According to Harrison’s Principles of Internal Medicine, 18th edition, page 870, the diagnosis of vitamin B12 deficiency requires measurement of methylmalonic acid. Either this test was not performed on the 76-year-old woman described in the article, or the result was not entered. Without a methylmalonic acid level, the title of this article seems incorrect, or the article itself is incomplete by not including this level. The correct diagnosis of anemia due to an intestinal tapeworm was made by capsule endoscopy. She received appropriate therapy and her anemia cleared quickly.
If there is an updated concept for diagnosing vitamin B12 deficiency, I’m open to learning about it.