Nonleukemic elevation of serum vitamin B₁₂ and B₁₂-binding capacity levels resembling that in chronic myelogenous leukemia

In vitro serum vitamin B₁₂ abnormalities characteristic of chronic myelogenous leukemia were found in 5 patients without leukemia. All had leukocytosis, and 3 transiently had immature myeloid cells in peripheral blood. The B₁₂ abnormalities were: (1) marked elevation of alpha-globulin B₁₂-binding capacity in all subjects and (2) high serum B₁₂ levels in 3 patients with high-normal levels in 2. Beta-globulin binding was normal in 2 but elevated in the others. Electrophoretic and reticulocyte uptake studies also demonstrated the findings seen in chronic myelogenous leukemia. Of 3 patients studied at different stages, one's abnormalities disappeared as leukocytosis subsided, one's improved similarly but quickly rebounded as leukocytosis returned, and the third remained abnormal as leukocytosis persisted. A patient recovering from agranulocytosis due to chemotherapy was studied serially. The B₁₂ abnormalities paralleled the recovery phase to the exact day, returning to normal as leukocytosis subsided. High alpha-globulin B₁₂ binding and, often, serum B₁₂ levels resembling those in chronic myelogenous leukemia, thus, are not infrequently found in nonleukemic leukocytosis. The exact mechanisms responsible remain unknown. However, it is apparent that the abnormality is not an expression of the leukemic process itself and is not diagnostic for the disease.