Serum vitamin B12- binding proteins in neutropenia.

Serum unsaturated vitamin B12-binding capacity (UBBC) has been shown to fluctuate with neutrophil levels and has been reported to correlate with TBGP in normal and hyperleukocytic states. However, the present report demonstrates that the above relationship is not present in neutropenia, suggesting that some of our concepts regarding UBBC may have to be reexamined, since factors other than TBGP appear to be operative. There was a wide scatter of UBBC values among the 39 neutropenic subjects studied, the mean being significantly above normal. There were few low values. High UBBC was primarily confined to subjects with transient neutropenia. Normal values were generally seen in steady neutropenia. The difference in UBBC was primarily due to Transcobalamin I, the other serum binders being similar in both groups. No other significant diagnostic pattern of UBBC was found. Recovery from neutropenia was accompanied by a rise in UBBC in all cases except in four patients whose UBBC was initially very high and fell with recovery. No discernible pattern of serum B12 levels existed, although subnormal levels without evidence of B12 deficiency were found in three of the seven patients with aplastic anemia. Serum B12 levels did not change with recovery in approximately half of the neutropenic subjects, change being variable in the others. Neither serum B12, UBBC, total B12-binding capacity, or any of the three serum B12 binders correlated with neutrophil count, bone marrow findings, TBGP, or granulocyte turnover rate.