Asparagine Unit Converter
Asparagine Unit Converter
Convert asparagine between mg/dL and µmol/L, with fasting reference intervals by age — the amide partner of aspartic acid, deliberately emptied from plasma by asparaginase, and low in only about half of children with asparagine synthetase deficiency.
Asparagine converter
mg/dL ⇄ µmol/LAsparagine 0.70 mg/dL on a fasting plasma amino acid profile, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 75.6888
- 75.6888
- derived from the molecular weight of L-asparagine, 132.12 Da (C4H8N2O3, PubChem CID 6267)
- aspartic acid is the acid
- 133.10 Da, a factor of 75.1315. Asparagine is its amide — the same skeleton with an amide group in place of the second carboxyl — so the factors are within one per cent while the adult intervals are an order of magnitude apart, 23–94 against under 13
- ornithine, coincidentally
- 132.16 Da, a factor of 75.6659, which agrees with asparagine's to four significant figures. The two analytes have nothing to do with each other; the masses simply happen to match, and a shared factor is not a relationship
- asparaginase
- hydrolyses asparagine and empties the plasma pool deliberately. In a child on treatment, a depleted asparagine is the drug working and is read against the protocol, not against a reference interval
Worked example
Asparagine 0.70 mg/dL on a fasting plasma amino acid profile, read against the adult interval
0.70 × 75.6888 = 52.98 µmol/L, reported as 53 µmol/L
Within the Mayo adult interval of 23–94 µmol/L used here, and within Labcorp's 29.5–84.5 µmol/L
Converted with aspartic acid's factor by mistake, 0.70 mg/dL would read 53 µmol/L as well — the two factors are within one per cent — but 53 µmol/L is an ordinary asparagine and about four times the adult upper limit for aspartate. Check whether the report says Asn or Asp
And a result inside the interval does not settle the question that a low asparagine raises: in asparagine synthetase deficiency the plasma is low in only about half of affected individuals, and the cerebrospinal fluid is the sensitive sample
Two published intervals, in close agreement
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | 23 – 94 (≥18 y) | 25 – 80 (2–17 y) | 18 – 94 (<24 months) |
| Labcorp — plasma amino acid intervals | 29.5 – 84.5 (>15 y) | 31.6 – 100.5 (2–15 y) | 31.4 – 100.5 (31 d–23 m); 20.2 – 106.6 (0–30 d) |
Asparagine and aspartic acid: the amide and the acid
| Analyte | MW (Da) | mg/dL → µmol/L | Adult interval (Mayo, µmol/L) | What it tells you |
|---|---|---|---|---|
| Asparagine (Asn) | 132.12 | 75.6888 | 23 – 94 | The amide. Made by asparagine synthetase from aspartate and glutamine. Emptied deliberately by asparaginase in leukaemia, and low — in about half of cases — in asparagine synthetase deficiency, where the triad is congenital microcephaly, severe developmental delay and axial hypotonia with seizures in 82 per cent |
| Aspartic acid (Asp) | 133.10 | 75.1315 | under 13 | The acid. Present in plasma at a fraction of the asparagine concentration, and like glutamate it rises when a sample haemolyses or sits before separation. Mayo publishes an upper limit only, because there is no useful lower one |
The amide, the drug that removes it, and the sample that finds its absence
Asparagine is the amide of aspartic acid: the same four-carbon skeleton with an amide group in place of the second carboxyl. Its molecular weight is 132.12 Da, so 1 mg/dL is 75.69 µmol/L. Aspartic acid is 133.10 Da and converts at 75.1315, within one per cent, which means a conversion done with the wrong factor produces a plausible-looking number — while the adult reference intervals are an order of magnitude apart. Ornithine, at 132.16 Da, shares asparagine’s factor to four significant figures for no reason at all beyond coincidence of mass.
Reference intervals are age-dependent and laboratory-specific, and asparagine is one of the analytes where the two large published sets agree: Mayo gives 23–94 µmol/L for fasting adults and Labcorp 29.5–84.5 µmol/L for anyone over 15, with comparable bands for children. Both assume a fasting sample separated promptly, and the interval that applies is the one printed on your own report for that age.
Asparagine is unusual among amino acids in being the direct target of a drug. Asparaginase is a mainstay of treatment for acute lymphoblastic leukaemia, and depleting the circulating asparagine pool is not a side effect but the whole mechanism: leukaemic blasts express little or no asparagine synthetase, so once the plasma pool is emptied they cannot make their own, while normal cells can. A depleted asparagine in a child on treatment is therefore the expected result, interpreted against the treatment protocol rather than against any interval on this page.
The inherited counterpart is asparagine synthetase deficiency, a rare and severe disorder of biallelic ASNS variants presenting with congenital microcephaly, severe developmental delay and axial hypotonia that progresses to spastic quadriplegia, with seizures in 82 per cent. Here the honest limitation of a plasma converter has to be stated plainly: plasma asparagine is low in only about half of affected individuals, and it is not as sensitive as the cerebrospinal fluid concentration, which is typically low or not detected. A normal plasma asparagine does not exclude the diagnosis, and a low one does not make it — the diagnosis is established by identifying biallelic pathogenic ASNS variants, with the biochemistry supporting a clinical picture that is assessed by a metabolic service.
Frequently asked questions
How do I convert asparagine from mg/dL to µmol/L?
Multiply by 75.6888, derived from the molecular weight of asparagine, 132.12 Da. An asparagine of 0.70 mg/dL is 53 µmol/L. To go the other way, divide the µmol/L figure by 75.6888.
Is asparagine the same as aspartic acid?
No. Asparagine is the amide and aspartate the acid, differing by one amide group and less than one per cent of molecular weight — so their conversion factors are almost identical, 75.6888 against 75.1315. Their adult reference intervals are not: Mayo publishes 23–94 µmol/L for asparagine and an upper limit of 13 µmol/L for aspartic acid. Check whether the report says Asn or Asp.
What is a normal asparagine level?
Mayo publishes 23–94 µmol/L for fasting adults and Labcorp 29.5–84.5 µmol/L for anyone over 15, with different bands for children and infants. The two agree more closely than for most amino acids. Use the interval your own laboratory prints for that age, on a fasting sample separated promptly.
Why does asparaginase lower asparagine?
Because that is how the drug works. Asparaginase depletes the circulating asparagine pool, and leukaemic cells in acute lymphoblastic leukaemia make little or no asparagine synthetase, so they cannot replace what is removed while normal cells can. A depleted asparagine during treatment is the intended effect and is read against the protocol.
Does a normal plasma asparagine rule out asparagine synthetase deficiency?
No. Plasma asparagine is low in only about half of affected individuals and is less sensitive than the cerebrospinal fluid concentration, which is typically low or undetectable. The diagnosis is established by finding biallelic pathogenic variants in ASNS, in a child with congenital microcephaly, severe developmental delay and hypotonia.
Related calculators
References
- Alfadhel M, El-Hattab AW. Asparagine Synthetase Deficiency. In: GeneReviews. Seattle: University of Washington; 2018, updated 2025.
- Lomelino CL, Andring JT, McKenna R, Kilberg MS. Asparagine synthetase: function, structure, and role in disease. J Biol Chem. 2017;292(49):19952–19958.
- 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.