The Free Light Chains test is a blood test that measures the levels of two types of proteins, called kappa and lambda, in the blood. These proteins are produced by plasma cells in the bone marrow and play a role in the immune system’s response to infection and disease. When plasma cells become cancerous and begin to grow uncontrollably, they can produce an excess of free light chains, which can lead to multiple myeloma or other types of plasma cell disorders. The Free Light Chains test is commonly used to diagnose and monitor these conditions. The test can also be used to monitor the effectiveness of treatment or to detect relapses. The test is done by drawing a blood sample from a vein and is a simple and relatively non-invasive procedure. Abnormal levels of free light chains can indicate the presence of a plasma cell disorder and may require further testing or treatment.