Paraprotein interference in bilirubin assays: A case of multiple myeloma highlighting the reliability of dry chemistry.
Aditya Narayanan S, Ramya Devi D A, Renuka Pangaluri et al.
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Case in brief
A 60-year-old man with nonspecific symptoms had no jaundice and normal-appearing imaging. Wet chemistry testing reported total bilirubin of 0.39 mg/dL and an impossible direct bilirubin of -7.67 mg/dL. Repeat testing by dry chemistry showed total bilirubin of 1.0 mg/dL and direct bilirubin of 0.1 mg/dL, consistent with the clinical findings. Further investigation confirmed multiple myeloma with IgG-kappa monoclonal gammopathy; the discordant wet chemistry result was attributed to paraprotein interference.
What made this case unusual
The paraprotein-associated assay interference produced a negative direct bilirubin result on wet chemistry, an analytically impossible value that conflicted with the clinical picture.
Diagnostic / clinical pearl
An impossible bilirubin result that conflicts with clinical findings should prompt consideration of analytical interference; in this case, dry chemistry testing provided results consistent with the patient’s presentation.
Why it matters
Recognizing paraprotein interference can help prevent misleading biochemical interpretation and unnecessary workup.