Fatigue is one of the most common complaints patients have. The causes are endless, and as a result, many people are not ever diagnosed properly. Unfortunately, many physicians are no longer able to spend the time necessary to take an adequate and thorough history. The majority of my patients tell me, "my thyroid tests have been checked multiple times and they are fine!" They are almost always checked for anemia and when those tests are normal, it's usually just chalked up to a busy lifestyle or when all else fails, told they have depression or "you're getting older."
An interesting case:
I first saw him several months ago--a successful businessman and father who had been followed for years by his internist. He scheduled an appointment for a screening colonoscopy; however, during the evaluation, it became clear he was worried about fatigue. His physician had done the usual routine lab tests and thyroid testing and all were normal. After an hour discussing his symptoms, family history and medications with me, labs were ordered.
To make a long story short,his B12 level was within the normal range; however, the normal range for B12 is extremely wide and usually falls between 200 and 1100 . I am concerned, however, if the level of B12 in the blood is in the low normal level even if it is around 350. I also check intracellular B 12 to see if there is enough in the cells. His serum methylmalonic acid was sky high indicating severe intracellular depletion.
Further testing revealed he had pernicious (the word means deadly) anemia and needed immediate and lifelong B 12 injections. An easy malady to treat but eventually deadly if missed.
Second opinion consults with a physician that "looks at the whole picture" can definitely be lifesaving in some cases. Oral B 12 would not have been of benefit since testing showed he would not have been able to absorb it.