Evaluation of IgG, IgA and IgM monoclonal and biclonal gammopathies by nephelometric measurement of individual immunoglobulin κ/λ ratios – Hevylite assay versus immunofixation

Immunofixation is a standard method for detecting monoclonal immunoglobulins and characterizing its isotype. Recently clonality can also be determined by using immunoglobulin heavy chain /light chain immunoassays – “Hevylite” HLC. Availability of antibodies which bind to conformational epitopes spanning the junctional regions between bound κ or λ light chains and their respective heavy chain partners has allowed the specific measurement of serum IgGκ, IgGλ, IgAκ, IgAλ IgMκ and IgMλ concentrations. In turn, this has enabled the calculation of IgGκ/IgGλ, IgAκ/IgAλ and IgMκ /IgMλ ratios (heavy/light chain or HLC ratios) for individual patients. In this study, the diagnostic value of HLC ratios was compared with the serum protein immunofixation (IFE) results. Sera from 51 patients with monoclonal and biclonal gammopathy including 34 with multiple myeloma and 11 with Waldenström’s macroglobulinemia were assayed. IFE and HLC ratio results were concordant for 44 of the 51 IFE – monoclonal protein positive samples. IFE detected 2 “minor” IgGκ bands (1oligoclonal in multiple myeloma patient in CR after ASCT, 1 in Hodgkin lymphoma patient in 10 year CR), and 1 IgAλ with polyclonal background (in a patient with multiple myeloma and liver cirrhosis) that were not detected by HLC assay. In 6 cases with biclonal IgGκ + IgGλ gammopathy revealed in IFE, the HLC ratios were normal in 3, also in the three cases the HLC ratios revealed only one component IgGκ or IgGλ. In 4 cases with biclonal IgG + IgA gammopathy, including 3IgGκ + IgAκ cases and one IgGκ + IgAλ, the HLC ratios were concordant with IFE. In one patient with Waldenström’s macroglobulinemia and 3 homogenous bands IgG+IgA+ IgM in serum IFE analysis, the HLC assay correctly revealed only IgMκ/IgMλ abnormal ratio while IgGκ/IgGλ and IgAκ/IgAλ ratios were normal, as has been also proved in quantitative studies of total immunoglobulin concentration. Our results indicate that HLC and IFE are complementary methods. HLC assay provides numerical results. There is raised the question of HLC predictive value. A carried out in our study evaluation of survival of 21 patients with IgM monoclonal gammopathy diagnosed with multiple myeloma or Waldenström macroglobulinemia whose average time of observation was 6 years showed a median survival time of 7 years in patients with the values of HLC ratios < the median and 5.5 years in patients with values of HLC ratios> the median.