The free light chain ratio test measures specific proteins in the blood to help identify certain conditions. It assesses the levels of two types of “free” light chains and compares their amounts. This ratio provides insights into the activity of plasma cells, a type of white blood cell involved in the immune system. The test screens for, diagnoses, and monitors disorders involving these plasma cells.
What Are Free Light Chains?
Free light chains are components of immunoglobulins, also known as antibodies, produced by plasma cells. Antibodies are complex proteins the immune system creates to fight infections. Each complete antibody has four protein chains: two “heavy” and two “light” chains.
There are two types of light chains: kappa (κ) and lambda (λ). While most light chains bind to heavy chains to form complete antibodies, plasma cells normally produce a slight excess. These extra, unattached light chains circulate in the bloodstream as “free” light chains. Their presence in low levels is normal.
The Significance of the Ratio
Measuring the ratio of kappa to lambda free light chains is more informative than looking at individual levels. A normal immune response, such as during inflammation or infection, results in an increase in both kappa and lambda free light chains, keeping their ratio within a normal range. This balanced increase suggests generalized immune activation.
An abnormal ratio indicates an imbalance in the production of these two types of light chains. This imbalance points to an overproduction of only one type of light chain by a specific, abnormal group of plasma cells. This clonal expansion produces large amounts of the same type of monoclonal protein, which can be an intact immunoglobulin or just a light chain. The ratio helps identify if a problem stems from a broad immune response or a more specific cellular abnormality.
When the Free Light Chain Ratio Test is Used
The free light chain ratio test detects, diagnoses, and monitors plasma cell disorders, also known as monoclonal gammopathies. This includes multiple myeloma, a cancer originating in plasma cells, and AL amyloidosis, where abnormal proteins accumulate in organs. It is also used for monoclonal gammopathy of undetermined significance (MGUS), a condition that can progress to multiple myeloma.
The test aids initial diagnosis, especially when symptoms like bone pain, fatigue, or kidney problems suggest a plasma cell disorder. It is also valuable for monitoring treatment effectiveness and assessing disease progression. Changes in free light chain levels reflect changes in the size of the abnormal plasma cell population, providing a rapid assessment of treatment response. The free light chain assay is sensitive in detecting light chain diseases and complements other diagnostic tests.
Understanding Your Test Results
When interpreting free light chain ratio test results, healthcare providers consider the levels of both kappa and lambda free light chains, and their calculated ratio. For individuals with normal kidney function, a typical kappa to lambda ratio is approximately 0.26 to 1.65. Normal individual free light chain levels usually range from 3.3 to 19.4 mg/L for kappa and 5.7 to 26.3 mg/L for lambda.
An increased kappa free light chain level with an elevated kappa/lambda ratio may suggest a plasma cell disorder producing excess kappa light chains. Conversely, an increased lambda free light chain level with a decreased kappa/lambda ratio could indicate a disorder producing excess lambda light chains. Kidney dysfunction can also affect free light chain levels, potentially leading to elevated levels of both chains while maintaining a normal ratio, or slightly altering it. Therefore, all test results are interpreted by a healthcare professional in the context of a patient’s overall health, medical history, and other diagnostic findings.