Isoleucine Unit Converter
Isoleucine Unit Converter
Convert isoleucine between mg/dL and µmol/L, with fasting reference intervals by age — and note that the factor is identical to leucine's, because the two are isomers of the same mass, while the analytes are not interchangeable at all.
Isoleucine converter
mg/dL ⇄ µmol/LIsoleucine 0.80 mg/dL on a fasting plasma amino acid profile, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 76.2369
- 76.2369
- derived from the molecular weight of L-isoleucine, 131.17 Da. Leucine has the same molecular weight and therefore the same factor — the two are isomers, identical in mass and different in everything clinical
- valine is different
- 117.15 Da and a factor of 85.3606. Using the isoleucine factor on a valine understates it by about 11 per cent, which is why the three branched-chain amino acids cannot share one conversion
- alloisoleucine
- an isomer again, so again 76.2369. Normally under 5 µmol/L, and the most sensitive and specific marker of maple syrup urine disease
- leucine is monitored
- in maple syrup urine disease leucine is the neurotoxic branched-chain amino acid and the analyte followed; isoleucine and valine are measured to make sure they have not fallen too low on the diet
Worked example
Isoleucine 0.80 mg/dL on a fasting plasma amino acid profile, read against the adult interval
0.80 × 76.2369 = 60.99 µmol/L, reported as 61 µmol/L
Within the Mayo adult interval of 29–153 µmol/L used here, and within Labcorp's 27.7–112.8 µmol/L
The same arithmetic would be correct for a leucine of 0.80 mg/dL, because leucine and isoleucine share a molecular weight of 131.17 Da — but it would be wrong for a valine, which converts at 85.3606
On a branched-chain profile this number means little alone. It is read beside the leucine, the valine and the alloisoleucine from the same fasting, promptly separated sample
Two published intervals, and how far apart their ceilings are
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | 29 – 153 (≥18 y) | 26 – 150 (2–17 y) | 23 – 149 (<24 months) |
| Labcorp — plasma amino acid intervals | 27.7 – 112.8 (>15 y) | 27.7 – 110.3 (2–15 y) | 25.2 – 126.4 (31 d–23 m); 19.3 – 127.4 (0–30 d) |
One factor, three amino acids, and only one of them monitored
| Amino acid | MW (Da) | mg/dL → µmol/L | Role in maple syrup urine disease |
|---|---|---|---|
| Leucine | 131.17 | 76.2369 | The neurotoxic one. Drives encephalopathy and cerebral oedema, and is the analyte monitored; maintenance target around 150–300 µmol/L |
| Isoleucine | 131.17 | 76.2369 — identical, an isomer of the same mass | Raised at diagnosis, far less neurotoxic, and supplemented on treatment. Too low an isoleucine causes a skin rash |
| Valine | 117.15 | 85.3606 — a different molecule, its own factor | Raised at diagnosis, also supplemented; kept at least twice the leucine, and continuous fortification is linked to long-term intellectual outcome |
| Alloisoleucine | 131.17 | 76.2369 | Normally under 5 µmol/L. Above that in the great majority of all forms of MSUD, and the diagnostic marker |
The same factor as leucine, and nothing else the same
Isoleucine is one of the three branched-chain amino acids, with leucine and valine, and it is essential — the body cannot make it. Its molecular weight is 131.17 Da, which gives a conversion factor of 76.2369 from mg/dL to µmol/L. That is exactly leucine’s factor, because leucine and isoleucine are isomers: the same atoms arranged differently, the same mass, and so the same arithmetic. Alloisoleucine, the diagnostic marker of maple syrup urine disease, is another isomer and converts identically. Valine is a smaller molecule at 117.15 Da and converts at 85.3606, so the three cannot share one factor.
Reference intervals are age-dependent and laboratory-specific, and for isoleucine the two largest published sets disagree at the top. Mayo publishes 29–153 µmol/L for fasting adults; Labcorp publishes 27.7–112.8 µmol/L for anyone over 15. The lower limits are close and the upper limits are 40 µmol/L apart, which is enough to change how a mildly raised result reads. Both are tabled above. The interval to use is the one on your own report, against a fasting sample separated promptly, because amino acids shift with feeding and drift in blood left standing before the plasma is taken off.
Clinically, isoleucine matters because of the company it keeps. All three branched-chain amino acids are raised in maple syrup urine disease, where the enzyme complex that decarboxylates their keto acids fails, but they are not managed the same way. Leucine is the neurotoxic one; leucine is what is monitored, and a rising leucine during an intercurrent illness is a metabolic emergency in the making. Isoleucine and valine are raised at diagnosis and then, on a branched-chain restricted diet, tend to fall too low — so both are supplemented rather than restricted further, and an isoleucine allowed to run low produces an acrodermatitis-like rash.
So a converted isoleucine is a small part of a bigger reading. On its own, a modest elevation much more often reflects how the sample was taken than anything inherited. Beside a raised leucine and valine, and an alloisoleucine above 5 µmol/L, it belongs to a pattern — and that pattern is confirmed and managed by a metabolic service, with the diet and the supplements set against serial measurements rather than any single number on any single day.
Frequently asked questions
How do I convert isoleucine from mg/dL to µmol/L?
Multiply by 76.2369, derived from the molecular weight of isoleucine, 131.17 Da. An isoleucine of 0.80 mg/dL is 61 µmol/L. To go the other way, divide the µmol/L figure by 76.2369.
Why is the isoleucine factor the same as leucine's?
Because leucine and isoleucine are isomers. They contain the same atoms in a different arrangement, so they share a molecular weight of 131.17 Da, and a mass-to-molar conversion depends only on the mass. Alloisoleucine is another isomer and converts identically. Valine is a different molecule, 117.15 Da, and converts at 85.3606.
What is a normal isoleucine level?
There is no single figure. Mayo publishes 29–153 µmol/L for fasting adults and Labcorp 27.7–112.8 µmol/L for anyone over 15, with different bands for children and infants. Use the interval your own laboratory prints for that age, on a fasting sample.
Is isoleucine monitored in maple syrup urine disease?
It is measured, but leucine is what is monitored for control and for decompensation, because leucine is the neurotoxic branched-chain amino acid. Isoleucine is checked mainly to make sure it has not fallen too low on the diet.
Why would isoleucine be supplemented rather than restricted?
Because a branched-chain restricted diet restricts all three, and isoleucine and valine tend to fall further than intended. A low isoleucine on treatment causes an acrodermatitis-like skin rash, so the metabolic service supplements it while keeping the leucine at target.
Related calculators
References
- Strauss KA, Carson VJ, Puffenberger EG. Maple Syrup Urine Disease. In: GeneReviews. Seattle: University of Washington; 2006, updated 2020.
- Frazier DM, Allgeier C, Homer C, et al. Nutrition management guideline for maple syrup urine disease: an evidence- and consensus-based approach. Mol Genet Metab. 2014;112(3):210–217.
- 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.