I guess this is something I have. It's called MGUS. Gosh I forgot what the MGUS stands for, but the test for it is that light chain business. My hematologist gave this test to me six or more years ago, simply testing out a spectrum of diseases. I already had been dx'd with Polycythemia Vera, a myeloproliferative disease. I was positive for MGUS as well.

In its early stages, MGUS has no symptoms. And it may never turn into Multiple Myeloma. It is much more common among the general population than are my other illnesses. In fact, my pcp who just left the area with her family to work in another state, has MGUS. She too, is in an early non-symptomatic state, which may never turn into Multiple Myeloma. If the disease does turn into MM, it is serious. Tumors begin to form in various places. I probably could not tolerate the chemotherapy for it, so I am hoping I will not advance into that during my life.
I am tested yearly to see if the illness has advanced, and it has not. In fact, my scores were lower this year. Nothing going on. Thank God.

I googled compete name for MGUS: Monoglonal Gammopathy of Unknown Origin