Lysine Unit Converter
Lysine Unit Converter
Convert lysine between mg/dL and µmol/L, with fasting reference intervals by age — and why a low or even normal plasma lysine can be the more important result, because lysinuric protein intolerance presents with hyperammonaemia after protein.
Lysine converter
mg/dL ⇄ µmol/LLysine 2.50 mg/dL on a fasting plasma amino acid profile, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 68.4041
- 68.4041
- derived from the molecular weight of L-lysine, 146.19 Da. Lysine is one of the larger amino acids, so its factor is one of the smaller ones
- read with arginine and ornithine
- the three dibasic amino acids share the y+L transporter. A transport defect lowers all three in plasma and raises all three in urine, which is why one of them alone is a weak signal
- the urine, not the plasma
- in lysinuric protein intolerance it is the 24-hour urinary excretion of cationic amino acids, especially lysine, that is increased — plasma values are usually low but may be normal
- ammonia after protein
- plasma ammonia rises after a protein-rich meal in lysinuric protein intolerance while the fasting value is usually normal, so a normal fasting ammonia does not exclude it
Worked example
Lysine 2.50 mg/dL on a fasting plasma amino acid profile, read against the adult interval
2.50 × 68.4041 = 171.01 µmol/L, reported as 171 µmol/L
Within the Mayo adult interval of 105–335 µmol/L used here, and within Labcorp's 94.0–278.0 µmol/L
Well below the 600–2,000 µmol/L reported in hyperlysinaemia, so that is not the question this result raises
And not reassuring about the other direction on its own: cationic amino acids in lysinuric protein intolerance may be within the normal range, so if the history fits, the urine amino acids and an ammonia measured after protein are the tests that matter
Two published intervals, and a paediatric lower limit worth noticing
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | 105 – 335 (≥18 y) | 61 – 291 (2–17 y) | 83 – 304 (<24 months) |
| Labcorp — plasma amino acid intervals | 94.0 – 278.0 (>15 y) | 82.7 – 239.5 (2–15 y) | 70.4 – 279.2 (31 d–23 m); 83.2 – 334.2 (0–30 d) |
Lysine in two directions, and what actually settles each
| Direction | Pattern | What carries the diagnosis |
|---|---|---|
| Low, with low arginine and ornithine | Lysinuric protein intolerance — SLC7A7, the y+LAT-1 transporter. Protein aversion, vomiting after protein, failure to thrive, later interstitial lung disease, haemophagocytosis, osteoporosis and renal involvement | Increased 24-hour urinary excretion of cationic amino acids, especially lysine, with hyperammonaemia after a protein-rich meal. Plasma values are usually low but may be normal, and the fasting ammonia usually is normal. Long-term management includes protein restriction and citrulline up to 100 mg/kg/day in four doses with meals |
| Very high in isolation | Hyperlysinaemia — AASS deficiency. Reported plasma lysine 600–2,000 µmol/L | Largely benign. About half of reported individuals are asymptomatic and pathogenicity remains debated, so it is not assumed to explain a child’s symptoms without a metabolic opinion |
| Mildly high | Diet, a lysine supplement, a non-fasting sample, or delayed separation | Repeating properly, fasting and promptly separated, before anything else |
| Low in isolation, no other pattern | Low protein intake, prolonged fasting, a dilute profile | The rest of the profile, read as a whole |
Lysine is read with arginine and ornithine, and often with the urine
Lysine is an essential amino acid and one of the three dibasic, or cationic, amino acids, with arginine and ornithine. Its molecular weight is 146.19 Da, so 1 mg/dL is 68.40 µmol/L. The three share a transport system in the kidney and gut — y+L — and that shared transport is what makes a lysine worth reading beside the other two rather than alone.
Reference intervals are age-dependent and laboratory-specific, and for lysine they diverge in an awkward place. Mayo publishes 105–335 µmol/L for fasting adults and 61–291 µmol/L for 2 to 17 years; Labcorp publishes 94.0–278.0 µmol/L over 15 years and 82.7–239.5 µmol/L for 2 to 15 years. A lysine of 70 µmol/L in a ten-year-old is inside one published paediatric interval and below the other. Both sets assume a fasting sample separated promptly, and the interval that applies is the one on your own report for that age.
The raised direction is usually the less important one. Hyperlysinaemia, from a defect in the AASS gene, produces plasma concentrations reported at 600–2,000 µmol/L and is largely benign: around half of reported individuals are asymptomatic, and whether the biochemistry itself causes harm is still debated. A mildly raised lysine is much more often diet, a supplement, or a sample handled slowly. The low direction is where a diagnosis lives. In lysinuric protein intolerance the dibasic amino acids leak into the urine, plasma lysine, arginine and ornithine are usually below normal for age — though they may sit inside the interval — and the presentation is hyperammonaemia after protein, with vomiting, protein aversion and failure to thrive, in a child whose fasting ammonia is normal.
That combination is the honest limitation of this page. A converted plasma lysine cannot confirm or exclude lysinuric protein intolerance; the increased urinary excretion of cationic amino acids and an ammonia measured after a protein load are what do. If that is the question, it belongs with a metabolic service, which will also set treatment — protein restriction with citrulline supplementation — against the whole picture rather than any single result.
Frequently asked questions
How do I convert lysine from mg/dL to µmol/L?
Multiply by 68.4041, derived from the molecular weight of lysine, 146.19 Da. A lysine of 2.50 mg/dL is 171 µmol/L. To go the other way, divide the µmol/L figure by 68.4041.
What is a normal lysine level?
There is no single figure. Mayo publishes 105–335 µmol/L for fasting adults and Labcorp 94.0–278.0 µmol/L for anyone over 15, with different and materially different bands for children. Use the interval your own laboratory prints for that age, on a fasting sample separated promptly.
What does a low plasma lysine mean?
Most often low protein intake, prolonged fasting or a generally dilute profile. The specific cause to consider is lysinuric protein intolerance, where lysine, arginine and ornithine are lost in the urine; there the diagnosis rests on heavy urinary excretion of cationic amino acids and hyperammonaemia after protein, not on the plasma level, which may even be normal.
Is a high lysine dangerous?
Markedly raised lysine raises hyperlysinaemia, which is largely benign — about half of reported individuals are asymptomatic and its pathogenicity is debated. It is not assumed to explain symptoms without a metabolic opinion, and a mild elevation is more often dietary or pre-analytical.
Why is a normal fasting ammonia not reassuring in lysinuric protein intolerance?
Because the hyperammonaemia is post-prandial. Plasma ammonia rises after a protein-rich meal while the fasting value is usually normal, so a normal fasting ammonia does not exclude the diagnosis in a child who avoids or vomits protein.
Related calculators
References
- Nunes V, Niinikoski H. Lysinuric Protein Intolerance. In: GeneReviews. Seattle: University of Washington; 2006, updated 2018.
- Marinella G, Pascarella F, Vetro A, et al. Hyperlysinemia, an ultrarare inborn error of metabolism: review and update. Seizure. 2024;120:135–141.
- 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.