Abstract
Kidney involvement in multiple myeloma can result in kidney failure. Unlike Waldenström macroglobulinemia, hyperviscosity syndrome is a rare occurrence in multiple myeloma. Timely detection of hyperviscosity syndrome and initiation of plasma exchange to remove paraproteins can significantly alter the clinical course and be potentially lifesaving. We report a case of hospitalized patient with kidney failure due to multiple myeloma not in remission who experienced shortened hemodialysis sessions due to early dialysis filter failure due to hyperviscosity, which was later corrected with plasmapheresis. When confirmation of high levels of serum free light chains (sFLCs) was attempted, sFLC was initially reported as "not detectable." This false-negative result reflected a laboratory artifact caused by a high abundance of sFLCs, known as antigen excess or hook phenomenon. Manual serial dilutions led to unmasking of markedly elevated κ light chain levels. This case exemplifies that patients with multiple myeloma can exhibit clinically challenging kidney manifestations even after becoming dialysis dependent.