Transcription
Hey guys, welcome back to my channel. As I've promised, I'll talk about Schilling tests. In my previous video, I've talked about vitamin B12 deficiency, and the Schilling test was one of the methods used to diagnose B12 deficiency. So, do we use it anymore? No. Why? There are some limitations to this test. However, it's a very good board question because it has a lot of, like, mechanisms and pathophysiology. And if you understand the Schilling test, that means that you understand B12 absorption, which is a huge deal for the boards and for you to understand pernicious anemia as well as megaloblastic anemia.
So, in brief, the Schilling test is giving the patient radioactive B12, okay, and then measure the B12 in the urine to see if this patient is absorbing B12 or not. So let's get started. So, if you haven't already watched my last video on B12 deficiency, I strongly encourage you, in the strongest possible words, to go ahead and watch my previous video first, because you will never understand anything if you have not. Anyways, B12 deficiency has many steps, as I have described in my last video, so you know all of them. Let's add a couple more. So we have different causes of B12 deficiency: dietary deficiency, salivary gland disease, pernicious anemia, pancreatitis, ileal disease or resection. Also, we have bacterial overgrowth. If you have many awesome bacteria here in the gut, they are eating your vitamin B12, so you are not absorbing any B12. This is called bacterial overgrowth; sometimes it's called small intestine bacterial overgrowth, or small bowel bacterial overgrowth syndrome, whatever. Other causes of B12 deficiency will include liver disease. Why is that? Because once you are here in the bloodstream, B12 has two destinations: either to go to cells to be utilized or go to the liver to be stored for years. So liver disease will cause kind of vitamin B12 deficiency because the store is malfunctioning. It's like if you are like, as CEO of the company, you have a lot of inventory; however, the place where you store your inventory is damaged. You will lose a lot of money. This is a no-brainer.
So now we have seven different causes of B12 deficiency. So, bacterial overgrowth will be six; liver disease will be seven. So here comes our hero, the Schilling test. We know that it's probably B12 deficiency, but why? Is it pernicious anemia? Is it diet? Is it the bacterial overgrowth? Is it malabsorption syndrome? Or the famous fish tapeworm, Diphyllobothrium latum, or liver disease? Which one? The Schilling test kind of gives us an idea of which one is the cause, or whether the patient has B12 deficiency or not. So, do you have B12 deficiency, and if so, why?
So bear with me; many steps for the Schilling test. First, we give oral vitamin B12 plus intramuscular. Which one will be absorbed more quickly? Answer: intramuscular, of course. The intramuscular B12 will go to the bloodstream; it will saturate all of your transcobalamin receptors, so all of them are being used. I have no more transcobalamin to carry anymore B12, so the oral one has only one destination: to end up in the urine. Why? Because there are no more receptors to carry it through the bloodstream, so it will end up in the kidney. When it's bound to transcobalamin, it cannot be filtered; when it's free, it will go to the urine, which you will pee. So, when it's free, you will pee; when it's bound, it's bound. Anyway, this is the first step. I saturated all of my receptors, and I gave oral B12. Let's measure the urine B12 because it's radioactive, so it shines, and let's measure it. If it's 10% or more, that's okay in the first 24 hours. This patient is either normal or is not eating enough B12 in the diet, so it's either normal or a dietary problem, which is easy to fix; just make him eat more B12 or give it to him intramuscularly. Okay, if it's less than 10%, oh, there's a problem. Let's go to step number two. I will give them the B12 plus the intrinsic factor. What if the result in the urine normalizes and it's now more than 10 percent? So it increased. First step, it was less than 10 percent; second step, it's increasing. This means I'm fixing the issue. What's the issue? Intrinsic factor deficiency, i.e., pernicious anemia. Wow, problem solved. This patient has B12 deficiency due to pernicious anemia. Done.
What if the result is still less than 10 percent? Let's go to the third step: B12 plus antibiotics. Why? I would like to destroy these fancy bugs. What if giving B12 plus antibiotics normalizes the urine value of B12? Done. I've diagnosed this patient has B12 deficiency due to bacterial overgrowth syndrome. Okay, still did not normalize. Let's go to the next step: B12 plus, I'm sorry, pancreatic enzymes such as protease or the pancreatic secretions. What if it normalizes and it's more than 10 percent? So this patient has chronic pancreatitis; the pancreas is damaged and demolished and in a very bad shape.
So, in summary: if the first step was normal, it's either a normal patient or a dietary deficiency. If the first step was decreased, so we have less cobalamin in the urine, however the second step normalized it, this is pernicious anemia. If both first step and second step yield less B12 in urine, this is malabsorption; could be bugs, could be pancreatic enzyme deficiency, could be ileal resection, Crohn's disease, fish tapeworm. So this test kind of had some limitations, but pernicious anemia is easily diagnosed with this test; also, bacterial overgrowth will be like just like that. So this was the Schilling test.
What are the limitations of the Schilling test? It's expensive; radioactive elements; sometimes the radioactive cobalamin is not available; time-consuming. I have to do step one, wait 24 hours to collect the urine, then step two, then step three. And don't forget, treatment makes much more sense. If you suspect this patient is having B12 deficiency and you give him some nice intramuscular B12, and now he's fine, well then no worries; you don't have to do this stupid Schilling test. Okay, but for board questions, it's probably going to be the wrong answer. So if it says, like, this patient has anemia symptoms, neurological symptoms, which of the following is the best step, best next step in management? Probably give him an intramuscular shot of B12. The Schilling test will likely be the wrong answer. Why? As you know this, and for the boards, always think cheap. If you have two choices that look equally plausible, one of them is very expensive, like radiologic stuff and like MRI or CT angiography or whatever, and another step is very cheap, usually the answer is the cheaper option. They would like you to think cheap first instead of just ordering a bunch of tests.
Now, question of the day: which famous class of medication can cause bacterial overgrowth syndrome? Please let me know in the comments. And if this is the twelfth question to get the previous ones, go to my Facebook page: www.facebook.com/news.about.syria