What is a free light chains test?

A free light chains test measures the level of free light chains in your blood. Light chains are proteins made by plasma cells, a type of white blood cell. Light chains usually link up with other proteins called heavy chains. Together, the light and heavy chains make immunoglobulins, also called antibodies. Antibodies are proteins that your immune system makes to fight germs such as viruses and bacteria.

Light chains can be bound or free:

• When light chains link up with heavy chains, they are known as bound light chains.
• Normally, your plasma cells will make a small amount of extra light chains that don't bind with heavy chains. Instead, they are put into your bloodstream. These unlinked chains are known as free light chains.

There are two types of light chains: lambda and kappa light chains. You will usually have some of each in your blood. A free light chains test measures the amount of lambda and kappa free light chains in your blood.

If the amount of free light chains is higher or lower than normal, it may be a sign of a disorder of the plasma cells. These disorders include multiple myeloma, a cancer that begins in the plasma cells, and amyloidosis, a condition that occurs when abnormal proteins build up and collect in different organs and tissues.

Other names: free kappa/lambda ratio, kappa/lambda quantitative free light, freelite, kappa and lambda free light chains, immunoglobulin free light chains, free light chain assay test

What is it used for?

A free light chains test is used to measure the level of free light chains in the blood and compare the amount of kappa and lambda light chains. This ratio can help diagnose or monitor how well the treatment of plasma cell disorders is working.

Why do I need a free light chains test?

Your health care provider may order this test if you have symptoms of a plasma cell disorder. Depending on which plasma disorder you may have and which organs are affected, your symptoms may include:

• Bone pain, often in the back or ribs
• Fractures (broken bones)
• Weakness, numbness, or tingling in the arms or legs
• Fatigue
• Frequent infections and fevers
• Easy bruising or bleeding
• Trouble breathing
• Feeling very thirsty
• Frequent urination
• Tongue swelling
• Purple spots on the skin

What happens during a free light chains test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a free light chains test.

Are there any risks to a free light chains test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your results will show the amounts of lambda and kappa free light chains in your blood. It will also provide a comparison between the two, called a ratio.

If your results were not normal, it may be a sign of a plasma cell disorder, such as:

• Multiple myeloma.
• Amyloidosis.
• MGUS (monoclonal gammopathy of unknown significance). This is a condition in which you have abnormal protein levels. It often has no symptoms but sometimes can become multiple myeloma.
• Waldenstrom macroglobulinemia (WM), a cancer of the white blood cells. It's a type of non-Hodgkin lymphoma.

You may also have a higher level of free light chains if you have a kidney condition. In this case, a higher level may not mean that you have a plasma cell disorder.

To understand the results of a free light chains test, your provider will consider your symptoms, medical history, and the results of other blood tests.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a free light chains test?

A free light chains test is often ordered with other tests, including an immunofixation blood test, to help confirm or rule out a diagnosis.