What Does Free Light Chain Ratio Mean?

This page is for people whose blood test report shows a free light chain ratio, often during testing for myeloma or a related condition. It explains what the numbers measure, which thresholds matter, and what to ask.

An antibody is built from heavy chains and light chains. MedlinePlus explains that light chains are "proteins made by plasma cells, a type of white blood cell." Plasma cells normally make a small amount of extra light chains that do not bind to heavy chains. These unlinked chains are free light chains.

Light chains come in two types, kappa and lambda. MedlinePlus says "you will usually have some of each in your blood." The test "measures the amount of lambda and kappa free light chains in your blood." It also gives a ratio comparing the two.

MedlinePlus says that if the amount of free light chains is higher or lower than normal, it may be a sign of a plasma cell disorder. These include multiple myeloma, amyloidosis, MGUS and Waldenstrom macroglobulinemia. The ratio can help diagnose a plasma cell disorder or show how well treatment is working.

Your result usually has three numbers:

• A kappa level.
• A lambda level.
• The kappa/lambda ratio.

NCI writes its rules as the "involved" light chain over the "uninvolved" one. Ask your team which chain is involved in your case, kappa or lambda.

Reference ranges are printed next to the result. Ask your team which range your lab uses. If you switch labs during treatment, tell your oncologist.

MedlinePlus says you may also have a higher level of free light chains if you have a kidney condition. In that case, a higher level may not mean you have a plasma cell disorder. To read your result, your provider will consider your symptoms, medical history and other blood tests, such as kidney tests.

NCI lists an "involved:uninvolved serum free light chain (FLC) ratio of 100 or more" as a myeloma-defining event. NCI lists it with two other findings that can define active myeloma even without organ damage. The three are:

• Clonal bone marrow plasma cells of 60% or more.
• The involved:uninvolved serum FLC ratio of 100 or more.
• More than one focal lesion of at least 5 mm on spine MRI.

NCI also lists four signs of organ damage:

• Calcium more than 1 mg/dL above the lab's reference range.
• Creatinine (a kidney blood test) above 2 mg/dL, or creatinine clearance below 40 mL/min.
• Hemoglobin below 10.0 g/dL.
• One or more bone lesions on x-ray, CT, or PET-CT.

NCI calls these myeloma-defining events. This is why one ratio can change a diagnosis. Your team decides what your own results mean.

NCI defines smoldering myeloma by these findings:

• Serum monoclonal protein (M protein, an abnormal antibody) of the IgG or IgA type of at least 30 g/L, or urinary monoclonal protein of at least 500 mg per 24 hours.
• Clonal bone marrow plasma cells of 10% to 60%.
• None of the myeloma-defining events above.

MGUS, short for monoclonal gammopathy of undetermined significance, is a related condition. NCI lists less than 10% plasma cells in the bone marrow, and no symptoms beyond the M protein.

In smoldering myeloma, NCI says "the FLC ratio of over 100 can predict a greater than 70% progression within 2 years." NCI also describes a "2/20/20" rule. It says three or four adverse factors predict a greater than 50% chance of progression within 2 years. One of the factors is an FLC ratio of more than 20. Two people with the same label can have different follow-up plans.

NCI says quantitative free light chains may help follow response when an M protein is not apparent. NCI also lists other tests for people with an M protein:

• Serum M protein by electrophoresis.
• Urine M protein over 24 hours.
• Immunofixation electrophoresis to identify the heavy and light chain.
• Blood counts, marrow plasma cell percentage, and kidney tests.

MedlinePlus says a free light chains test is often ordered with an immunofixation blood test to help confirm or rule out a diagnosis.

MedlinePlus lists possible symptoms of a plasma cell disorder. They include bone pain, fractures, weakness, numbness or tingling in the arms or legs, fatigue, frequent infections and fevers, easy bruising or bleeding, trouble breathing, feeling very thirsty, and frequent urination.

• Call 911 or go to the nearest emergency department for sudden confusion or being hard to wake, sudden severe trouble breathing, black or tarry stool, blood in vomit or vomit that looks like coffee grounds, substantial bleeding, or sudden complete inability to urinate.
• If you are on treatment, call your care team right away, day or night, for a temperature of 100.4°F (38°C) or higher, chills, sore throat, mouth sores, burning when you urinate, or any other sign of infection, even without a fever.
• Call your care team the same day for new bone pain or a fracture, new weakness, numbness or tingling, or easy bruising or bleeding.

• Which chain is involved, kappa or lambda?
• What is my exact ratio, and what range does this lab use?
• Was my creatinine drawn the same day? Could kidney function explain part of this?
• Am I above or below a ratio of 100, and does that change my category?
• Is a bone marrow biopsy, an immunofixation, or a bone survey still pending?
• How often will this be repeated?

See also Pathology Reports, Cancer Staging, and Biomarker Testing and Precision Medicine.

• https://medlineplus.gov/lab-tests/free-light-chains/.
• https://www.cancer.gov/types/myeloma/hp/myeloma-treatment-pdq.