Commentary

Laboratory immunologists have struggled to find ways to monitor disease activity in myeloma patients when densitometric scanning of the abnormal band is not feasible, either because it is hiding within a normal band or for some other reason. Measuring urinary excretion of an associated Bence Jones protein by timed urine collections is cumbersome. Using the serum free light chain ratio holds promise, but it is still a surrogate marker in patients with conventional intact monoclonal gammopathies. Following the “total” immunoglobulin class within which the monoclonal protein falls may be misleading when there are alterations in the concentrations of polyclonal immunoglobulin.

The monoclonal immunoglobulin in this case was not hiding within a normal band but in plain sight! It is not unusual for monoclonal IgA paraproteins to be electrophoretically heterogeneous. After the patient's second remission, the results obtained with her protein electrophoresis and immunofixation samples were interpreted as unremarkable because of the broad span of the monoclonal IgA κ protein. The serum free light chain ratio was not abnormal. Only the total IgA concentration indicated disease progression, which the authors verified by using heavy chain class/light chain type-specific nephelometry reagents to show an abnormal ratio of IgA κ to IgA λ.

By coincidence, I received the invitation to write this commentary on the same day that I received a query about a patient with newly diagnosed myeloma. We had first seen a sample from the patient over a year before and had identified a trace monoclonal IgA hiding within one of the normal β bands. A year later, the overlapping band appeared denser. The question was how to follow this patient's monoclonal IgA, because we could not accurately quantify it by densitometry given its location. In the past, I would have recommended following the total IgA concentration. Now it is clear that we have another alternative for cases like this.

• Received for publication April 27, 2011.
• Accepted for publication May 3, 2011.

• © 2011 The American Association for Clinical Chemistry