Elevated immunoglobulin K light chain in urine is usually caused by plasma cell disease. Plasma cells are cells in the body that produce immunoglobulins and the components that make up immunoglobulins include heavy and light chains, which are usually produced and assembled in a certain ratio to form immunoglobulins. If the synthesis of heavy chains and light chains is disproportionate, an increase in the synthesis of light chains will be detected in the urine after glomerular filtration, and K light chains are one of them. This light chain can not only be filtered through the glomerulus, but also deposited into the kidney and cause kidney damage. At this point, it should be identified if it is monoclonal, if not it can be monitored closely, if it is monoclonal, it may suggest plasma cell disease. The prognosis of this disease is relatively poor and usually requires treatment with hormones and mafalonium.