Interference and failure: The challenge of high-concentration IgM monoclonal protein in capillary zone...

Capillary zone electrophoresis (CZE) is a standard method for serum protein separation, but its performance can be compromised by IgM monoclonal proteins, leading to false-negative results.

We report a case of Waldenström macroglobulinemia (IgM 56.05 g/L) with repeated CZE failure. Immunofixation electrophoresis (IFE) confirmed an IgM kappa monoclonal protein. Four pretreatment protocols were evaluated: 1) 37°C incubation; 2) dilution with distilled water; 3) dilution with 0.9% saline; and 4) pretreatment with β‑mercaptoethanol (BME). Gel-based serum protein electrophoresis (SPE) and immunosubtraction CZE were also performed to investigate the interference mechanism.

Initial CZE failed to yield an interpretable electrophoretogram. Incubation at 37°C showed no improvement. Dilution with distilled water induced visible precipitation and resulted in a false-negative electrophoretic pattern with a marked drop in measured total protein. Dilution with saline prevented precipitation but still failed to reveal a distinct monoclonal spike, despite biochemical measurements consistent with high globulin levels. In contrast, pretreatment with BME successfully restored a clear monoclonal spike in the β‑γ region on CZE, demonstrating restored solubility and proper migration. IFE corroborated the presence of the IgM kappa monoclonal protein. Gel-based SPE successfully showed a distinct M-protein band without interference, while immunosubtraction CZE failed under both temperature conditions, supporting cryoglobulin-related interference.

Very high IgM concentrations, particularly with cryoglobulin activity, can cause complete CZE failure not resolved by standard dilution or heating. The interference likely involves capillary obstruction from protein aggregation or temperature-dependent re-precipitation within the capillary. BME pretreatment is a critical intervention for unmasking IgM monoclonal proteins when CZE results are inconsistent with other laboratory findings, thereby preventing diagnostic errors.