title: Spuriously elevated inorganic phosphate level in a multiple myeloma patient.
abstract: We report the case of a patient with IgG multiple myeloma and pseudohyperphosphatemia. The patient had no clinical features of hyperphosphatemia. Subsequent investigations demonstrated that this hyperphosphatemia was spurious and was caused by a high concentration of the paraprotein. Deproteinization of the serum samples by sulfosalicylic acid resulted in normalization of the elevated phosphate values. This pseudohyperphosphatemia resulted from an increase in optic density because of interference between monoclonal immunoglobulin and the molybdic reagent used to determine phosphate in serum. These data indicate that the finding of marked hyperphosphatemia in multiple myeloma patients should always prompt an assay carried out on a deproteinized sample. In addition, knowledge of this phenomenon may avoid confusion, unnecessary testing and obviate confusion in the clinical evaluation of patients with multiple myeloma.
authors.affiliation: Department of Clinical Biochemistry, Ege University Faculty of Medicine, Izmir, Turkey.
authors.forename: B
authors.initials: B
authors.lastname: Barutçuoglu
authors.forename: Z
authors.initials: Z
authors.lastname: Parildar
authors.forename: I
authors.initials: I
authors.lastname: Mutaf
authors.forename: S
authors.initials: S
authors.lastname: Habif
authors.forename: O
authors.initials: O
authors.lastname: Bayindir
mesh_terms: D011232:Chemical Precipitation; D005189:False Positive Reactions; D017809:Fatal Outcome; D006801:Humans; D007145:Immunoglobulin kappa-Chains / Q000032:analysis*; D007202:Indicators and Reagents; D008297:Male; D008875:Middle Aged; D008982:Molybdenum / Q000737:chemistry; D009101:Multiple Myeloma / Q000097:blood*; D009194:Myeloma Proteins / Q000032:analysis*; D010710:Phosphates / Q000097:blood*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D007145:Immunoglobulin kappa-Chains; D007202:Indicators and Reagents; D009194:Myeloma Proteins; D010710:Phosphates; D008982:Molybdenum; C022175:ammonium molybdate