Serum Vitamin B12Content and Unsaturated Vitamin B12-Binding Capacity in Myeloproliferative Disease

Abstract

The serum unsaturated vitamin B₁₂-binding capacity (UBBC) was found to be of value in distinguishing polycythemia vera from other conditions that are accompanied by an elevated hematocrit or an absolute erythrocytosis and as an indicator of disease activity in polycythemia vera. The serum vitamin B₁₂ level was of lesser value. Increased levels of serum vitamin B₁₂ were observed in 36% and increased levels of UBBC in 70% of patients with untreated polycythemia vera and related myeloproliferative disorders, as contrasted with normal serum vitamin B₁₂ levels in 98% and normal UBBC in 87% of cases of spurious (relative) polycythemia and isolated erythrocytosis (secondary and unclassified polycythemia). Serum vitamin B₁₂ and UBBC levels in polycythemia vera treated only with phlebotomy did not differ from values in untreated cases, whereas patients whose erythroid activity had been controlled by myelosuppressive therapy had levels comparable to those in normal subjects. UBBC values were positively correlated with erythroid activity and leukocyte count. Serial observations indicated that changes in UBBC accompanied and in some cases preceded the occurrence of response and relapse in patients receiving myelosuppressive therapy. Changes in serum B₁₂ levels did not parallel the erythroid response to therapy, nor were B₁₂ levels correlated with the blood count, spleen size, or uric acid values. Chromatographic separation of unsaturated B₁₂ binders showed an increase in both alpha and beta components. The frequent observation of elevated B₁₂ binders without a concomitant rise in serum B₁₂ content in patients with polycythemia vera suggests that some of the B₁₂-binding protein of alpha mobility that is elaborated is abnormal in that it does not bind endogenous vitmain B₁₂.