The analytical sensitivity of SPE, CZE and other routine laboratory tests for monoclonal immunoglobulin detection is summarised in Table 4.1. In practice, the detection limit of electrophoretic techniques is dependent on a number of factors including: 1) the position of the monoclonal protein; 2) the level of polyclonal background immunoglobulins (in the γ-region); and 3) the width of the monoclonal protein peak [127]. Not all monoclonal proteins can be accurately quantified by SPE due to co-migration or dye saturation issues (Section 17.4).
When the diagnostic sensitivity of CZE and SPE is compared with that of sIFE, both methods fail to detect a small percentage of monoclonal proteins (Table 4.2). A high proportion of these samples are monoclonal IgA, IgM or sFLCs [126]. Such monoclonal proteins represent a diagnostic challenge as they may be small and co-migrate with other serum protein peaks, making detection and accurate quantification challenging (Section 17.4). In some cases, an abnormal κ/λ sFLC ratio may prompt sIFE to be performed, and reveal the presence of a hidden monoclonal intact immunoglobulin (Chapter 13) [129]. The diagnostic specificity of SPE and CZE are similar, although the reported values are variable between different studies (Table 4.2).
| SPE | CZE | |||
|---|---|---|---|---|
| Study | Diagnostic sensitivity (%) | Diagnostic specificity (%) | Diagnostic sensitivity (%) | Diagnostic specificity (%) |
| Bossuyt 1998[130] | 86.0 | Not reported | 93.0 | Not reported |
| Katzmann 1998 [123] | 90.7 | 98.9 | 94.9 | 98.6 |
| Poisson 2012 [124] | 89.9 | 75.4 | 97.4 (or 92.3)* | 57.6 (or 72.2)* |
| Yang 2007 [126] | 90.0 | 100 | 81 | 100 |
Table 4.2. Comparison of the diagnostic sensitivity of SPE and CZE to detect monoclonal proteins identified by sIFE. * Values refer to Sebia CAPILLARYSTM2 (or Helena V8TM) instruments.
