Interferences in the measurement of circulating phosphate : A literature review

Inorganic phosphate in blood is currently determined by the reaction with molybdate. This report aims at reviewing conditions underlying spuriously altered levels of circulating inorganic phosphate. A systematic search of the Excerpta Medica, the National Library Database and the Web of Science database was conducted without language restriction from the earliest publication date available through January 31, 2020. For the analysis, 80 reports published in English (n = 77), French (n = 1), German (n = 1) and Spanish (n = 1) were retained. Well-documented pseudohyperphosphatemia was observed in individuals exposed to liposomal amphotericin, in patients affected by a gammopathy, in patients with hyperlipidemia and in patients with hyperbilirubinemia. An unexplained elevated inorganic phosphate level sometimes provided a clue to the diagnosis of a gammopathy. Well-documented cases of pseudohypophosphatemia were observed in patients on large amounts of intravenous mannitol. Finally, pseudohypophosphatemia was occasionally observed on treatment with liposomal amphotericin and in patients with a gammopathy. In order to avoid unnecessary testing and treatment, the phenomenon of spuriously altered inorganic phosphate should be recognized. An unexplained hyperphosphatemia may provide a clue to the diagnosis of a gammopathy or a severe hyperlipidemia.