Reporting Apparent Biclonal Immunoglobulin-A Monoclonal Proteins with Identical Light Chains

It is generally not well appreciated that Immunoglobulin A (IgA) can present as apparent biclonal monoclonal protein (M-protein) comprising monomers and polymers, despite the fact that Kyle pointed this out in 1999. In this clinical communication, we report on 3 patients with Ig-A multiple myeloma (MM) who displayed this phenomenon. Of these 3 patients, 2 had identical kappa light chains suggesting biclonality, while the other had 2 lambda light chains. Because the Ig-A M-proteins are clustered in the beta-area, accurate densitometric quantification is made difficult. Hence, we suggest assaying Ig-A levels and free light chains in concert with the M-protein levels to monitor these patients on therapy. In conclusion, when encountering biclonal Ig-A M-proteins with identical light chains, the laboratorian should add the 2 values and present one composite number to the clinician.