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Spurious hyperphosphataemia caused by an IgA paraprotein: a topic revisited
David Sinclair1, Helen Smith, Pamela Woodhead
1Department of Clinical Biochemistry, Queen Alexandra Hospital, Portsmouth PO6 3LY, UK. david.sinclair@porthosp.nhs.uk
Annals of Clinical Biochemistry
|March 18, 2004
Summary
Immunoglobulin A (IgA) paraproteins can cause falsely high serum phosphate levels, particularly with the Bayer ADVIA 1650 analyser. This interference, though often minor, requires careful consideration in myeloma patients.
Area of Science:
- Clinical Chemistry
- Hematology
- Analytical Biochemistry
Background:
- Artefactual elevations in serum phosphate are documented in myeloma patients.
- Immunoglobulin A (IgA) paraproteins are rarely implicated as a cause of pseudohyperphosphataemia.
Purpose of the Study:
- To investigate the potential for IgA paraproteins to cause falsely elevated serum phosphate concentrations.
- To compare phosphate measurements using two different analytical methods in patients with paraproteins.
Main Methods:
- Serum phosphate was measured in 73 patients with paraproteins using Bayer ADVIA 1650 and Ortho Vitros 950 analysers.
- Samples with IgA and IgG paraproteins were deproteinized to identify interference sources.
- Phosphate levels were compared between analysers for different paraprotein types and in samples without paraproteins.
Main Results:
- Deproteinization confirmed IgA and IgG paraproteins caused interference.
- No significant difference in phosphate levels was observed for IgG or IgM paraproteins between the two analysers.
- A statistically significant but clinically insignificant difference was noted for IgA paraproteins, with the Ortho Vitros 950 yielding slightly higher results.
Conclusions:
- Serum samples with IgA paraproteins can occasionally lead to erroneous phosphate concentrations when using the Bayer ADVIA 1650 analyser.
- The interference is specific to certain paraprotein types and analytical methods.