Diurnal variations in cobalamin binding plasma proteins

The diurnal variations in cobalamin-binding plasma proteins were studied in 10 healthy volunteers. The unsaturated cobalamin-binding capacities of transcobalamins (TC-II and R-binders), P-cobalamin and P-protein were measured every third hour during 24h. Only small variations within an interval of +/- 20% were found. Highly significant decrements during the night were a uniform finding. After correction for variations of total plasma protein, the changes became less prominent, but still significant for P-cobalamin and P-R-binders. Hence the mean values of P-R-binders and P-cobalamin were 113 and 533 pmol/1 at 9:00 h, and decreased 12 and 8%, respectively, at 3:00 h. When using cobalamin binding plasma proteins in the monitoring of various malignant, haematological and autoimmune disorders, the specimens should, therefore, be collected at defined hours and in a uniform posture.