Pseudohyperphosphatemia induced by endogenous lipoproteins: New elements supporting an interference with ammonium phosphomolybdate-based methods

BackgroundInorganic phosphate (Pi) is a crucial electrolyte for maintaining homeostasis. Most methods measure Pi using ammonium phosphomolybdate under highly acidic conditions. Phospholipid-rich substances, such as liposomal amphotericin B, have been previously reported to artificially elevate Pi levels due to phospholipid hydrolysis in the acidic medium. This study aimed to investigate whether endogenous lipoproteins interfere with Pi measurement in cases of hyperlipidemia.MethodsWe conducted a retrospective study comparing mean Pi levels in 194,636 patients divided in groups with varying degrees of lipemia. Additionally, we performed a prospective study involving 85 patients presenting a range of lipemia to evaluate changes in Pi levels before and after plasma high-speed centrifugation-filtration, which retains all endogenous lipoproteins.ResultsThe retrospective study revealed a significant increase in Pi levels in relation with the degree of lipemia (<i>P</i> < .0001). The prospective study demonstrated a significant decrease in phosphatemia (<i>P</i> < .0001), with mean Pi levels of 1.36 mmol/L (4.22 mg/dL) before filtration and 1.27 mmol/L (3.94 mg/dL) after filtration, representing a mean decrease of 6.8%. Furthermore, the bias, defined as 100*(([Pi]_before - [Pi]_after)/[Pi]_before), was correlated with the lipemia level (r = 0.34, <i>P</i> = .001).ConclusionsThis study confirms that hyperlipidemia induces an analytically significant pseudohyperphosphatemia in a lipemia-dependent manner.