Vitamin B12 deficiency: symptoms, testing, and when injections are appropriate

Clinically reviewed by James Singh, Registered Nurse and Advanced Nurse Practitioner, Mango Medical.

If you have been feeling exhausted, foggy or “not quite yourself” for weeks, vitamin B12 deficiency is one possible medical cause worth considering, particularly if you have relevant symptoms or risk factors. It is common, it develops slowly – the body’s B12 stores can take two to five years to run down – and it is simple to test for. A straightforward blood test can measure your B12 and folate levels, and if a deficiency is found, treatment is usually tablets or injections depending on the cause. Most routine results are back within around 24 hours, so there is no reason to spend months wondering.

One thing matters before anything else: the NHS advises seeing a GP if you have symptoms of B12 or folate deficiency, because it is important that a deficiency is diagnosed and treated as soon as possible – particularly when it is affecting your nervous system. A private blood test can sit alongside that advice: it can check your levels quickly, but it is not a substitute for assessment of persistent or concerning symptoms.

The symptoms worth paying attention to

B12 deficiency anaemia causes a recognisable group of symptoms, and some of them also appear in people who are deficient but have not yet developed anaemia. The NHS lists:

• feeling weak or tired
• a sore or red tongue, sometimes with mouth ulcers
• pins and needles
• headaches
• palpitations
• rapid breathing or shortness of breath
• loss of appetite, indigestion or diarrhoea
• problems with your vision
• problems with memory, understanding and judgement

B12 deficiency can also affect the brain and nervous system. Those symptoms include numbness, muscle weakness, problems with balance and coordination, and psychological problems ranging from mild depression or anxiety to confusion. Neurological symptoms are the reason not to sit on this: if you have numbness, tingling in your hands and feet, or balance problems, see a GP promptly.

Two honest caveats. First, every one of these symptoms has other possible causes – tiredness alone is far more often about sleep, stress and lifestyle than about B12. Second, symptoms and blood levels do not always line up: some people have clear symptoms with seemingly normal levels, and some people have low levels with no symptoms at all. That is why the NHS takes symptoms into account alongside test results rather than treating a number as the whole answer.

What causes B12 deficiency

Autoimmune gastritis, historically often referred to as pernicious anaemia, is an important cause of vitamin B12 deficiency – and the most common cause in the UK. Your stomach produces a protein called intrinsic factor, which your body needs to absorb B12 from food. In autoimmune gastritis the immune system attacks the cells that produce it, so no matter how good your diet is, the B12 cannot get through. It is more common in women around 60, in people with a family history of it, and in people with another autoimmune condition such as Addison’s disease or vitiligo. If your results suggest a deficiency, your GP may arrange further tests to check for it – those tests are not always conclusive, but they usually give a good idea. The current NICE guidance (NG239, Vitamin B12 deficiency in over 16s: diagnosis and management) covers how B12 deficiency is diagnosed and managed: https://www.nice.org.uk/guidance/ng239

Other causes the NHS names:

• Diet. Meat, fish, milk and eggs are the main sources. People on a vegan diet who do not take supplements or eat fortified foods are at risk. Because body stores last two to five years, problems can surface years after a dietary change.
• Stomach conditions or surgery. A gastrectomy (removal of part of the stomach) increases the risk, as does previous bariatric (weight-loss) surgery.
• Intestinal conditions. Crohn’s disease and coeliac disease can stop the gut absorbing enough B12.
• Medicines. Proton pump inhibitors (PPIs), H2-receptor antagonists (another type of indigestion medicine), metformin and nitrous oxide can all reduce B12 levels.
• Older age. Absorption tends to fall with age, so deficiency becomes more common in later life.

If any of these apply to you and you have symptoms, a test is a sensible next step rather than a guess.

The tests that check it

A diagnosis is usually made from your symptoms plus blood tests. The tests check whether your haemoglobin is lower than normal, whether your red blood cells are larger than normal, and the levels of B12 and folate in your blood. Folate is checked alongside B12 because the two deficiencies produce very similar pictures – and because treating the wrong one can cause problems, as explained below.

At Mango Medical, the relevant options from the published Price List are:

Test or package	What it covers	Price
B12 & Folate	Total vitamin B12 and folate (2 tests)	£58
Tired all the time (anaemia) profile	Full blood count, ESR, iron/TIBC, ferritin, vitamin B12 and red-cell folate	£140

The £58 test answers the direct question. The £140 profile makes sense when tiredness is the main symptom and you want the wider picture, because it also checks the other common causes – anaemia, iron status and inflammation. It does not include thyroid function, vitamin D or HbA1c, so it is not a full “tiredness workup” in one draw. Bought individually, the full blood count, iron/ferritin and B12/folate elements alone would cost £148, so the profile saves money when you need all of them.

All published prices include clinic blood collection and laboratory processing. The £45 Initial Health Consultation and follow-up consultations are optional extras, not requirements. If any result is concerning, you are advised without charge. Home or workplace collection can be arranged at additional cost, and if your GP has requested specific tests, mention that when booking so the right tests are taken.

When injections are appropriate

Treatment depends on the cause, which is why “just get some B12 injections” is not the right first move. NHS treatment works like this:

• Diet-related deficiency. You may be advised to take B12 tablets every day, or to have a hydroxocobalamin injection twice a year. Vegans who cannot get enough from their diet may need tablets for life; people whose deficiency followed a prolonged poor diet may be able to stop once levels recover and the diet improves.
• Not diet-related – including pernicious anaemia. Usually hydroxocobalamin injections every two to three months for life. In the UK, hydroxocobalamin is preferred over the alternative cyanocobalamin because it stays in the body longer.
• Neurological symptoms. You will be referred to a haematologist and may need injections every two months, with the specialist advising on duration.

Where intramuscular treatment is required, some patients need an initial loading course of more frequent injections before moving onto maintenance treatment. The exact regimen depends on the cause of the deficiency, symptoms and whether there is neurological involvement. Follow-up is tailored to the individual and may include symptom review, neurological assessment, FBC/MCV and further blood testing where clinically indicated.

Where does a private B12 injection fit? Where vitamin B12 deficiency has been confirmed, Mango Medical can assess whether oral or injectable replacement is clinically appropriate. The choice depends on the cause of the deficiency, symptoms, absorption, neurological involvement, previous response and patient preference. Mango Medical offers vitamin B12 injections at £39 and usually gives maintenance B12 injections every 8-12 weeks, but treatment is individualised. In selected patients, including where symptoms recur before the next dose or neurological symptoms persist, injections may be increased to monthly where clinically appropriate, with ongoing review. Injections are not a substitute for investigating why you are deficient in the first place. If you have not been tested, test first; if you have neurological symptoms, see your GP.

The folate trap worth knowing about

Folate deficiency is treated with daily folic acid tablets, usually for about four months. But before prescribing folic acid, a GP will check your B12 levels are normal, because folic acid can improve your symptoms enough to mask an underlying B12 deficiency. If that B12 deficiency goes undetected and untreated, it can still be affecting your nervous system underneath. This is one reason testing B12 and folate together – as the £58 test does – makes more sense than supplementing blind.

GP or a private blood test: how they compare

	NHS GP route	Private test at Mango Medical
Starting point	GP appointment, then a blood test if the GP agrees it is needed	Book a test directly, no referral needed
How soon results come back	Varies; the GP practice advises you	Most routine results within around 24 hours
Cost	Free at the point of use	£58 for B12 & Folate, prices published and include collection and lab processing
What happens to concerning results	GP follows up	You are advised without charge, and can take results to your GP
Best for	Investigating symptoms, diagnosing the cause, prescribing treatment	Fast answers, checking levels, monitoring, tests your GP has requested

The two routes work well together. Many people have a private test for speed and then take the results to their GP for diagnosis and treatment decisions. If your GP has already asked for specific tests, you can have them taken privately – mention it when you book so the right ones are done.

Frequently asked questions

Sources