Urine Methylmalonic Acid (MMA) Testing
Urine Methylmalonic Acid (MMA) Testing
Urine methylmalonic acid measurement is a highly sensitive metabolic marker for vitamin B12 deficiency and inherited disorders of B12 metabolism.
Key Points:
- Gold standard for functional B12 deficiency assessment
- Essential for diagnosing inherited metabolic disorders
- More sensitive than serum B12 levels
- Critical for newborn screening programs
- Valuable for monitoring treatment response
Clinical Applications
Primary Indications:
- Suspected vitamin B12 deficiency
- Unexplained metabolic acidosis
- Developmental delay
- Failure to thrive
- Seizures
- Hypotonia
- Lethargy
- Recurrent vomiting
Screening Applications:
- Newborn metabolic screening
- Family history of inherited metabolic disorders
- High-risk population screening
- Monitoring known cases
Sample Collection and Handling
Collection Requirements:
- 24-hour urine collection preferred
- Random urine acceptable for screening
- First morning void recommended for random samples
- Sterile container required
- Refrigerate during collection
Special Considerations:
- Avoid contamination
- Protected from light
- Transport on ice
- Process within 24 hours
- Document collection time and volume
- Note recent medications
Reference Values and Ranges
Age-Specific Reference Ranges:
Newborns (0-30 days): 0-10 mmol/mol creatinine
Infants (1-12 months): 0-8 mmol/mol creatinine
Children (1-18 years): 0-5 mmol/mol creatinine
Critical Values:
- Mild elevation: 5-20 mmol/mol creatinine
- Moderate elevation: 20-100 mmol/mol creatinine
- Severe elevation: >100 mmol/mol creatinine
- Critical alert value: >200 mmol/mol creatinine
Result Interpretation
Elevated MMA Causes:
- Vitamin B12 deficiency
- Methylmalonic acidemia
- Combined methylmalonic acidemia and homocystinuria
- Dehydration
- Renal insufficiency
- Bacterial overgrowth
Clinical Correlation:
- Consider serum B12 levels
- Assess homocysteine levels
- Review dietary history
- Evaluate maternal B12 status
- Consider genetic testing
- Monitor trending values
Associated Disorders and Conditions
Inherited Metabolic Disorders:
- Methylmalonic acidemia (MMA)
- MUT gene defects
- MMAA gene defects
- MMAB gene defects
- MMADHC gene defects
- Combined disorders
- Cobalamin C deficiency
- Cobalamin D deficiency
- Cobalamin F deficiency
Treatment Monitoring:
- Response to B12 supplementation
- Dietary protein restriction effectiveness
- Metabolic crisis prevention
- Long-term management success
