Proline Unit Converter
Proline Unit Converter
Convert proline between mg/dL and µmol/L, with fasting reference intervals by age — plus hyperprolinaemia types I and II, the vitamin B6 problem that type II creates, and why a haemolysed or slowly separated sample is the commonest reason a proline looks high.
Proline converter
mg/dL ⇄ µmol/LProline 2.00 mg/dL on a fasting plasma amino acid profile, read against the adult interval
Formula and conversion factor
mg/dL = µmol/L ÷ 86.8583
- 86.8583
- derived from the molecular weight of L-proline, 115.13 Da
- the sample first
- haemolysis, delayed separation and room-temperature transport all produce non-specific changes in a plasma amino acid profile, and most amino acids rise by more than 10% over 24 hours in whole blood — largely prevented by keeping the specimen on ice
- P5C inactivates vitamin B6
- in hyperprolinaemia type II, pyrroline-5-carboxylate accumulates and de-activates pyridoxal 5-phosphate, which may contribute to the seizures seen in that disorder and may be preventable with long-term vitamin B6 supplementation
- urine, not plasma height
- type I and type II are separated by the urinary organic acid pattern — type II excretes pyrroline-5-carboxylate — rather than by how high the plasma proline is
Worked example
Proline 2.00 mg/dL on a fasting plasma amino acid profile, read against the adult interval
2.00 × 86.8583 = 173.72 µmol/L, reported as 174 µmol/L
Within the Mayo adult interval of 107–383 µmol/L used here, and within Labcorp's 84.8–352.5 µmol/L
An order of magnitude below the concentrations reported in hyperprolinaemia type II, where a published case ran 2,290–2,955 µmol/L against a stated normal of 90–280
For a result that is above the interval, the first question is the specimen — haemolysed, or separated late? — and the second is the urine organic acids, which separate type I from type II. The plasma height does not
Two published intervals for fasting plasma proline
| Source | Adult (µmol/L) | Children (µmol/L) | Younger bands (µmol/L) |
|---|---|---|---|
| Mayo Clinic Laboratories — LC-MS/MS, fasting | 107 – 383 (≥18 y) | 99 – 389 (2–17 y) | 102 – 342 (<24 months) |
| Labcorp — plasma amino acid intervals | 84.8 – 352.5 (>15 y) | 84.5 – 365.0 (2–15 y) | 79.9 – 358.3 (31 d–23 m); 84.3 – 417.0 (0–30 d) |
A raised proline: the artefact, then the two disorders
| Consideration | What it looks like | What settles it |
|---|---|---|
| Haemolysed or slowly separated sample | A modest, non-specific rise, often across several amino acids at once. Most amino acids rise more than 10% in whole blood left 24 hours at room temperature, and the rise is largely prevented on ice | Repeat on a fasting specimen, separated promptly and kept cold. This is far commoner than either disorder below and is the first thing to exclude |
| Hyperprolinaemia type I | Raised plasma proline from proline oxidase (PRODH) deficiency, generally regarded as a benign biochemical finding | Urine organic acids, which do not show pyrroline-5-carboxylate, and a metabolic opinion. Not assumed to explain symptoms |
| Hyperprolinaemia type II | Higher concentrations — a published case ran 2,290–2,955 µmol/L against a normal of 90–280 — from P5C dehydrogenase (ALDH4A1) deficiency, and associated with seizures | Urinary pyrroline-5-carboxylate. P5C de-activates pyridoxal 5-phosphate, so vitamin B6 status is part of the assessment and long-term B6 supplementation may be protective |
| Urinary proline with hydroxyproline and glycine | Iminoglycinuria — the three share a renal transport system | A urine amino acid profile, not this plasma one. Iminoglycinuria is generally benign and is a transport variant rather than a metabolic disease |
Check the specimen, then look at the urine
Proline is a non-essential amino acid, unusual in being a secondary amine — its nitrogen sits inside a ring — which is why it and hydroxyproline are described as imino acids and why they share a renal transport system with glycine. Its molecular weight is 115.13 Da, so 1 mg/dL is 86.86 µmol/L. Mayo publishes 107–383 µmol/L for fasting adults and Labcorp 84.8–352.5 µmol/L over 15 years, with overlapping bands for younger ages; as always the interval that applies is the one printed on the report for that age.
The first thing to say about a raised proline is not a disorder but a specimen. Published intervals assume a fasting sample separated promptly, and non-specific changes arise from haemolysis, delayed separation or transport at room temperature: in whole blood left standing, most amino acid concentrations rise by more than 10% over 24 hours, and keeping the sample on ice largely prevents it. A modest rise in proline alongside modest rises elsewhere in the profile is much more likely to be a handling artefact than anything inherited, and the appropriate next step is a properly collected repeat.
Where the elevation is real and marked, there are two inherited hyperprolinaemias. Type I, from proline oxidase (PRODH) deficiency, is generally regarded as a benign biochemical finding. Type II, from pyrroline-5-carboxylate dehydrogenase (ALDH4A1) deficiency, produces higher concentrations — a published case ran 2,290–2,955 µmol/L against a stated normal of 90–280 — and is associated with seizures. The two are separated by the urinary organic acids rather than by the height of the plasma proline: type II accumulates pyrroline-5-carboxylate, and that metabolite de-activates pyridoxal 5-phosphate, the active form of vitamin B6. That is the mechanism proposed for the seizures in type II, and the reason long-term vitamin B6 supplementation has been suggested as protective.
Proline also appears in urine, with hydroxyproline and glycine, in iminoglycinuria — a benign renal transport variant read on a urine amino acid profile rather than this plasma one. None of these findings is made or excluded by a converted number. A raised plasma proline is a reason to check how the sample was taken and then to discuss the urine organic acids, the vitamin B6 question and the clinical picture with a metabolic service, which is where decisions about supplementation belong.
Frequently asked questions
How do I convert proline from mg/dL to µmol/L?
Multiply by 86.8583, derived from the molecular weight of proline, 115.13 Da. A proline of 2.00 mg/dL is 174 µmol/L. To go the other way, divide the µmol/L figure by 86.8583.
What is a normal proline level?
Mayo publishes 107–383 µmol/L for fasting adults and Labcorp 84.8–352.5 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 separated promptly.
Can a haemolysed sample raise the proline?
A haemolysed, slowly separated or warm sample produces non-specific changes across a plasma amino acid profile — most amino acids rise by more than 10% in whole blood left 24 hours at room temperature, largely prevented on ice. A modest isolated rise is much more likely to be that than a metabolic disorder, so the first step is a properly collected repeat.
What is the difference between hyperprolinaemia type I and type II?
Type I is proline oxidase (PRODH) deficiency and is generally regarded as benign. Type II is P5C dehydrogenase (ALDH4A1) deficiency, produces higher plasma concentrations and is associated with seizures. They are distinguished by the urinary organic acids — type II excretes pyrroline-5-carboxylate — not by how high the plasma proline is.
Why does hyperprolinaemia type II affect vitamin B6?
Because the pyrroline-5-carboxylate that accumulates in type II de-activates pyridoxal 5-phosphate, the active form of vitamin B6. That has been proposed as a contributor to the seizures in type II and as a reason long-term vitamin B6 supplementation may be protective — a question for a metabolic service, not something to start on the strength of a plasma proline.
Related calculators
References
- Farrant RD, Walker V, Mills GA, Mellor JM, Langley GJ. Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid: increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II. J Biol Chem. 2001;276(18):15107–15116.
- 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.