Rapid detection of serum free light chains by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Introduction: Serum free light chain (FLC) measurements are increasingly prominent for patients with plasma cell disorders (PCDs) in screening, prognostic stratification, and monitoring therapy responses. Objectives: We aimed to develop a sensitive, reliable, and accurate method for diagnosing PCDs that can notably decrease the time and cost of current methods. Methods: Here, we present a novel approach for FLC measurement using immunoenrichment on micro-affinity chromatography in combination with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) detection. In this study, serum free kappa (kappa) and free lambda (lambda) light chain (LC) levels in the serum of 105 patients were compared between the nephelometric serum FLC quantification and MALDI-TOF MS detection. Results: Cohen's kappa coefficient between the MALDI-TOF MS-based method and the FLC assay revealed an almost perfect agreement in the case of normal (negative) results (kappa = 0.92; 95% confidence interval (CI): 0.837 to 0.968) and a good agreement in the case of increased (positive) results (kappa = 0.76; 95% CI: 0.608 to 0.870). In Spearman's correlation analysis, the best correlation was found between serum free kappa/lambda ratios (r = 0.628, 0.496 to 0.732; p <0.0001). Our method showed sensitivity (92.5%) and specificity (76.3%) for discrimination between the kappa/lambda FLC ratio compared to the serum FLC assay. Conclusion: The proposed method can significantly contribute to diagnosing and monitoring PCDs as it can significantly be time-saving, cost-effective in FLC measurement.

Automated summary

A novel method for measuring serum free light chains (FLCs) using immunoenrichment on micro-affinity chromatography in combination with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) detection was developed. The results showed good agreement between the proposed method and the FLC assay, making it a valuable tool for screening, prognostic stratification, and monitoring therapy responses in plasma cell disorders (PCDs).