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[False hyperphosphoremia in multiple myeloma. Interference of monoclonal immunoglobulin G with the determination of
B Lorcerie1, J F Besancenot, F Maillefert
1Service de Médecine Interne et Immunologie Clinique, CHU, Dijon.
Abstract:
A case of pseudohyperphosphataemia detected in a male patient with multiple IgG myeloma is reported. Phosphataemia, measured by a technique without previous deproteinization, reached 5.66 mM before any treatment and varied with treatment-induced changes in monoclonal immunoglobulin levels. Conversely, normal phosphataemia levels were found in blood samples taken before and after treatment when serum was deproteinized. This pseudohyperphosphataemia resulted from an increase in optic density due to interference between monoclonal immunoglobulin and the molybdic reagent used to determine phosphataemia. A retrospective investigation yielded three similar cases: two in patients with myeloma and one in a patient with non-myelomatous monoclonal dysglobulinaemia. A brief prospective study showed that this phenomenon was relatively frequent, as it was found in 2 out of 9 patients with monoclonal immunoglobulin (IgG in all 9 cases). These data indicate that the finding of marked hyperphosphataemia in subjects with monoclonal dysglobulinaemia should always prompt a control assay performed on deproteinized blood.
Insights
Pseudohyperphosphatemia can occur in patients with monoclonal gammopathies like IgG myeloma. This occurs due to lab assay interference, not actual high phosphate levels, requiring deproteinization for accurate results.
Area of Science:
- Clinical Chemistry
- Hematology
- Immunology
Background:
- Monoclonal gammopathies, including multiple IgG myeloma, are characterized by the overproduction of a single type of immunoglobulin.
- Accurate biochemical measurements are crucial for diagnosis, monitoring, and management of these conditions.
- Standard laboratory assays may be subject to interference from abnormal proteins.
Observation:
- A case of pseudohyperphosphatemia was observed in a male patient with multiple IgG myeloma.
- Elevated serum phosphate levels, measured without deproteinization, correlated with monoclonal immunoglobulin levels.
- Deproteinization of serum samples yielded normal phosphate levels, indicating a non-true elevation.
Findings:
- The pseudohyperphosphatemia was attributed to interference between monoclonal immunoglobulin and the molybdic reagent used in the phosphate assay.
- Retrospective and prospective studies identified this phenomenon in other patients with monoclonal gammopathies, including myeloma and monoclonal dysglobulinemia.
- The incidence was found to be relatively frequent in patients with monoclonal immunoglobulin (2 out of 9 IgG cases).
Implications:
- The presence of marked hyperphosphatemia in patients with monoclonal dysglobulinemia should prompt a confirmatory assay on deproteinized blood.
- This finding highlights the importance of recognizing and accounting for analytical interferences in laboratory diagnostics for patients with monoclonal gammopathies.
- Clinical laboratories should be aware of potential interferences from monoclonal immunoglobulins in various biochemical assays.