A 90-year-old man with hyperphosphatemia.

Hyperphosphatemia is a common condition in patients with decreased kidney function, and without treatment, it can lead to a variety of clinical consequences. However, the presence of hyperphosphatemia in patients with normal kidney function may be true or spurious. We present a case of pseudohyperphosphatemia in a patient with monoclonal gammopathy. An increased paraprotein level can lead to colorimetric interference of the assay of phosphate measurement and result in spurious hyperphosphatemia. The epidemiologic and clinical characteristics of paraprotein-associated pseudohyperphosphatemia also are reviewed here. Ultrafiltration of paraproteins or deproteinization can help correct the measuring error. Patients with spurious hyperphosphatemia should not be treated with phosphate binders. Clinicians treating patients with monoclonal gammopathy should be aware of this relatively common clinical phenomenon and avoid inappropriate treatment of spurious hyperphosphatemia. Copyright Â