Chapter 17

Total immunoglobulin measurements are unable to distinguish monoclonal from polyclonal immunoglobulin concentrations of the same isotype. Therefore, when IIMM patient samples contain significant concentrations of non-tumour polyclonal immunoglobulins, nephelometric results are inaccurate.

Nephelometry is also known to grossly overestimate monoclonal IgM concentrations. In one study, IgM values obtained by SPE and nephelometry were linearly correlated with a slope of 1.8 (CI 1.68 – 1.92), showing a systematic bias for higher values by nephelometry [369].