Immunoglobulin Heavy/Light Chain Ratios as An Alternative to Immunofixation In the Identification of Monoclonal Gammopathies

Historically, serum protein electrophoresis (SPE), urine protein electrophoresis (UPE) and immunofixation (IFE) have been used to identify and quantify monoclonal proteins (M-proteins). Whilst this approach is adequate for the identification of intact immunoglobulin multiple myeloma (MM), it is not sensitive enough to detect free light chain MM (LCMM). Therefore, an algorithm which utilises SPE, serum free light chain (FLC) immunoassays and IFE for the identification of M-proteins has been suggested. Assays have now been developed which utilise polyclonal antisera raised against the kappa and lambda light chain types of IgG, IgA and IgM immunoglobulins (HLC). Here we report the use of these assays as an alternative to IFE and propose a screening algorithm which utilises SPE, FLC and HLC

Serum FLC measurement was added to 1063 requests for SPE, from primary care or from a hospital source. Samples from patients with previously diagnosed MM, Waldenstrom's Macroglobulinemia and lymphoma were, where possible, removed. Sera showing monoclonal proteins or hypogammaglobulinemia (by SPE) or an abnormal FLC ratio were tested further by IFE and IgG, IgA, IgM HLC assays. SPE and IFE were performed on a SEBIA Hydrasys system, and gels were interpreted by experienced clinical chemists. FLC and HLC measurements were performed on a Siemens BN™II nephelometer. HLC results were compared with IFE results and clinical diagnoses. The study was approved by the Wolverhampton, New Cross, NHS Trust Review Board

80/1063 patients were identified as having abnormal SPE or abnormal FLC results. 42/80 patients had positive IFE results. 24/42 of these patients were positive by HLC (Table 1), 11/42 had light chain only myeloma/MGUS, the remaining 7/42 were MGUS patients. The 7 MGUS patients (6 IgG and 1 IgM) with normal HLC ratios and positive IFE all had less than 2g/L monoclonal protein measured by SPE densitometry and a normal FLC ratio. Of the 38/80 with normal IFE's all had been investigated further because of abnormal FLC results. 9/38 had abnormal HLC ratios of which 3/9 had confirmed hematological malignancies (1× chronic lymphocytic leukemia (CLL), 1× small lymphocytic lymphoma (SLL) and 1× asymptomatic MM (ASMM)).

The use of FLC immunoassays alongside SPE as part of the primary screening protocol identified 10 additional hematological malignancies (1× ASMM, 6×CLL, 2× non-Hodgkin lymphoma, 1× SLL).

HLC ratio analysis matched IFE for the identification of all symptomatic haematological malignancies. Abnormal FLC ratios identified 10 additional haematological malignancies of which 3 also had abnormal HLC ratios, which would have been missed using SPE/ IFE. In 7/19 MGUS (6×IgG, 1×IgM) patients there were normal HLC ratios. In all cases the monoclonal protein load was below 2g/L and the FLC ratio was normal; identifying the IgG patients as having a low risk and the IgM patient as having a low/intermediate risk of progression. It may be beneficial not to identify these patients, who do not require therapeutic intervention or justify close monitoring. Another advantage of using HLC analysis instead of IFE is that the HLC ratio has been found to be a prognostic indicator in myeloma and MGUS. It would also form a useful “baseline” comparison if HLC assays were used in monitoring or for the detection of residual disease.

HLC analysis identified all symptomatic patients who were IFE positive and in an additional 3 hematological malignancies. Low risk MGUS patients may not be identified using these tests but this might be beneficial to patients and physicians alike

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