On subsequent office visits, the patient reported that she had regained her previous state of health. At one of these, testing
One month later, the CBC results were unchanged, and the ferrous sulfate was discontinued. Hemoglobin electrophoresis produced normal results, including hemoglobin A2 and hemoglobin F levels.
With treatment under way, the cause of the vitamin B12 deficiency remains to be determined. It is axiomatic that a diagnosis of B12 deficiency indicates a gastrointestinal abnormality unless proven otherwise. The cause does not have to be established immediately, but it should be at some point. Many physicians do not consider this to be important, since treatment and efficacy are the same regardless of whether the problem originates in the stomach or the intestine (i.e., inadequate gastric secretion of intrinsic factor or inadequate intestinal absorption of B12).
The difference does have potential repercussions, however. The gold standard for the diagnosis is the Schilling test-measurement of urinary excretion of radiolabeled oral B12. The test is inconvenient, however, because it requires a 24-hour urine collection. It also involves exposure to radioisotopes, albeit a very small exposure compared with that of many other tests. Unfortunately, few labs make the test and many hospitals do not do it. Fortunately, blood tests are available for detecting antiintrinsic factor antibody and measuring the serum gastrin level. Together, the two tests permit diagnosis of pernicious anemia with 90% to 95% certainty. Pernicious anemia is neither synonymous with B12 deficiency nor its only cause, however. Other causes of B12 deficiency, such as sprue or bacterial overgrowth of the gut, each of which needs specific therapy, cannot be diagnosed by the two blood tests.
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