The lipemia index: an efficient screening tool for identifying IgM paraprotein-mediated interference in the Beckman Coulter AU5800 uric acid assays.

Objectives: IgM paraprotein-mediated interference in Uric Acid (UA) measurement remains a significant challenge in clinical labs, potentially compromising hyperuricemia diagnosis and management. This study investigated the identification and elimination strategies for IgM interference in the Beckman Coulter AU5800 UA assays.

Methods: Serum samples without hemolysis, icterus, or lipemia from 196 patients with IgM paraproteinemia were analyzed for UA levels based on uricase-peroxidase enzymatic reaction and lipemia (LIP) index levels via transmission turbidimetry. Polyethylene glycol (PEG) precipitation and 5-fold dilution of distilled water or isotonic saline were applied for eliminating IgM interference.

Results: Artificially decreased UA results caused by IgM interference were detected in 24.5 % of patients with IgM paraproteinemia. Waldenström's macroglobulinemia diagnosis, IgM-κ subtype, increased serum levels of IgM and LIP index were independent risk factors for IgM interference. The area under the curve of serum LIP index for identifying IgM interference in UA assays were 0.937, with 89.6 % sensitivity and 93.2 % specificity. The degree of IgM interference demonstrated positive correlation with LIP index levels (r = 0.581, p < 0.001). 15 % PEG precipitation restored reaction curves of all samples with interference to normal morphology and increased UA results with a median recovery of 61.0 % (30.5-83.0 %). Similar effect was achieved through 5-fold dilution with distilled water followed by centrifugation, whereas isotonic saline dilution was usually ineffective.

Conclusions: These findings suggested elevated serum LIP index without visible lipemia as an efficient screening tool for identifying IgM paraprotein-mediated interference in UA assays, and 15% PEG precipitation as an optimal intervention for mitigating IgM interference.