Identification of Paraproteins via Serum Immunofixation or Serum Immunosubtraction and Immunoturbidimetric Quantitation of Serum Immunoglobulins in the Laboratory Testing for Monoclonal Gammopathies.

CONTEXT.—: In laboratory testing for monoclonal gammopathies, paraproteins are identified via serum immunofixation or serum immunosubtraction, and immunoturbidimetric quantitation of serum immunoglobulins is often used.

OBJECTIVE.—: To evaluate methodologic differences between serum immunofixation and serum immunosubtraction, as well as in the quantitation of serum immunoglobulins on different clinical chemical platforms.

DESIGN.—: Three hundred twenty-two unique routine patient samples were blinded and used for comparison between serum immunofixation on Sebia's HYDRASIS 2 and serum immunosubtraction on Sebia's CAPILLARYS 2, as well as between quantitation results of immunoglobulin A, G, and M on Abbott's ARCHITECT c16000PLUS and Roche's Cobas c 502 module. Microsoft Excel 2019 with the add-on Abacus 2.0 and MedCalc were used for statistical analysis and graphic depiction via bubble diagram, Passing-Bablok regressions, and Bland-Altman plots.

RESULTS.—: The median age of patients was 75 years, and samples with paraproteinemia were nearly evenly split between sexes. Paraprotein identification differed remarkably between immunofixation and immunosubtraction. Quantitation of serum immunoglobulins showed higher values on Abbott's ARCHITECT c16000PLUS when compared with Roche's Cobas c 502 module.

CONCLUSIONS.—: Identification of paraproteins via serum immunosubtraction is inferior to serum immunofixation, which can have implications on the diagnosis and monitoring of patients with monoclonal gammopathy. If immunoturbidimetric quantitation of immunoglobulins is used for follow-up, the same clinical-chemical platform should be used consistently.