Immunoglobulin Measurements

Serum protein electrophoresis is required for detecting monoclonal Ig. Cellulose acetate or agarose gel elec-trophoresis is commonly used. The latter was shown to be more sensitive.110 A monoclonal immunoglobulin (M spike) is identified as a discrete, homogeneous band on electrophoresis or as spikes in the 7, p, or a2 region of the densitometer tracing. Two M proteins may occur rarely (biclonal gammopathy). Immunofixation is then used to determine the isotype of the paraprotein, using specific antibodies to 7, a, 8, and/or e heavy-chain isotypes and to k and X light-chain isotypes. Typing for IgD and IgE is not routinely done and should be requested when IgD or IgE myeloma is suspected.

Urinary protein electrophoresis should be performed on an 80-100 X concentrated random sample. Immunofixation electrophoresis more sensitive for detecting proteins in low concentration, should also be performed. If monoclonal free light chain is identified, a 24-h urine collection should be sent for quantifying daily excretion of light chain and other proteins, especially albumin. The urine dipstick is not sensitive to Bence Jones protein. Urinary light chains that occasionally form multiple, equally spaced bands ("ladder pattern") are generally polyclonal.111

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