Pseudohyperphosphatemia in a hyperphosphatemic hemodialysis patient.

Hyperphosphatemia is a predictable consequence of end-stage renal disease. Pseudohyperphosphatemia is a spurious elevation of serum phosphate in samples containing a substance that interferes with the laboratory assay for phosphate. The most common cause is a paraprotein in disorders such as Waldenström's macroglobulinemia and multiple myeloma. We report here a case of pseudohyperphosphatemia in a hyperphosphatemic patient with end-stage renal disease on long-term hemodialysis caused by a saline solution containing phosphorus used to dilute the patient's serum sample in the clinical chemistry laboratory. Investigations showed that the phosphorus most likely was introduced at the time of saline manufacture. Pseudohyperphosphatemia resulting from the manufacture and distribution of saline-containing phosphorus could be a cause of abnormally high serum phosphate measurements in hyperphosphatemic dialysis patients whose serum samples must be diluted in the laboratory. Such spuriously elevated results can lead to inappropriate changes in medications and subject patients to additional hemodialysis treatments.