Unit Converter
Threonine (Thr)
(Essential Amino Acid - Important in Protein Synthesis, Intestinal Integrity & Inborn Metabolic Disorders)
Synonyms
- Threonine
- L-Threonine
- Thr
- 2-Amino-3-hydroxybutyric acid
- Essential hydroxyl amino acid
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Unit Conversions
Molecular Weight of Threonine = 119.12 g/mol
µmol/L ↔ mg/L
1 µmol/L=0.119 mg/L1\ \text{µmol/L} = 0.119\ \text{mg/L}1 µmol/L=0.119 mg/L 1 mg/L=8.40 µmol/L1\ \text{mg/L} = 8.40\ \text{µmol/L}1 mg/L=8.40 µmol/L
mg/dL → mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
mg% = mg/dL
µg/mL ↔ mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
Description
Threonine is an essential amino acid, meaning it must be obtained through diet.
It plays major roles in:
- Protein synthesis
- Immune function
- Intestinal mucin production (key for gut integrity)
- One-carbon metabolism
- Glycine and serine synthesis
- Central nervous system development
Threonine is measured in plasma amino-acid panels to investigate inborn errors of metabolism, nutritional status, and liver disease.
Physiological Role
1. Intestinal Health
Threonine is a major component of:
- Mucins
- Glycoproteins
- Immune IgA production
2. Protein & Collagen Synthesis
Required for structural proteins and tissue repair.
3. One-Carbon Metabolism
Threonine contributes carbons to:
- Glycine
- Serine
- Metabolic intermediates
4. CNS Development
Important for brain maturation in newborns.
5. Immune Function
Supports antibody production and cytokine regulation.
Clinical Significance
HIGH THREONINE
1. Inborn Errors of Metabolism
Most clinically important cause.
- Threonine dehydratase deficiency
- Glycine cleavage system defects
- Mitochondrial disorders
- Propionic acidemia & methylmalonic acidemia (secondary elevation)
- Phenylketonuria (PKU) – mild ↑
- Maple syrup urine disease (MSUD) – moderate ↑ along with branched-chain AAs
2. Immature Liver Function
Transient elevation common.
3. Liver Disease
Portal hypertension, cirrhosis.
4. Parenteral Nutrition
High amino-acid infusion.
5. Catabolic Stress
Sepsis, trauma → altered amino-acid profile.
LOW THREONINE
Causes
- Malnutrition
- Malabsorption
- Chronic illness
- Severe liver disease
- Increased threonine catabolism
- Inflammatory bowel disease
- Low-protein diets
- Some mitochondrial disorders
Symptoms
Often non-specific:
- Poor growth
- Muscle wasting
- Low albumin
- Fatigue
- Poor immune response
Reference Intervals
(Tietz 8E + Mayo + ARUP + ACMG metabolic ranges)
Plasma Threonine
| Age Group | Reference Interval |
| Adults | 70 – 190 µmol/L |
| Children | 80 – 200 µmol/L |
| Newborns | 100 – 300 µmol/L (immature pathways → higher) |
Clinical Flags
- > 250 µmol/L → evaluate for metabolic disorder or liver disease
- > 500 µmol/L → strong metabolic abnormality (organic acidemias / GCS defect)
Diagnostic Uses
1. Inborn Errors of Metabolism
- Organic acidemias
- MSUD
- Threonine dehydratase defects
- Mitochondrial disease
- Glycine cleavage system defects
2. Nutritional Disorder Evaluation
Threonine reflects protein intake and catabolism.
3. Liver Disease
Altered clearance and amino-acid imbalance.
4. Neonatal Screening
Newborns often have elevated threonine; interpret age-appropriately.
5. Gut Mucosal Disorders
Low threonine may reflect heavy mucin turnover.
Analytical Notes
- Fasting plasma preferred
- Avoid hemolysis - alters amino-acid profile
- Immediate deproteinization recommended for accurate results
- Assays: HPLC, tandem MS/MS
- Levels vary by age and nutritional status
Clinical Pearls
- Newborn threonine values are naturally higher due to hepatic immaturity.
- Very high threonine suggests possible glycine cleavage or organic acidemia disorders.
- Interpret together with serine, glycine, valine, leucine, isoleucine, and lactate.
- TPN often elevates threonine substantially.
- Threonine is crucial for gut mucin - low levels may worsen IBD symptoms.
Interesting Fact
Threonine and isoleucine are the only two amino acids with two chiral centers, making them structurally unique.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acids
- ACMG Guidelines - Plasma Amino Acid Interpretation
- Mayo Clinic Laboratories - Amino Acid Panel
- ARUP Consult - Amino Acids
- NIH / MedlinePlus - Amino Acid Disorders