Serum free light chains (kappa/lambda ratio)
A blood test that measures the two types of antibody 'light chain' — kappa and lambda — that circulate free in the blood, and reports their ratio. A skewed ratio suggests that a single clone of plasma cells is overproducing one type, which is a clue to myeloma, amyloidosis and related conditions.
What it measures
Antibodies (immunoglobulins) are built from heavy chains and light chains, and the light chains come in two types: kappa and lambda. Normally a small, balanced amount of each circulates free (unattached) in the blood, and the two are produced by a healthy, diverse population of plasma cells — so the kappa-to-lambda ratio sits within a narrow normal range. The test measures each free light chain and, crucially, reports their ratio. Its value is in detecting a clonal plasma-cell disorder: if one abnormal clone of plasma cells multiplies, it pumps out large amounts of just one light chain, tipping the ratio well outside normal. This makes the free light chain assay a sensitive tool for finding and monitoring conditions such as multiple myeloma (including 'light-chain' myeloma that may not show a classic protein band), light-chain amyloidosis, and the pre-cancerous state MGUS. It is more sensitive than older tests for some of these, and the ratio is followed over time to track disease and response to treatment. Reduced kidney function can shift the values, so results are interpreted with kidney function in mind.
What a high value can mean
- An abnormal (skewed) kappa:lambda ratio — the key finding; suggests one clone of plasma cells is overproducing a single light chain.
- Multiple myeloma — including light-chain-only types that may lack a classic protein band.
- Light-chain (AL) amyloidosis — abnormal light chains deposit in organs.
- MGUS — a common pre-cancerous monoclonal state, monitored over time.
- Reduced kidney function — can raise both light chains and shift the ratio, so it is read with kidney function.
High Serum free light chains (kappa/lambda ratio): full guide
What a low value can mean
- A normal ratio — the reassuring result; free light-chain production is balanced.
- A ratio returning toward normal on treatment — can indicate a response in a known plasma-cell disorder.
Low Serum free light chains (kappa/lambda ratio): full guide
When to discuss with a doctor
Free light chains are a specialist test, used mainly to look for and monitor plasma-cell disorders rather than as a general screen. An abnormal ratio, especially alongside anaemia, a high calcium, kidney impairment or a monoclonal protein, prompts a fuller work-up for myeloma or amyloidosis. In someone already diagnosed, the ratio is followed to track the disease and its response to treatment, interpreted by haematology. Because kidney impairment shifts the numbers, the result is always read together with kidney function so it isn't misinterpreted. Mediora.AI surfaces the free light chain ratio alongside immunoglobulins, calcium and kidney function so the plasma-cell pattern is visible; the interpretation and any next steps belong with your haematology team.