False increase in serum C-reactive protein caused by monoclonal IgM-lambda: a case report.

Area of Science:

• Clinical Chemistry
• Immunology
• Laboratory Medicine

Background:

• Human anti-animal antibodies are known interferents in laboratory diagnostics.
• High-titer autoantibodies can lead to inaccurate patient test results, affecting clinical decisions.

Observation:

• An 86-year-old man presented with markedly elevated C-reactive protein (CRP) levels (>500 mg/l).
• Discrepancies in CRP measurements across different assays prompted further investigation.
• Protein electrophoresis revealed a monoclonal IgM-lambda paraprotein that interfered with the initial CRP assay.

Findings:

• The patient's IgM-lambda paraprotein (7 g/l) specifically bound to goat anti-CRP antibodies used in an automated immunometric assay.
• Removal of the paraprotein corrected the falsely elevated CRP values, which then measured <12 mg/l.
• The paraprotein was attributed to monoclonal gammopathy of unknown significance, with no evidence of hematologic malignancy.

Implications:

• This case highlights the critical need to consider antibody-mediated interference in immunoassays.
• Accurate diagnostic interpretation requires awareness of paraproteins and their potential to cause false positives in C-reactive protein testing.
• Developing strategies to mitigate heterophile antibody interference is crucial for reliable laboratory diagnostics.