Vitamin B12 Test Normal Range: What Your B12 Level Means

What the vitamin B12 test measures

Vitamin B12 (cobalamin) is needed to make healthy red blood cells and to keep nerves working properly. The vitamin B12 test measures how much of it is in your blood, using an ordinary blood sample taken from a vein in the arm.

MedlinePlus explains that doctors usually order the test when other blood tests suggest megaloblastic anaemia, a type of anaemia with large red cells, including pernicious anaemia. It is also ordered for nerve symptoms such as numbness or tingling in the arms and legs, weakness or loss of balance, and when doctors evaluate confusion, dementia or nerve damage (peripheral neuropathy).

At our centre, Vitamin B12 is listed in the diagnostics catalogue. It is often ordered together with a CBC test. Our guide to the vitamin D test covers another vitamin test that is often asked about.

Vitamin B12 test normal range

The MedlinePlus Medical Encyclopedia gives the following values. Your report may show either unit; the two columns are the same values in different units.

Laboratories use different methods and set their own reference ranges, so the range printed beside your result is the one to use. MedlinePlus notes that people with values below 299 pg/mL are likely to have or develop symptoms, and that a deficiency should be confirmed by measuring methylmalonic acid; a high methylmalonic acid level points to a true B12 deficiency.

Is fasting needed? How to prepare

Unlike many vitamin tests, the B12 test usually needs a short fast. MedlinePlus advises not eating or drinking for about 6 to 8 hours before the test. It also lists medicines that can affect the result: colchicine, H2 blockers such as famotidine, metformin, neomycin, para-aminosalicylic acid, phenytoin and proton pump inhibitors such as omeprazole. Do not stop any of these yourself; ask your doctor.

1. Fast for 6 to 8 hours. MedlinePlus advises not eating or drinking for about 6 to 8 hours before a vitamin B12 test. Plain water is usually allowed; ask the lab if you are unsure.
2. List your medicines and supplements. Write down every medicine and supplement you take, including metformin, acid-reducing tablets and any B12 or multivitamin product, and show the list to the doctor or lab.
3. Do not stop any medicine on your own. Some medicines can affect the result, but only your doctor can tell you whether to pause one before the test.
4. Combine fasting tests on one visit. If a fasting sugar, lipid profile or liver panel is ordered on the same sample, follow the longest fasting time among them so that one sample covers all the tests.
5. Bring old reports. Bring earlier B12, CBC and other reports so the doctor can compare the trend rather than one value.

For a general checklist on fasting, water and medicines, see our fasting blood test guide.

What a low B12 result can mean

MedlinePlus lists these causes of a low level:

• Not enough B12 in the diet, which is rare except with a strict vegetarian diet
• Diseases that reduce absorption from the gut, such as coeliac disease and Crohn's disease
• Lack of intrinsic factor, a protein made in the stomach that is needed to absorb B12 (pernicious anaemia)
• Increased body heat production, for example with an overactive thyroid; see our thyroid test guide
• Pregnancy

The NIH Office of Dietary Supplements adds people who have had stomach or intestinal surgery, including weight-loss surgery, older adults (many have less stomach acid, which reduces absorption), and people on long-term metformin or acid-reducing medicines. It notes that babies of strictly vegetarian or vegan mothers can also be at risk.

Symptoms of vitamin B12 deficiency

The NIH Office of Dietary Supplements lists the following symptoms:

• Tiredness or weakness, caused by megaloblastic anaemia
• Pale skin, palpitations, loss of appetite and weight loss
• Numbness or tingling in the hands and feet, and problems with balance
• Depression, confusion, poor memory and, in later stages, dementia
• Soreness of the mouth or tongue

The body stores large amounts of B12, so symptoms can take years to appear. The same source warns that nerve damage can happen even without anaemia, which is why a deficiency should be treated promptly under a doctor's care.

How B12 shows up on a CBC report

A CBC often gives the first clue. MedlinePlus explains that a high MCV, meaning red cells larger than usual (macrocytic anaemia), can be caused by low folate or vitamin B12, as well as by chemotherapy or liver disease. A low MCV points more towards iron deficiency or thalassaemia. Our CBC guide explains MCV, MCH and MCHC.

A doctor seeing a high MCV may then order a vitamin B12 level, a folate level and sometimes methylmalonic acid. The right treatment depends on the cause, for example a low intake compared with a problem absorbing B12, so it should be decided by a doctor rather than by self-medicating.

What a high B12 result can mean

A high level is uncommon, because extra B12 is usually removed in the urine. MedlinePlus lists liver disease such as cirrhosis or hepatitis, and blood disorders such as polycythaemia vera and chronic myeloid leukaemia, among the conditions linked with a raised level. Recent B12 supplements or injections can also raise the result, so tell your doctor about anything you take. If your liver is being checked, see our liver function test guide.

How much vitamin B12 do you need, and where does it come from?

The NIH Office of Dietary Supplements gives these recommended daily amounts, in micrograms (mcg):

B12 occurs naturally in animal foods: fish, meat, poultry, eggs, milk and other dairy products. Plant foods contain none unless they are fortified, and some breakfast cereals and nutritional yeasts are fortified with it. For vegetarian families, milk, curd and paneer are natural sources, and fortified foods or supplements may help; ask a doctor or our dietitian before starting a supplement. The amounts in this table are general guidance, not a treatment dose.