Pseudohyperphosphataemia in patients with multiple myeloma.

The phosphate concentrations were measured in 41 patients who had multiple myeloma with paraproteinaemia using four different methods to compare the incidence of pseudohyperphosphataemia. The direct acid/molybdate method produced the highest number of anomalous results. The erroneously high phosphate concentration was attributable to the presence of turbidity in the reaction mixture. No association was found between paraprotein type and occurrence of turbidity. The direct acid/molybdate method was unreliable in patients with serum paraproteins and should therefore not be used for the measurement of phosphate concentration in such patients.