Abstract
Background
Multiple myeloma patients may present with spuriously elevated serum phosphate levels resulting from the presence of paraproteins interfering in the phosphomolybdate UV assay. If this phenomenon is not recognized, patients possibly receive unnecessary treatments. This short report highlights the existence of paraprotein-related pseudohyperphosphatemia, and aims to provide accessible solutions to eliminate this interference.
Material and Methods
In a patient known with IgG multiple myeloma and unexplained hyperphosphatemia, the correlation between serum phosphate levels (phosphomolybdate UV assay) and IgG concentrations (immunoturbidimetry) was evaluated. To investigate the effect of the paraprotein on phosphate levels, phosphate was measured in one serum sample before and after protein removal by either dilution, protein precipitation with sulfosalicylic acid or zinc sulphate, or ultrafiltration.
Results
A patient with multiple myeloma presented with an unexplained hyperphosphatemia which correlated positively with serum IgG concentrations. As serum dilution normalized the phosphate level, it was hypothesized that precipitation of the paraprotein during the assay reaction interfered with the measurement and resulted in pseudohyperphosphatemia. Protein removal by precipitation with sulfosalicylic acid or zinc sulphate efficiently reduced the IgG level below the detection limit but did not result in a reliable phosphate measurement. Successful removal of proteins and a serum phosphate level that matched the patient’s other biochemistry parameters and clinical condition were obtained by ultrafiltration.
Conclusion
Paraproteins can interfere with the reaction components in the phosphomolybdate UV assay and result in pseudohyperphosphatemia. If the presence of this phenomenon is established, a reliable phosphate concentration can be obtained after ultrafiltration of the sample.
Keywords
Get full access to this article
View all access options for this article.
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
