Test Details & Preparation

Serum free light chain (SFLC) testing is ordered to help detect, diagnose, and monitor plasma cell disorders including multiple myeloma and primary amyloidosis, and to monitor the effectiveness of treatment.

Light chains are proteins produced by plasma cells. They are used to assemble immunoglobulins (Ig), antibodies that target and neutralize specific threats to the body such as bacteria and viruses. Two light chains and two heavy chains combine to form an immunoglobulin.

Serum free light chain testing provides complementary information. It can detect the low levels of free light chains that are sometimes all that is produced by a plasma cell disorder and can detect changes in the ratio of kappa and lambda production, which indicate an excess of one clone of plasma cells.

Initially, serum free light chain testing is ordered along with a serum protein electrophoresis test to detect abnormal monoclonal protein (M-protein) production and to calculate a kappa/lambda free light chain ratio. If the protein electrophoresis test is abnormal, then an immunofixation electrophoresis test is performed to determine which immunoglobulin is present in excess. If a plasma disorder is detected, then the free light chain test may be ordered periodically to monitor the condition and to evaluate the effectiveness of treatment.

Serum free light chain testing and a kappa/lambda ratio is ordered along with a protein electrophoresis test when someone has symptoms that a health practitioner suspects are related to a plasma cell disorder. These symptoms will vary from person to person and tend to worsen over time. They involve various parts of the body and may include bone pain, soft spots, anaemia or production of abnormal amounts of light chains can lead to increased light chains in the urine.

A doctor may also order this test when someone has signs and symptoms associated with primary amyloidosis. Amyloidosis develops when abnormal proteins build up in organs or tissue, particularly the heart, liver, kidneys, spleen, gastrointestinal tract, and nervous system. In primary amyloidosis, the proteins are free light chains.

Results of a serum free light chain test will often be evaluated in conjunction with the results of a protein electrophoresis test. Free light chains will normally be present in the blood at low levels, with a kappa/lambda ratio of approximately 0.26 to 1.65. Increased kappa free light chains and an increased kappa/lambda ratio may be seen with plasma cell disorders that produce excess monoclonal kappa light chains. Increased lambda free light chains and a decreased kappa/lambda ratio may be seen with plasma cell disorders that produce excess monoclonal lambda light chains. In general, significantly increased free light chain production and an abnormal kappa/lambda ratio indicate a poorer prognosis and an increased risk of disease progression.