Technique to remove interference caused by radio-opaque agents in clinical capillary zone electrophoresis

To the Editor: We read with great interest the report “Interference of Radio-opaque Agents in Clinical Capillary Zone Electrophoresis” (1 ). A laboratory sent two similar patient samples for our evaluation. Both patients had received intravenous sodium meglumine ioxitalamate (Telebrix), a radioopaque contrast material that absorbs at 214 nm. The interfering substance was not visible on agarose gels (Paragon SPE), whereas the capillary zone electrophoresis (CZE) results (Paragon CZE 2000) showed a peak in the alpha-2 zone, which may be mistaken for a monoclonal protein (see Fig. 1A). The anomalous peak was not removed by reaction with antisera to any of the immunoglobulins. The samples were then desalted (D-Salt Dextran plastic desalting columns, 5-kDa cutoff; Pierce). Several similar products are available. After capillary electrophoresis, the desalted samples (see Fig. 1B) appeared normal with the questionable peak entirely removed, thus confirming that the interfering substance was of low molecular weight and, therefore, not a paraprotein. The desalting procedure was fast and simple. Clinical laboratories that use CZE could easily use this method to evaluate questionable samples.