seizures, microcephaly or unexplained developmental delay, a normal plasma serine does not close the question — a CSF serine, arranged through a metabolic service, is what does.
How does this differ from glycine in non-ketotic hyperglycinaemia?
Both are investigated in CSF, but with different measurements. For serine it is the absolute CSF concentration. For glycine it is the ratio of CSF to plasma glycine on simultaneous samples, with CSF free of blood contamination, because the plasma glycine ranges in severe and attenuated disease overlap.
Is a raised serine significant?
Rarely on its own. Diet, a non-fasting sample and delayed separation account for most modest elevations, and valproate is associated with raised glycine, alanine and serine in treated children. The disorders that make serine worth measuring produce low values, not high ones.
Related calculators
References
- van der Crabben SN, de Koning TJ. Serine Deficiency Disorders. In: GeneReviews. Seattle: University of Washington; 2023.
- Mayo Clinic Laboratories. Test ID: AAQP — Amino Acids, Quantitative, Plasma. Liquid chromatography tandem mass spectrometry. Reference values are for fasting patients, in three age bands (under 24 months, 2–17 years, 18 years and over). Accessed 2026.
- Labcorp. Plasma Amino Acid Reference Intervals — four age bands from 0–30 days to over 15 years, µmol/L. Accessed 2026.
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.