Unit Converter
Lysine (Lys)
(Essential Amino Acid – Key Marker in Inborn Errors of Metabolism, Nutritional Status & Aminoacidopathies)
Synonyms
- Lysine
- L-lysine
- Lys
- ε-amino-caproic acid (biochemical structure)
- Plasma lysine
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Molecular Weight
Lysine = 146.19 g/mol
Key Unit Conversions
1 mg/L = 6.84 µmol/L
1 mg/dL = 10 mg/L = 68.4 µmol/L
1 µmol/L = 0.146 mg/L
1 µg/mL = 1 mg/L
mg% = mg/dL
Description
Lysine is an essential, strictly dietary amino acid, required for:
- Protein synthesis
- Collagen formation
- Carnitine production
- Calcium absorption
- Growth and tissue repair
It plays a central role in pediatric growth, nitrogen balance, and metabolic homeostasis.
Lysine testing is performed as part of:
- Plasma Amino Acid Profile
- Evaluation of inborn errors of metabolism
- Nutritional assessment in children and critically ill patients
Physiological Role
1. Protein Synthesis
A major component of structural proteins (collagen, elastin).
2. Carnitine Biosynthesis
Lysine → precursor for carnitine (fatty-acid oxidation).
3. Collagen Cross-linking
Helps in bone growth, wound healing.
4. Growth & Muscle Mass
Essential in infants and children for linear growth.
5. Calcium Homeostasis
Facilitates intestinal calcium absorption and reduces renal excretion.
6. Immune Function
Needed for antibody production.
Clinical Significance
HIGH Lysine (Hyperlysinemia)
(Important in metabolic disorders)
1. Hyperlysinemia
Autosomal recessive deficiency of:
- Lysine-ketoglutarate reductase (LKR)
- Saccharopine dehydrogenase
Findings:
- Elevated plasma lysine
- Usually benign or mild symptoms
- Rarely developmental delay or seizures
- Considered a low toxicity aminoacidopathy
2. Pyridoxine-Dependent Epilepsy
High lysine & metabolites (e.g., α–AASA, P6C).
3. High Protein Intake
Excess supplementation or TPN.
4. Newborn Screening Abnormalities
Mild lysine elevation detected in some labs.
5. Liver Disease
Impaired amino acid metabolism.
LOW Lysine
More common clinically.
Causes
- Malnutrition
- Malabsorption (celiac, IBD)
- Severe burns, trauma
- Chronic liver disease
- Long-term TPN without adequate protein
- Cachexia / chronic illness
- Vegetarian/vegan diets without adequate legumes
Consequences
- Poor linear growth (children)
- Muscle wasting
- Poor wound healing
- Weakened immunity
- Hypocarnitinemia (fatigue, muscle weakness)
Reference Intervals
(Tietz 8E + Mayo + ARUP + ACMG)
Plasma Lysine
- Adults: 100 – 250 µmol/L
- Children: 100 – 270 µmol/L
- Infants: 120 – 300 µmol/L
- Newborns: 130 – 350 µmol/L
Abnormal Levels
- >300–400 µmol/L → hyperlysinemia or hepatic dysfunction
- <80 µmol/L → nutritional deficiency or malabsorption
Diagnostic Uses
1. Screen for Inborn Errors of Metabolism
- Hyperlysinemia
- Pyridoxine-dependent epilepsy
- Aminoacidopathies
- Organic acidemias (paired with metabolic acidosis)
2. Plasma Amino Acid Profile
Assessment in:
- Failure to thrive
- Seizures
- Developmental delay
- TPN monitoring
3. Nutritional Assessment
Especially in:
- Children
- Elderly
- Critical care patients
4. Liver Disease Evaluation
Altered lysine levels due to metabolic dysfunction.
5. Monitoring Treatment
Dietary therapy in metabolic diseases.
Analytical Notes
- Fasting sample recommended (significant post-prandial variation)
- Plasma (heparin) preferred; must be deproteinized promptly
- LC–MS/MS is gold standard
- Hemolysis affects amino acid patterns
- Interpret with other essential amino acids (threonine, arginine, leucine)
Clinical Pearls
- Isolated hyperlysinemia is usually benign, unlike MSUD.
- Lysine is vital for carnitine production - deficiency alters fatty-acid oxidation.
- Children with poor weight gain or recurrent infections often have low lysine.
- Lysine competes with arginine → used in preventing recurrent herpes simplex in some populations.
- In metabolic crises, lysine rises with other essential amino acids.
Interesting Fact
Lysine is often the first limiting amino acid in cereal-based diets (rice, wheat), making it essential in child nutrition programs in developing regions.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acids
- ACMG Guidelines - Amino Acid Disorders
- Mayo Clinic Laboratories - Plasma Amino Acids
- ARUP Consult - Metabolic Disorder Evaluation
- MedlinePlus / NIH - Amino Acid Tests