Three-Month Follow-Up

On subsequent office visits, the patient reported that she had regained her previous state of health. At one of these, testing

had identified the presence of anti­intrinsic factor antibody and a markedly elevated serum gastrin level. At the three-month follow-up visit, the hemoglobin level was 11.3 gm/dL; MCV, 72 µm3; RDW, 12.9%; white blood cell count, 7,200/mm3; and platelet

count, 280,000/mm3. The stool was negative for occult blood. The monthly B12 injection was administered, blood was obtained for further tests, and the patient was started on oral ferrous sulfate, 325 mg three times a day. The blood test results were

ferritin, 72 µg/L; iron, 91 µg/dL; iron binding capacity, 288 µg/dL; haptoglobin, 187 mg/dL (normal, 50-220); B12, 2,450 ng/L; and folate, 9.8 µg/L. Upper gastrointestinal endoscopy was performed a week later. Atrophic gastritis with antral sparing and an antral polyp were detected. The polyp was excised and determined to be a gastric carcinoid.

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.