Pernicious anemia. The expected findings of very low serum cobalamin levels, anemia, and macrocytosis are often lacking.

When patients are examined for possible cobalamin deficiency, great stress is often placed on the presence or absence of macrocytosis and anemia and on how low the serum cobalamin level is. The present study, however, shows that only 45 (64%) of 70 consecutively diagnosed patients with pernicious anemia, the most common cause of cobalamin deficiency, had very low cobalamin levels (less than 74 pmol/L [or less than 100 ng/L]). Anemia was absent in 13 (19%) of the patients, and macrocytosis was absent in 23 (33%) of the patients; such absence was particularly common when cobalamin levels were only slightly or moderately low (74 to 184 pmol/L). Coexisting iron deficiency was responsible for the absence of macrocytosis in nine patients. Of the ten patients with neither anemia nor macrocytosis, neurological disturbance was prominent in six, including four whose only noticeable abnormality was cerebral. These observations indicate that macrocytosis and anemia, two classic features of pernicious anemia, may be overstressed in our diagnostic approach. All subnormal serum cobalamin results are best viewed as pathological until proved otherwise. Emphasis on only very low cobalamin levels risks delaying the diagnosis of pernicious anemia in a substantial proportion of cases, particularly in those without anemia or macrocytosis.