Interference of deferasirox with assays for serum iron and serum unsaturated iron binding capacity during iron chelating therapy.

BACKGROUND Deferasirox (DFX) is an oral iron chelator that is used worldwide for the treatment of iron overload. Although serum ferritin level is usually measured as a marker of the efficacy of DFX, we sometimes experienced unexplainable changes in other serum markers for iron. We hypothesized that photometric assays for serum iron (sFe) and unsaturated iron binding capacity (UIBC) might be affected by DFX. METHODS Measurement of sFe and UIBC was performed using 4 different assay systems. The samples were prepared by adding 0-300 μM DFX to pooled human serum or 15 randomized human serum samples. In some experiments, DFX-iron complex (DFX-Fe) was prepared by mixing iron ammonium citrate solution and DFX solution. RESULTS Measurement of sFe was influenced by DFX-Fe, while iron-free DFX showed no effect on the value of sFe; DFX-Fe was measured as sFe, undistinguishable from transferrin-bound iron. On the other hand, measurement of serum UIBC was influenced by DFX itself; DFX might have been bound to iron in the reagent used for the assay, leading to an increase in UIBC values. CONCLUSIONS DFX affected the sFe and UIBC assay systems. We must be careful in observing these markers during iron chelation therapy with DFX.