Vitamin B12 test

It measures all the vitamin B12 in your blood (its scientific name is cobalamin). Part of it is kept in reserve and a smaller part is ready to be delivered to your cells, and this test counts both together. Next to your number you'll see the lab's reference range, so you can tell at a glance whether you're inside it.

B12 does more jobs than most people think. It helps you make red blood cells, the ones that carry oxygen around your body, it keeps your nerves protected and working properly, and it helps every cell in your body renew itself. When there isn't enough of it, your body makes fewer red blood cells, bigger ones that don't work as well, so less oxygen gets where it needs to go. That's why feeling tired and short of breath are usually the first things people notice.

Low B12 usually creeps in slowly, so the first signs are easy to blame on a busy month or bad sleep. The most common one is tiredness that doesn't lift even after a good night's rest, sometimes with feeling weak or out of breath on the stairs. Your skin might look paler than usual, and your tongue can get sore, red and unusually smooth, sometimes with mouth ulcers.

Because B12 also looks after your nerves, some signs of B12 deficiency show up there: pins and needles or numbness in your hands and feet, feeling a little less steady when you walk, forgetting things more often, finding it harder to focus, or feeling low and irritable without a clear reason. All of these can have other causes too, from low iron to stress, and a B12 test tells you whether B12 is one of them.

Some people run low much more easily than others, usually because of what they eat or how well their body absorbs it. It's worth testing if any of these sound like you:

• You eat little or no meat, fish, eggs or dairy, because B12 comes almost only from animal foods.
• You're over 50, because your stomach makes less acid as you get older, and you need that acid to get B12 out of your food.
• You take metformin or medication for stomach acid, like omeprazole, as both can make it harder to absorb B12 over time.
• You have a gut condition or have had gut surgery, such as coeliac disease, Crohn's or weight-loss surgery.

It's also a good idea if you're planning a pregnancy, drink alcohol regularly, or have noticed any of the signs above. And if you already take B12 supplements, this is how you find out whether they're reaching your blood.

B12 is made by bacteria, and we get it mostly from animal foods. Clams, mussels and liver have the most, then fish like sardines, salmon and tuna, then meat, eggs, milk, yoghurt and cheese. If you eat plant-based, your reliable sources are fortified foods, like some plant milks, breakfast cereals and nutritional yeast, and supplements.

Eating B12 and absorbing it are two different things, though. First your stomach acid has to free it from your food, then a protein your stomach makes has to carry it through your gut into your body. If either step struggles, you can eat plenty and still run low, which is why your plate can't tell you what your blood can.

Most of the B12 in your blood is in reserve, and a smaller part, called active B12 (holotranscobalamin), is the share attached to the protein that delivers it to your cells. This test measures the total, which is the B12 test most people know and search for. If you want to see the delivery share too, you can add active B12 to the same blood draw and get both numbers side by side.

Check the preparation shown with your order. A B12 test on its own usually doesn't need fasting, but if you add tests that do, like glucose or cholesterol, you'll need 8 to 12 hours without food, with water only. If you take B12 supplements or injections, let the lab know, since they push your number up, and never stop a treatment you've been prescribed just to prepare for the test.

You buy your test online and go to one of our partner labs in Barcelona, Madrid, Valencia or Málaga, with no referral needed. In Barcelona and Madrid you walk in during collection hours, and in Valencia and Málaga you go with an appointment. It's one quick blood draw.

Where can I get a vitamin B12 test in Barcelona, Valencia, Madrid or Málaga?

With Diagnostic Station, you can get a vitamin B12 test in Barcelona, Valencia, Madrid and Málaga without asking your GP for a referral. You buy it online and go straight to one of our partner labs, walking in during collection hours in Barcelona and Madrid, or with an appointment in Valencia and Málaga. While you're there, you can add active B12, folate or ferritin to the same blood draw, so one visit answers more than one question.

Should I stop my B12 supplements before the test?

You can keep taking them. Your number will include what your supplements add, so you'll see your level with them in the mix. If you'd rather see your level without over-the-counter supplements, ask the lab whether to pause them for a few days first. Prescribed injections or tablets are a different story: keep taking them as prescribed.

Can vegans get enough vitamin B12?

Yes, just not from plants alone. Vegans get their B12 from fortified foods and supplements, and a blood test is the simplest way to see whether your routine is giving your body enough.

What are the signs of B12 deficiency?

The most common are tiredness, weakness and getting out of breath easily, along with pale skin, a sore or smooth tongue, mouth ulcers, pins and needles in your hands or feet, and changes in memory, focus or mood. Lots of things can cause these, which is why a blood test helps.

Is vitamin B12 included in a general blood test?

Usually not, and that includes our general check-ups. The good news is you can add it to the same blood draw and check everything in one visit.

What's the difference between vitamin B12 and folate?

They're two different B vitamins that work as a team, since your body needs both to make healthy red blood cells. Folate comes mostly from leafy greens, beans, lentils and fortified foods, and you can test it in the same blood draw as your B12.

This content is for information only and doesn't replace medical advice.