Plasma total transcobalamin I. Ethnic/racial patterns and comparison with lactoferrin.

Plasma total transcobalamin (TC) I levels were measured in 434 healthy volunteers by radioimmunoassay (RIA). The results were analyzed for demographic patterns and were compared with lactoferrin, cobalamin, homocysteine, and chemistry panel results. Plasma TC I was higher in blacks than in other ethnic/racial groups and higher in women than in men. TC I levels did not correlate with lactoferrin levels. Lactoferrin showed significant ethnic differences also, but, unlike TC I, its levels were highest in whites. TC I levels correlated with cobalamin but not homocysteine levels. Neither TC I nor lactoferrin correlated with chemistry panel results, including creatinine, total protein, albumin, lactate dehydrogenase, and alkaline phosphatase levels. The demonstration with an RIA that directly measures total TC I that plasma levels are significantly higher in blacks than in other groups may explain the well-known higher cobalamin levels in blacks. Surprisingly, plasma lactoferrin, which has the same cellular sources as TC I, does not correlate with plasma TC I levels and shows dissimilar demographic patterns; lactoferrin levels are highest in whites. These findings suggest that regulation and/or secretion of these 2 proteins differ even though their localization and expression patterns in myeloid precursors are similar.