Spurious hyperphosphataemia caused by an IgA paraprotein: a topic revisited.
BACKGROUND
There are reports in the literature describing artefactually raised phosphate concentrations in serum samples of patients with myeloma. However, IgA paraproteins have been reported only rarely as a potential cause.


METHODS
Following the detection of a grossly elevated phosphate concentration in a patient with an IgA paraprotein and another with an IgG paraprotein, we estimated phosphate concentrations in a further 73 patients with paraproteins using the Bayer ADVIA 1650 and Ortho Vitros 950 analysers. The latter method has been reported to be unaffected by pseudohyperphosphataemia.


RESULTS
Deproteinization of the serum samples containing the IgA and IgG paraproteins showed that they were responsible for the interference. No significant difference in serum phosphate concentrations measured by the two analysers was noted for the larger study of serum IgG or IgM paraproteins. However, a statistically significant but clinically trivial difference in phosphate concentration was noted for serum IgA paraproteins, with the Ortho Vitros 950 giving slightly higher phosphate concentrations. Deproteinization of these samples yielded similar phosphate concentrations. Phosphate estimation in serum samples without paraproteins using both analysers yielded results that were not statistically different.


CONCLUSIONS
On occasion, serum samples containing IgA paraproteins may give rise to erroneous phosphate concentrations when the Bayer ADVIA is used
Sinclair
David
D
Department of Clinical Biochemistry, Queen Alexandra Hospital, Portsmouth PO6 3LY, UK. david.sinclair@porthosp.nhs.uk
Smith
Helen
H
Woodhead
Pamela
P
D001671:Biochemistry / Q000295:instrumentation / Q000379:methods; D002138:Calibration; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007074:Immunoglobulin G / Q000097:blood*; D009101:Multiple Myeloma / Q000097:blood*; D010266:Paraproteins / Q000032:analysis*; D010710:Phosphates / Q000097:blood*; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D007070:Immunoglobulin A; D007074:Immunoglobulin G; D010266:Paraproteins; D010710:Phosphates