Vitamin B12 (Serum) with methylmalonic acid (MMA) and homocysteine (Hcy) profile

Published: August 9, 2026Updated: August 16, 2026

This test measures three key markers to assess your vitamin B12 status and potential deficiencies that can affect nerve function and red blood cell production.

Quick summary

["A vitamin B12 deficiency can cause fatigue, numbness, and other neurological symptoms—this test helps identify it early."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC: 40669-4
Short code: RUBV IgM CSF Ql IA
Synonyms: RUBV IgM CSF Ql IA
Category: chemistry
Sample: csf
Container: Sterile tube
Units: N/A
Fasting: false
Population: adult
Sex: all
Age range: 18–65 years
Method: ia
CPT: 82784
Specimen volume: 1-2 mL
Stability: Immediate analysis required, Refrigerated: 1h
Hemolysis max: 200
TAT: 4–24 hours
Order: routine

Why This Test Matters for Your Health

Vitamin B12 is essential for nerve function, red blood cell production, and DNA synthesis. Low levels can lead to anemia, nerve damage, or cognitive issues. This panel checks for B12 deficiency by measuring its direct levels and two related compounds: methylmalonic acid (MMA), which rises when B12 is insufficient, and homocysteine (Hcy), an amino acid that also spikes in deficiency.

What the Test Measures

• **Vitamin B12 (Serum):** Measures the amount of active vitamin B12 in your blood. Low levels suggest deficiency.

• Methylmalonic Acid (MMA): A breakdown product of certain amino acids. Elevated MMA indicates B12 deficiency, even if B12 levels are normal.

• **Homocysteine (Hcy):** An amino acid that rises when B12 or folate is low. High Hcy can also signal risk for heart disease, but this test focuses on its role in B12 deficiency.

Common Causes of Low Levels

Deficiencies can arise from poor diet (e.g., vegan/vegetarian diets), malabsorption (e.g., pernicious anemia, Crohn’s disease), or long-term use of certain medications (e.g., metformin). Chronic kidney disease or liver problems may also affect vitamin B12 metabolism.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Vitamin B12, MMA, and Hcy panel

Frequently asked questions

Can low vitamin B12 levels cause permanent damage?

Early detection helps prevent nerve damage or anemia. Treatment (e.g., B12 injections, supplements) can reverse symptoms if caught quickly. However, long-standing deficiencies may cause irreversible nerve issues, so follow-up testing is important.

What symptoms might this test help explain?

This panel may help diagnose fatigue, weakness, numbness, memory problems, or unusual tingling in hands/feet. MMA and Hcy can also signal other metabolic conditions, like kidney disease or thyroid disorders.

How often should I get this test?

If you have risk factors (e.g., vegan diet, history of stomach surgery, or symptoms like fatigue), your doctor may recommend testing every 1–2 years. If you have known deficiency, retesting may be needed more frequently.

Sources

1
MedlinePlus — Laboratory TestsSource
2
Lab Tests OnlineSource
3
Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy