Pseudohyperphosphatemia induced by endogenous lipoproteins: New elements supporting an interference with ammonium
Charles R Lefèvre1,2, Felipe Le Divenah1, Bastien Paterek1
1Clinical Biochemistry and Toxicology Laboratory, Rennes University Hospital Centre, Rennes, France.
Abstract:
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 (P < .0001). The prospective study demonstrated a significant decrease in phosphatemia (P < .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, P = .001).ConclusionsThis study confirms that hyperlipidemia induces an analytically significant pseudohyperphosphatemia in a lipemia-dependent manner.
Insights
Hyperlipidemia can falsely elevate inorganic phosphate (Pi) levels, a condition known as pseudohyperphosphatemia. This study confirms this interference is dependent on lipemia levels.
Area of Science:
- Clinical Chemistry
- Biochemistry
- Medical Diagnostics
Background:
- Inorganic phosphate (Pi) is vital for homeostasis.
- Standard Pi measurement methods use acidic conditions, which can interfere with certain substances.
- Previous studies noted phospholipid interference; this study investigates endogenous lipoproteins.
Purpose of the Study:
- To determine if endogenous lipoproteins in hyperlipidemia interfere with inorganic phosphate (Pi) measurement.
- To quantify the impact of lipemia on Pi levels.
Main Methods:
- Retrospective analysis of Pi levels in 194,636 patients across varying lipemia degrees.
- Prospective study of 85 patients evaluating Pi levels before and after plasma filtration to remove lipoproteins.
Main Results:
- Retrospective data showed a significant Pi increase with higher lipemia (P < .0001).
- Prospective study: Pi levels decreased by 6.8% after filtration (1.36 vs. 1.27 mmol/L, P < .0001).
- The bias in Pi measurement correlated with lipemia levels (r = 0.34, P = .001).
Conclusions:
- Hyperlipidemia causes analytically significant pseudohyperphosphatemia.
- The degree of lipemia directly influences the accuracy of Pi measurements.
- This interference must be considered in clinical diagnostics for hyperlipidemic patients.
