Vitamin B12: rango normal, alto y bajo

En resumenNormal values are 299–1054 pg/mL (219–773 pmol/L). Values below 299 pg/mL (219 pmol/L) are a possible sign of deficiency, which is then confirmed by checking methylmalonic acid in the blood.

Valores de referencia

Grupo	Valor de referencia
Adultos	299–1054 pg/mL (219–773 pmol/L)
Possible deficiencia	Below 299 pg/mL (219 pmol/L)

Normal value ranges vary slightly among different laboratories, and some laboratories use different measurements or test different samples. A low result is confirmed with a methylmalonic acid test.

Rango de referencia vs óptimo — no es lo mismo

Deficiency can occur inside the reference range: neurological symptoms are described below ~300 pmol/L (~400 pg/mL). With symptoms, many clinicians treat 300–400 pmol/L as the lower comfort bound.

Compruebe su valor

Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.

A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.

Qué es este marcador

The vitamin B12 level test measures how much vitamin B12 is in the blood. B12 — cobalamin — gives the body energy and helps keep nerves and blood cells healthy. A low level can cause numbness or tingling in the arms and legs, weakness, and loss of balance, which is why the test is also recommended for certain nervous system symptoms, severe confusion (delirium), loss of cognitive function (dementia), and nerve abnormalities such as peripheral neuropathy.

The test is most often done when other blood tests suggest megaloblastic anemia. Pernicious anemia causes a form of it: the stomach makes less intrinsic factor — the substance the body needs to absorb vitamin B12 efficiently — and the resulting B12 deficiency disturbs red blood cell production.

Results are reported in picograms per milliliter (pg/mL); in picomoles per liter (pmol/L) in many countries. The typical normal range is 299–1054 pg/mL (219–773 pmol/L). Values below 299 pg/mL (219 pmol/L) are a possible sign of deficiency — people with this degree of deficiency are likely to have or develop symptoms — and the finding is confirmed by checking methylmalonic acid: a high level of it indicates a true B12 deficiency.

Preparation includes fasting: no food or drink for about 6 to 8 hours before the test. Several medicines can affect the result — colchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors — so the provider reviews the medication list and decides whether anything is paused; no medicine is stopped without that advice.

Cuando está elevado

Uncommon findingAn increased vitamin B12 level is uncommon — excess B12 is usually removed in the urine.

Enfermedad hepáticaConditions such as cirrhosis or hepatitis can increase the B12 level.

Myeloproliferative disordersBlood disorders such as polycythemia vera and chronic myelogenous leukemia can raise B12.

Cuando está bajo

Not enough B12 in the dietDietary deficiency is rare, except with a strict vegetarian diet — B12 is found mainly in animal products.

MalabsorptionDiseases that cause malabsorption — for example celiac disease and Crohn disease — prevent the intestine from taking up enough B12.

Lack of intrinsic factorWithout this stomach protein the intestine cannot absorb vitamin B12 efficiently — the mechanism behind pernicious anemia.

HyperthyroidismAbove-normal body heat production, for example with an overactive thyroid, increases B12 consumption.

EmbarazoThe need for B12 rises, and the measured level can fall.

Qué puede alterar el resultado

Estos factores pueden alterar el valor sin ninguna enfermedad — vale la pena considerarlos antes de repetir la prueba:

Food and drink within 6–8 hours before the testColchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, proton pump inhibitors

Cómo prepararse

No food or drink for about 6 to 8 hours before the test. The provider should know about all medicines — colchicine, H2 receptor blockers, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors can affect the result — and decides whether any of them are paused; nothing is stopped without that advice.

Cuándo tiene sentido repetir la prueba

A value below 299 pg/mL (219 pmol/L) is a possible sign of deficiency and is confirmed with a methylmalonic acid blood test — a high methylmalonic acid level indicates a true B12 deficiency. The provider then looks for the cause: diet, absorption, or intrinsic factor.

Quién suele revisar este resultado

Un resultado fuera del rango de referencia suele ser revisado por:your GP or primary care doctor; a hematologist if anemia is the concern. Traiga su informe de laboratorio y cualquier resultado anterior a la cita.

Nombres usados en los informes de laboratorio

Su informe puede usar cualquiera de estos nombres:
B12CobalaminCobalamin testPernicious anemia - vitamin B12 level

Unidades y conversión

Medido en:pg/mL

pg/mL = pmol/L

pg/mL × 0.738 = pmol/L. Example: 500 pg/mL = 369 pmol/L. Results are rounded to 2 decimal places.

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Preguntas frecuentes

Why is a second test needed after a low result?

A low B12 value is a possible sign of deficiency, not proof. The confirmation test measures methylmalonic acid: when B12 is truly lacking, methylmalonic acid rises, so a high level of it indicates a true deficiency.

Which medicines distort the result?

Colchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors can all affect the measurement. The provider decides whether any of them should be paused.

Who is at risk of B12 deficiency?

People on a strict vegetarian diet, people with malabsorption from celiac disease or Crohn disease, people whose stomach makes too little intrinsic factor (pernicious anemia), people with hyperthyroidism, and pregnant women.

Fuentes

Vitamin B Test: MedlinePlus Medical Test— MedlinePlus, Biblioteca Nacional de Medicina. Consultado: 29 de agosto de 2026.
Vitamin B12 level: MedlinePlus Medical Encyclopedia— MedlinePlus, Biblioteca Nacional de Medicina. Consultado: 29 de agosto de 2026.

Vitamina B12