Unit Converter
Arginine (Arg)
(L-Arginine – Essential Nitric Oxide Precursor & Urea Cycle Amino Acid)
Synonyms
- Arginine
- L-Arginine
- Arg
- 2-Amino-5-guanidinovaleric acid
- Proteinogenic amino acid
Units of Measurement
µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL
Description
Arginine is a semi-essential amino acid involved in:
- Protein synthesis
- Urea cycle (detoxification of ammonia)
- Nitric oxide (NO) production
- Hormone secretion (GH, insulin, glucagon)
- Immune function
Arginine levels in plasma are measured as part of amino acid profiling to diagnose:
- Urea cycle disorders
- Nitric oxide pathway abnormalities
- Nutritional deficiencies
- Metabolic or mitochondrial diseases
Physiological Role
1. Urea Cycle Function
Arginine is a precursor for urea and essential in detoxifying ammonia.
Levels rise in urea cycle defects, especially arginosuccinate lyase deficiency.
2. Nitric Oxide (NO) Synthesis
Arginine is the substrate for NO synthase → nitric oxide → vasodilation, endothelial health.
3. Creatine & Polyamine Synthesis
Required for:
- Creatine
- Agmatine
- Ornithine → Proline (collagen)
4. Immune Function
Enhances T-cell function and wound healing.
Clinical Significance
Elevated Arginine
1. Urea Cycle Disorders (UCD)
Especially:
- Arginase deficiency (ARG1 deficiency) → very high arginine
- ASS deficiency (Citrullinemia)
- ASL deficiency
2. Liver Disease
Impaired urea synthesis → mild increases.
3. Renal Failure
Reduced clearance.
4. High-Protein Intake / TPN
Low Arginine
Seen in:
- Severe malnutrition
- Critical illness
- Sepsis
- Trauma/burns
- Mitochondrial disorders
- Neonatal hyperammonemia from other causes
- Severe hemolysis or hepatic failure (used rapidly)
Reference Intervals
(Tietz 8E + Mayo Clinic Amino Acid Panel + IFCC)
Plasma Arginine
- 40 – 120 µmol/L (fasting adults)
- ≈ 7 – 21 mg/L
Children
- Slightly higher in infants & children due to growth
Arginase Deficiency
- Often > 300–500 µmol/L
Unit Meanings
| Unit | Meaning |
| µmol/L | micromole per liter |
| mg/L | milligram per liter |
| mg/dL | milligram per deciliter |
| mg/100 mL | mg% |
| mg% | milligram per 100 mL |
| µg/mL | microgram per milliliter |
Diagnostic Uses
1. Urea Cycle Disorder Screening
Pattern recognition:
- High arginine → arginase deficiency
- High citrulline + altered arginine → ASS/ASL defects
- Hyperammonemia + abnormal amino acids → UCD diagnosis
2. Metabolic Illness Evaluation
- Inborn errors of metabolism
- Organic acidemias
- Fatty acid oxidation defects
3. Nutritional Assessment
Levels fall in:
- Malnutrition
- Critical care patients
- Neonates with poor intake
4. Cardiovascular Research
Used to assess:
- Endothelial NO production
- Arginine/ADMA ratio (vascular risk marker)
Analytical Notes
- Method: LC-MS/MS or HPLC
- Fasting sample preferred
- Avoid hemolysis (RBCs high in arginine)
- Plasma separated immediately
- Store frozen if delayed
Clinical Pearls
- Extremely high arginine → think arginase deficiency.
- Arginine is not cycle-dependent; stable fasting analyte.
- High arginine + high ammonia = UCD until proven otherwise.
- In critical illness, low arginine correlates with poor NO production and immune dysfunction.
- Arginine supplementation is contraindicated in arginase deficiency (worsens hyperargininemia).
Interesting Fact
Arginine was first discovered in 1886 from lupin seedlings, and later identified as the major substrate for nitric oxide, revolutionizing cardiovascular physiology.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Amino Acids.
- Mayo Clinic Laboratories - Plasma Amino Acid Panel.
- ARUP Consult - Urea Cycle Disorder Interpretation.
- IFCC Reference Methods for Amino Acid Measurement.
- NIH / MedlinePlus - Arginine Overview.
- Genetics in Medicine - Urea Cycle Disorders.
- Metabolic Disease Texts - Hyperargininemia.