Pseudohyperphosphataemia in multiple myeloma

Area of Science:

• Clinical Chemistry
• Hematology
• Oncology

Background:

• Hyperphosphataemia is a common clinical finding.
• Multiple myeloma is a hematologic malignancy characterized by abnormal plasma cells.
• Accurate biochemical measurements are crucial for patient management.

Purpose of the Study:

• To report two cases of spurious hyperphosphataemia in multiple myeloma patients.
• To identify the cause of falsely elevated phosphate levels.
• To raise awareness of potential laboratory interference in myeloma.

Main Methods:

• Analysis of serum phosphate levels using an unreduced phosphomolybdate method.
• Investigation of the reaction mixture for interfering substances.
• Clinical correlation with patient diagnosis of multiple myeloma.

Main Results:

• Falsely elevated serum phosphate levels were observed in two multiple myeloma patients.
• The elevated values were attributed to the formation of a proteinaceous suspension in the reaction mixture.
• The interference was specific to the unreduced phosphomolybdate method without dialysis.

Conclusions:

• The unreduced phosphomolybdate method can lead to spurious hyperphosphataemia in multiple myeloma.
• Protein interference in laboratory assays may be underestimated.
• Clinicians should consider potential assay interference when interpreting phosphate levels in myeloma patients.