MULTIPLE MYELOMA KNOWLEDGE CENTER

Free Light Chain Assays

Free light chain assays measure the amount of light chains in the blood. Light chains, known specifically as immunoglobulin light chains, are small molecules found in antibodies. Analyzing light chains help diagnose rare cases of myeloma in which no myeloma protein is found in other blood tests.

Serum free light chain assays are best performed on blood fluid (serum) rather than urine because of the kidneys’ filtering effects. Kidneys prevent protein loss from the body into the urine. Therefore, elevated M-protein levels may be identified in the blood before it is identified in the urine. Serum free light chain assays are so effective in the initial diagnosis of myeloma that urine tests are no longer required.

While serum free light chain assays are excellent for detection of free light chains, these tests are unable to detect whole immunoglobulins. Doctors will therefore perform electrophoresis to evaluate immunoglobulins levels, and will also perform serum free light chain assays to evaluate free light chain levels.

Free light chain assays also help doctors evaluate a patient’s response to treatment in a matter of hours to days, whereas it may take up to three weeks to detect response using other tests such as serum protein electrophoresis.