Paraproteins are abnormal monoclonal immunoglobulins produced in plasma cell disorders (eg multiple myeloma), lymphoproliferative disorders (eg CLL, Waldenstrom’s macroglobulinaemia) and in some infections (hepatitis C).

The introduction of the assay, serum free light chains (FLC) has meant the initial investigation of paraproteinaemia has become much simpler.

Previously, serum tests had great difficulty in detecting immunoglobulin light chains for two reasons:

1. Light chains are rapidly cleared by the kidneys, up until a certain point where they ‘spilled’ over into the blood.
2. Assays had poor sensitivity in detecting ‘free’ light chains ie light chains not bound to heavy chains as in normal immunoglobulin.