Vitamin B12
Measures B12 (cobalamin) in your blood. Nerves and red blood cells use it every day; low levels can track with diet, stomach or gut absorption issues, or medicines that block uptake.
Vitamin B12 helps you build healthy red blood cells and keep nerve insulation in good shape. Most people pull it from animal foods or fortified products; stomach acid and a protein called intrinsic factor have to cooperate so the gut can absorb it. When stores run low, symptoms can creep in slowly: numbness, balance trouble, brain fog, or anemia on a CBC. Doctors order serum B12 when diet, medicines, or gut surgery raises the odds of shortage, and when blood counts look oversized. Borderline numbers sometimes need a second look with other markers because the serum test is not perfect. One lab value is a clue, not the closing argument.
Self-Pay Price Comparison
| Provider | Price | vs. Highest | Order |
|---|---|---|---|
Quest QuestHealth self-pay | $49.00 | Highest | Order · Quest |
LabCorp Labcorp OnDemand | $49.00 | Highest | Order · LabCorp |
GoodLabs Discount lab network | $10.00Best value | Best price | Order · GoodLabs |
What This Test Measures
Serum B12 is reported as a single cobalamin level, usually in picograms per milliliter. Here is what that storage snapshot is telling you:
Serum concentration of the vitamin that supports nerves and red blood cells; low points to diet gaps, absorption loss, or medicines blocking uptake, high usually reflects a recent injection or high-dose supplement rather than extra neurologic benefit.
How to Read Your Results
Labs print their own pg/mL band, and symptoms can disagree with the number. Here is how to read the three usual result stories:
| Marker | Normal Range | If Flagged | What It Might Mean |
|---|---|---|---|
| Serum vitamin B12 (general adult) | MedlinePlus Vitamin B12 Test: many laboratories cite roughly 200-900 picograms per milliliter (pg/mL) as a common adult band; pediatric and pregnancy ranges differ. | abnormal | MedlinePlus notes symptoms can still appear when the number looks low-normal. Your doctor may add methylmalonic acid or homocysteine when the story and the level disagree. One result in isolation rarely tells the full story. |
| Serum vitamin B12 (low) | Below the laboratory low limit; thresholds vary slightly by lab method. | low | Fits low intake, malabsorption, pernicious anemia, or post-surgical loss. Replacement plans range from oral high-dose cobalamin to injections depending on cause and symptoms. |
| Serum vitamin B12 (high) | Above the laboratory high limit or unexpectedly high while taking supplements. | high | Often reflects recent B12 shots or high-dose vitamins; less often liver disease or blood disorders. Your doctor interprets it next to symptoms and other labs. |
When to Order
Annual baseline
Universal yearly B12 screening is not standard for everyone, but many clinicians add it when diet risk, anemia workups, or nerve symptoms enter the chat.
Vegan diet or very limited animal foods
Plants do not carry reliable B12 unless fortified; a level shows whether pills or injections need to join the plan.
Metformin, long-term acid reducers, or ileum disease
Those factors blunt absorption even when intake looks fine on paper.
Large red blood cells on a CBC or unexplained neuropathy
B12 shortage is one classic thread your doctor checks alongside folate and other causes.
Stomach surgery or known pernicious anemia
Intrinsic factor loss or bypassed gut segments change how B12 is replaced; levels guide how aggressive therapy should be.
Prep & Logistics
- Fasting
- Typically no fasting
- Sample
- Blood draw
- Results
- Usually 24-48 hours; many portals update the same day or the next.
- Referral
- Often self-order (check local rules)
- Markers
- Serum vitamin B12 (cobalamin), usually reported in picograms per milliliter (pg/mL).
Tests That Pair With This One
RBC folate when large red cells or anemia could be folate-driven instead of B12-driven.
Iron stores when fatigue overlaps anemia and diet limits heme iron.
Full count and indices when B12 is low and cell size or hemoglobin needs a hard look.
FAQ
Serum B12 looks normal—do I still need methylmalonic acid or homocysteine?
Sometimes. Borderline B12 with neuropathy, anemia, or gut surgery can still be a B12 problem. Your doctor may add methylmalonic acid or homocysteine when the serum level and the story disagree.
My level is 280 pg/mL but I have tingling. Is that normal?
Maybe not for you. MedlinePlus notes people can feel effects even when the printed value is borderline. Your doctor may repeat the test, check methylmalonic acid or homocysteine, or simply treat based on the overall picture.
Do I need to fast?
Usually no. MedlinePlus states most B12 tests need no special prep unless paired with other labs that do.
Can folic acid hide a B12 problem?
High folate can improve blood counts while nerve damage from low B12 still advances. That is why doctors look at both when macrocytosis shows up.
Sources
Prices pulled directly from provider websites and verified by hand. Reference ranges sourced from MedlinePlus. Not generated by AI.
- GoodLabs - product page (pricing context)(verified 2026-03-23)
- Quest - consumer lab shop (pricing context)(verified 2026-03-23)
- LabCorp OnDemand - vitamin B12 test (pricing context)(verified 2026-03-23)
- MedlinePlus - Vitamin B12 Test overview
- MedlinePlus Medical Encyclopedia - Vitamin B12 level
- Clinical context: LabRecon editorial team. Not medical advice. For informational use only.
Serum cobalamin quantification. Used to evaluate B12 deficiency, macrocytic anemia, and peripheral neuropathy.