The cloned cancerous plasma cells in the bone marrow will produce light chains in the blood. They are typically either all Kappa or all Lambda. These light chains bind to a heavy chain to create an immunoglobulin. When there is an excessive amount of light chains and there are not enough heavy chains the bind to, then they are called free light chains. The ratio is simply the ratio between free Kappa and free Lambda light chains. A large number means you have more than one over the other.
So this is a way to estimate if you have MM and if it is progressing or receding. You are monitoring the effects, not necessary the cause.
When the light chains do successfully bind to a heavy chain they create a Immunoglobulin. The types are typically IgG, IgA and IgM. These can also be measured with the Serum Quantum Immunoglobulin blood test. Typically you might see one type of Ig with a very large value.
So as an example, my MM does not produce free light chains. But is does produce IgA Ig's.
Hope this helps,
Mark

My understanding is your body produces Kappa and Lambda free light chains. They can increase due to other conditions in the body but they increase together. When only one increases dramatically over the other you are looking at Free Light Chain Myeloma which is why they are interested in the ratio of the two. If the Kappa increases and the lambda stays low you have free light chain kappa, which is what I have. If the Lambda increases and the kappa stays low you have free light chain lambda which I understand to be less common and harder to treat. This type of myeloma also has a byproduct that can clog up the tiny filters in the kidneys which is why it usually damages the kidneys rapidly. My ratio at diagnoses was around 15,000 and my kidney numbers were to the point of indicating dialysis might be needed.. Fortunately when they took me off of medicine that was hard on my kidneys and I started drinking enormous amounts of fluids and cut out almost all salt my kidney numbers recovered over a 6 weeks time frame. I am on maintenance now post SCT with lenalidimide, which is hard on the kidneys, so my doctor watches my kidney numbers along with my kappa/lambda ratio as well as protein numbers.

I know that my myeloma produces both Kappa and Lambda light chains, but the Kappa far outnumber the Lambda. I seem to remember a "definition" of Kappa light chain myeloma that said the Kappa/Lambda ratio had to be above a certain number. I'm wanting to say it was 100 to one, but I'm not sure. Based on that ratio, whatever it was, I decided at the time that I did not have Kappa light chain myeloma.
Again, I will ask my doctor next time I visit his office, near the end of this month. He told me when I was diagnosed that I have a high risk form of myeloma; but he did not say that it was Kappa light chain myeloma.
Interesting thing: the only organs that were affected at rhe time of diagnosis were the kidneys; but they were still functioning at 90% effeciency.