Zero to GP - GP Revision Podcast

Vitamin B12 Deficiency - Essential GP Revision

• Thomas Watchman • Season 1 • Episode 18

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0:00 | 19:47
SPEAKER_01

Hi, this is Tom, and in this episode I'm going to be going through B12 deficiency, all the key stuff you need to know for your GP exams. The format of these episodes, as always, is I'll ask you questions, I want you to come up with your answer, ideally write it down or say it out loud, and then I'll go through the correct answer and an explanation. If you're doing your AKT exam anytime in the next 12 months or even longer, or even if you just want to brush up on your GP knowledge, then I highly recommend checking out the AKT revision resources, like the AKT revision book, which is crammed through, crammed full of all the key facts you need, the zero2gp.com site for practice questions and flashcards, and my upcoming AKT revision course, which is going to be in London on the 13th of September 2026. On a Sunday, we'll go through all the key stuff for the AKT exam. And if you check out the website, there's a link in the description, you can see the feedback and stories from people who've been on the course and done really well in their exam. So that's worth having a look at. But for now, let's get straight into this episode on B12 deficiency. So our first case or our case in this episode is a 62-year-old woman, and she comes in to see you, and she's noticed she's got tingling in both feet. She also notices she's quite unsteady when walking. She's not really sure why, but she feels unsteady. She doesn't feel well planted. And she has three months of gradually worsening fatigue. So my first question to you is based on her tingling in her feet and her unsteadiness, what are the causes of peripheral neuropathy? And I've got quite a few causes to list here, so I'll give you some time to note those down. So for the causes of peripheral neuropathy, and I use this pneumonic all the time, I use the ABCDE pneumonic. A is for alcohol, too much chronic alcohol consumption can cause peripheral neuropathy. B is for B12 deficiency, which is what this whole episode is about. C is for cancer, for example, myeloma or small cell lung cancer, or chronic kidney disease, or sharcomary tooth disease, which is a genetic condition that can cause peripheral neuropathy. D is for diabetes. Diabetes is the most common cause of peripheral neuropathy. And the other one for D is drugs, and we'll talk more about that shortly. And the final one is E for every vasculitis, which is kind of cheating, but just remember vasculitis has a cause. The second question I have for you is what's the first sensory loss in B12 deficiency?

SPEAKER_00

What sensory modality is lost first in B12 deficiency? The answer here is vibration sense.

SPEAKER_01

So if you're examining someone you suspect has uh peripheral neuropathy secondary to uh B12 deficiency, get out your tuning fork if you can find one and test their vibration sense. The third question I have is what's the functional test for proprioception? So proprioception is usually the second the second sensory modality after um vibration sense lost in B12 deficiency. And this will also contribute to her unsteadiness when walking. So what tests could you do in your clinical practice in the room with the patient to test for their proprioception in their peripheral nerves? So the key test is Romberg's test, where you get them to stand there, close their eyes, make sure it's safe and they're not going to fall over, but they stand there with their eyes closed, and if they lose their balance with their eyes closed, it means proprioception's been lost in their ankles and their lower legs. The other thing you can, of course, do is just test their joint position sense. So move their ankle up or down, toes up and down, and see whether they can tell you whether they are up or down. But the key functional test is Romberg's test. Next question I have is what change would you see or could you see in the mouth in somebody with B12 deficiency?

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What key sign is in the mouth? The key sign is glossitis.

SPEAKER_01

So this is where the tongue becomes inflamed, very smooth, and there's kind of loss of the papilla on the tongue. So here you can see a picture of glossitis, and in B12 they describe glossitis as a beefy tongue. Hopefully you can see this kind of looks like a beefy tongue, but if you see this, think about B12 deficiency. The next question I have is what full blood count findings would you see in B12 deficiency?

SPEAKER_00

So you've done some blood tests on this patient, what findings will you see?

SPEAKER_01

The key finding in B12 deficiency is macrocytic anemia, particularly megaloblastic anemia. So you see a low hemoglobin indicating anemia, and a raised mean corpuscular volume, meaning the red blood cells are big. If it's severe, you can also see a low white blood cell count and a low platelet count as well. Next question I have is what tests will you do specifically for the B12 level? So you have a choice of two tests, you choose one or the other, and what are they? So you can test for the serum cobalamine, and this tests for the total amount of B12 in the blood. If this is low, you can be fairly confident it's B12 uh deficiency, but it may be normal, um, even if somebody has functional B12 deficiency. So you can also test for something called serum holotranscobalamine or holo T uh T C. And this is the active vitamin B12 level. So if the serum holo transcobalamine is low, it means there's a low active B12. The next question I have is what further tests could you do if the B12 levels are indeterminate? So sometimes patients will have a low B12 level even when the B12 levels on the blood tests are normal or borderline. So what further tests could you do to determine whether they do have a B12 deficiency? You can test something called methylmalonic acid or MMA, and this is raised. B12 in the body helps to break down, to oversimplify this, B12 in the body helps to break down methylmalonic acid. So if you have B12 deficiency, the methylmalonic acid levels build up because it's not being broken down or metabolized. So a high methylmalonic acid level suggests B12 deficiency. Okay, so you've got a 62-year-old woman, she's got feet tingling, she's unsteady on her feet, she's experiencing fatigue, she has macrocytic anemia on her full blood count, and her serum cobalamine level is low. So my next question for you is what medications can cause B12 deficiency? This is a key point. Often when a patient has low B12, the first thing I look at is what medications are they on, because that's a common cause of low B12.

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Key medications are proton pump inhibitors.

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Loads of patients get prescribed proton pump inhibitors and they're kind of seen as harmless, but they can cause B12 deficiency. They're not kind of harmless medications. So that's a key one to remember. The other one is metformin. Metformin is a fantastic medication for diabetes, has all sorts of benefits, but it can cause B12 deficiency. The other one, which is not a drug we would prescribe, is nitrous oxide. And nitrous oxide is often used recreationally, and that can cause quite significant B12 deficiency with neurological symptoms. So ask patients about recreational nitrous oxide use.

SPEAKER_00

My next question for you is what is the autoimmune cause of B12 deficiency? The answer is pernicious anemia. The next question is, what's the test for pernicious anemia? The test is to check for intrinsic factor antibodies.

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So my next question for you is what's the very basic pathophysiology of pernicious anemia?

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So we need to go through some very basic physiology.

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There's parietal cells in the stomach that make something called intrinsic factor. This intrinsic factor is essential for vitamin B12 absorption and it's absorbed in the terminal illium. In pernicious anemia, there's antibodies against either the parietal cells that make the intrinsic factor or the intrinsic factor itself. And remember we test specifically for intrinsic factor antibodies. It is possible to test for parietal cell antibodies, but this is kind of less useful in a second-line test. Mainly we test for intrinsic factor antibodies. So if you've got these antibodies against parietal cells or the intrinsic factor, that means less or no intrinsic factor in the system. That intrinsic factor means that the B12 is not absorbed in the terminal illium. So essentially, this essential component for B12 absorption is missing because antibodies have destroyed it. Okay, so we've got a 62-year-old woman, feet are tingling, she's unsteady, she's got fatigue. Let's say intrinsic factor is negative, so we've kind of ruled out pernicious anemia, and she takes no medications.

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What other causes do we need to consider for B12 deficiency?

SPEAKER_01

We need to think about dietary causes, so ask about the diet. And B12 is mostly found in animal products. So um a vegan diet or a diet that excludes animal products like fish, meat, eggs, that kind of thing, uh, can be low in B12, although a lot of foods are fortified with B12. So dietary is one factor, the other is malabsorption. So if somebody's got a condition like Crohn's disease that affects the terminal ileum or celiac disease, that can affect B12 absorption and lead to B12 deficiency.

SPEAKER_00

My next question to you is in this patient, what is going to be your initial management as a GP.

SPEAKER_01

Important thing to consider here is she has neurological symptoms. Nice clinical knowledge summaries say that if somebody's got neurological symptoms with B12 deficiency, you need to discuss urgently with a specialist and base your management on specialist advice. Generally, the management will be intramuscular hydroxocobalamine, which is B12, one milligram, and in somebody with neurological symptoms, that they're giving they're given an injection on alternate days, so one today, not tomorrow, the next day, and so on, until there's no further improvement in their neurological symptoms, until they start to plateau. This could be quite a few injections. My next question is what about if she had no neurological symptoms?

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How would you manage this patient? So essentially, you need to address the underlying cause.

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So let's say she's recreationally taking nitrous oxide, tell her to stop that. If there's an appropriate medication to stop, maybe stop that. If there's a dietary insufficiency, address that, and so on. So you address the underlying cause. Then you have a choice of either giving intramuscular hydroxycobalamine, so intramuscular B12, and if there's no neurological symptoms, the initial regime is to give her an injection three times a week, so Monday, Wednesday, Friday, for two weeks as the initial kind of loading thing to treat the B12 deficiency. Or the alternative option, for example, if it's a dietary cause, is to give oral cyanocobalamine, which is oral vitamin B12. Okay, so you've got the 62-year-old woman, she's got these symptoms, she has a low B12 level, and let's say she's treated with injections. So she has her low, she has a loading dose of injections and no further symptoms.

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The question I have for you, the next question is what would be the follow-up blood test that you would need to arrange.

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The nice clinical knowledge summaries say you should arrange a full blood count and reticulocytes count and check these at seven to ten days of treatment and also at eight weeks of treatment. At seven to ten days, the reticulocyt count should come up. Reticulocytes are kind of newly represent newly produced red blood cells. So this will show that the bone marrow started producing more red blood cells if the reticulocyte count has gone up. And at eight weeks, everything should be back to normal. So they should, she should no longer have anemia, her mean corpuscular volume should be normal, and everything should basically be returned to normal. There's no need to check the B12 levels. At eight weeks, they also recommend checking the iron and folate level to check that there hasn't been a masked iron deficiency anemia or folate deficiency. My next question is: what would be the long-term management for this patient? So let's say you check their follow-up blood tests, everything, the treatment is working as expected, she's getting better.

SPEAKER_00

What's your long-term management?

SPEAKER_01

So in this patient with neurological symptoms, she's highly at risk of uh developing B12 deficiency again with further neurological symptoms. So we need to make sure that doesn't happen. So the long-term management in this patient will be intramuscular injections of hydroxycobalamine, one milligram, every two months. And that's essentially for life. My next question is: what would be the long-term management if she didn't have any neurological symptoms? She's had the initial treatment, she's getting better, but she she never had neurological symptoms, just B12 deficiency anemia.

SPEAKER_00

Here you have a choice.

SPEAKER_01

Either it could be intramuscular hydroxycobalamine, one milligram, every two to three months, so eight to twelve weeks. Or the other option is daily oral cyanocobalamine, so the B12 tablets. And this is if it's a dietary cause, or say it's due to medication and she's not absorbing as well as she could do. My final question for you on vitamin B12 deficiency is let's say you give her oral cyanocobalamine.

SPEAKER_00

When should she take the oral treatment?

SPEAKER_01

The advice is to take the tablets between meals. So you don't want to take, you want to essentially take them on an empty stomach between meals, not with meals or food or other medications that could affect the absorption. So thanks for listening or watching this episode on B12 deficiency. Hopefully, you found it helpful. At this point, I would recommend heading to the description of this video. Check out the AKT revision course, which is coming up on the 13th of September this year. Have a look at what some people who've been on the course and gone on to do well in their exams have written. And uh don't take my word for it. Have a look at what people who've actually sat the course have said about it. And I hope to see you there. But if not, I'll see you either way in the next episode, which will be next week.