Kappa free light chains

3.3 to 19.4 mg/L is the range for the most widely used UK method (Freelite); other methods print different ranges. Both light chains rise with reduced kidney function in the general population, and the ratio is then read against a wider range.

Antibodies are built from two heavy chains and two light chains, and the light chains come in two types, kappa and lambda. The cells that make antibodies always produce a small surplus of light chains, which float free in the blood and are cleared by the kidneys. This test measures the free kappa chains. It is always read together with the free lambda chains and the ratio of the two.

Doctors request the free light chains, together with serum protein electrophoresis, when looking at myeloma and related conditions, in unexplained kidney disease, bone pain, anaemia or a high ESR, and to follow people with a known light chain condition over time.

• Reduced kidney function, which raises both kappa and lambda together
• Myeloma and related conditions that make kappa light chains, where kappa rises alone
• Inflammation, infection and autoimmune conditions, which raise both together
• Older age, a little, in the general population

• Myeloma and related conditions that make lambda light chains, where kappa is suppressed
• Immune-suppressing medicines and chemotherapy
• Treatment of a kappa light chain condition

• Reduced kidney function raises both light chains together without any blood condition; the ratio is what matters then
• Any inflammation or infection raises both together
• Methods differ, so numbers from two laboratories using different methods are not comparable

No fasting needed. Always read alongside the lambda light chains and the kappa/lambda ratio from the same sample, and with kidney function. In people with a known condition the trend over time matters more than one value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.