Aspartic Acid Unit Converter
Aspartic Acid Unit Converter
Convert aspartic acid — aspartate — between mg/dL and µmol/L, with fasting reference intervals by age, and see why one laboratory publishes an upper limit only for an amino acid that plasma holds barely any of.
Aspartic Acid converter
mg/dL ⇄ µmol/LAspartic acid 0.040 mg/dL on a fasting plasma amino acid profile, separated promptly, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 75.1315
- 75.1315
- derived from the molecular weight of L-aspartic acid, 133.10 Da (C4H7NO4, PubChem CID 5960)
- asparagine is the amide
- 132.12 Da, a factor of 75.6888, within one per cent of this one. The adult intervals are not within one per cent: asparagine 23–94 µmol/L against an aspartate ceiling of about 7 to 13 µmol/L depending on the laboratory
- an upper limit only
- Mayo publishes aspartic acid as "less than 13" in adults rather than as a range, because plasma concentrations sit just above the floor and a low result carries no recognised meaning. Labcorp publishes both ends, which is why the groups on this page are Labcorp's
- the tube again
- red cells hold far more aspartate than plasma, so haemolysis and delayed separation raise it. Against a ceiling of a few µmol/L that matters more here than almost anywhere else on the profile
Worked example
Aspartic acid 0.040 mg/dL on a fasting plasma amino acid profile, separated promptly, read against the adult interval
0.040 × 75.1315 = 3.01 µmol/L, reported as 3.0 µmol/L
Within the Labcorp adult interval of 0.9–7.4 µmol/L used here, and comfortably under Mayo's adult upper limit of 13 µmol/L
Note how small the numbers are. A single-figure µmol/L result is why this page carries a decimal place: rounded to whole numbers, the adult interval would read 1–7 and the reader could not check the verdict
Converted with asparagine's factor by mistake, 0.040 mg/dL would read 3.0 µmol/L as well — the factors are within one per cent — but 3.0 µmol/L is an ordinary aspartate and far below any published asparagine interval. The abbreviation on the report, Asp or Asn, is what distinguishes them
Two published intervals, one of them an upper limit only
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | <13 (≥18 y) | <17 (2–17 y) | <48 (<24 months) |
| Labcorp — plasma amino acid intervals | 0.9 – 7.4 (>15 y) | 1.1 – 8.2 (2–15 y) | 1.6 – 13.4 (31 d–23 m); 1.8 – 32.3 (0–30 d) |
Aspartic acid and asparagine: the acid and the amide
| Analyte | MW (Da) | mg/dL → µmol/L | Adult interval (µmol/L) | What it tells you |
|---|---|---|---|---|
| Aspartic acid (Asp) | 133.10 | 75.1315 | 0.9 – 7.4 (Labcorp); under 13 (Mayo) | The acid, and scarce in plasma. Transaminated to and from oxaloacetate, used by asparagine synthetase to make asparagine, and released into the plasma by haemolysis or a slow separation. Rarely carries a diagnosis on its own |
| Asparagine (Asn) | 132.12 | 75.6888 | 23 – 94 (Mayo); 29.5 – 84.5 (Labcorp) | The amide, and about ten times more abundant. Depleted deliberately by asparaginase in acute lymphoblastic leukaemia, and low in about half of children with asparagine synthetase deficiency |
An amino acid plasma barely carries
Aspartic acid, usually called aspartate, sits at the junction of amino acid and carbohydrate metabolism: transaminated to and from oxaloacetate, donating nitrogen to the urea cycle through argininosuccinate, and combined with glutamine by asparagine synthetase to make asparagine. Its molecular weight is 133.10 Da, so 1 mg/dL is 75.13 µmol/L. Asparagine, the corresponding amide, is 132.12 Da and converts at 75.6888 — within one per cent, which makes the two factors effectively interchangeable and the two results emphatically not.
What sets this analyte apart on a plasma amino acid profile is how little of it there is. Published adult concentrations are single-figure µmol/L: Labcorp gives 0.9–7.4 µmol/L for anyone over 15, roughly a tenth of the asparagine on the same report and a twentieth of the glutamate. Mayo does not publish a range at all, only an upper limit — under 13 µmol/L in adults, under 17 for 2 to 17 years and under 48 under two years — because a low aspartate carries no recognised meaning and there is no useful floor to state. This page takes its reference groups from Labcorp for that reason, and tables Mayo’s ceilings beside them, which run about twice as high at every age.
Working at single figures makes the pre-analytical question unusually important. Red cells hold far more aspartate than plasma does, so haemolysis, a difficult sample or simply leaving the blood to stand before the plasma is taken off releases it — and against a ceiling of a few µmol/L, a small absolute release is a large proportional rise. The published handling advice for plasma amino acids is explicit: on ice immediately, or the plasma separated and frozen within thirty minutes. The direct measurements of this effect quantified glutamate rather than aspartate, so no figure is claimed here for aspartate specifically; the direction and the remedy are the same.
Clinically, aspartate is read as part of a pattern and almost never alone. It rises with glutamate when a sample has been mishandled, which is the commonest reason to see a high one. It is consumed on the other side of the reaction that asparaginase reverses, so a child on treatment for leukaemia has a depleted asparagine by design and the aspartate on the same report is of no separate importance. And where aspartate genuinely matters — urea cycle function, a suspected inherited disorder of amino acid metabolism — it matters as one line in a profile read by a metabolic service, beside the glutamate, the glutamine, the citrulline and the ammonia from the same fasting, promptly separated sample.
Frequently asked questions
How do I convert aspartic acid from mg/dL to µmol/L?
Multiply by 75.1315, derived from the molecular weight of aspartic acid, 133.10 Da. An aspartate of 0.040 mg/dL is 3.0 µmol/L. To go the other way, divide the µmol/L figure by 75.1315.
Why does my report give aspartic acid as "less than" a number?
Because Mayo publishes an upper limit only for this analyte — under 13 µmol/L in adults — rather than a range. Plasma concentrations sit close to the floor and a low result carries no recognised meaning, so there is no useful lower limit to state. Labcorp does publish both ends, 0.9–7.4 µmol/L for over-15s, and those are the reference groups used on this page.
Is aspartic acid the same as AST or aspartate aminotransferase?
No. AST is an enzyme measured in units per litre, and it happens to use aspartate as a substrate. Aspartic acid here is the amino acid itself, measured in µmol/L on a plasma amino acid profile. They are different tests with unrelated units.
Why is my aspartate high?
The sample is the first thing to check. Red cells contain far more aspartate than plasma, so haemolysis or a delay before separating the plasma releases it, and against an upper limit of a few µmol/L that shows up quickly. Blood for amino acids should go on ice immediately, or the plasma be separated and frozen within thirty minutes, and a raised result on a sample handled otherwise is worth repeating before it is interpreted.
Is aspartic acid the same as asparagine?
No. Asparagine is the amide of aspartic acid, 132.12 Da against 133.10, so the conversion factors are within one per cent — but asparagine circulates at about ten times the concentration, with an adult interval of 23–94 µmol/L. The abbreviations Asp and Asn are what distinguish them on a report.
Related calculators
References
- Davis JS, Darcy CJ, Piera K, et al. Ex-vivo changes in amino acid concentrations from blood stored at room temperature or on ice: implications for arginine and taurine measurements. BMC Clin Pathol. 2009;9:10.
- 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.