Detection of serum free light chains: the problem with antigen excess.

BACKGROUND: In recent years, measurement of serum immunoglobulin free light chains (FLCs) has greatly facilitated diagnosis and monitoring of various plasma cells dyscrasias, including multiple myeloma. Detection of FLCs by nephelometry depends on the formation of immune complexes. However, it is known that if the antigen (free light chain) is present in great excess, non-precipitating immune complexes can be formed and be detected poorly. This may lead to inaccurate test results. METHODS: Serum samples from 91 patients were subjected prospectively to the detection of free κ and λ light chains by automated nephelometry. A standard dilution of 1:100 was paralleled by a 1:2000 dilution. In addition, samples with values below the effective range (1:100) were subjected to a 1:20 dilution in order to calculate the κ/λ ratio. RESULTS: Here, we report the incidence of antigen excess in a cohort of 91 patients with a high proportion of monoclonal abnormalities. A standard dilution (1:100) of free light κ chains from a patient with monoclonal immunoglobulin A κ gammopathy were missed repeatedly. In a second patient (with myeloproliferative disease and an apparent incidental FLC monoclonal gammopathy of undetermined significance) free λ chains were also substantially underestimated in the standard dilution. Hence, the incidence of erroneously low test results due to antigen excess was 2.20%. CONCLUSIONS: We found a significantly higher incidence of falsely low test results due to antigen excess than reported previously. Antigen excess may result in erroneous interpretations in sera subjected to nephelometric analysis. Therefore, clinical decisions should not be based solely on a single assay, especially if FLC testing includes only one dilution of the serum sample. Instead, several parallel dilutions should be recommended for screening of patients.

Workflow and cost analysis on MODULAR ANALYTICS.

Four stand-alone analyzers in a centralized laboratory were replaced by two modular analytical systems processing 45 methods of the general chemistry and specific protein segment. This consolidation led to a reduction of the daily workflow and operational costs. The cost saving with 1.3 million reported results per year was 53,000 Euro, which can be assessed as an important contribution to cost reduction in the health care system.

MODULAR ANALYTICS: A New Approach to Automation in the Clinical Laboratory.

MODULAR ANALYTICS (Roche Diagnostics) (MODULAR ANALYTICS, Elecsys and Cobas Integra are trademarks of a member of the Roche Group) represents a new approach to automation for the clinical chemistry laboratory. It consists of a control unit, a core unit with a bidirectional multitrack rack transportation system, and three distinct kinds of analytical modules: an ISE module, a P800 module (44 photometric tests, throughput of up to 800 tests/h), and a D2400 module (16 photometric tests, throughput up to 2400 tests/h). MODULAR ANALYTICS allows customised configurations for various laboratory workloads. The performance and practicability of MODULAR ANALYTICS were evaluated in an international multicentre study at 16 sites. Studies included precision, accuracy, analytical range, carry-over, and workflow assessment. More than 700 000 results were obtained during the course of the study. Median between-day CVs were typically less than 3% for clinical chemistries and less than 6% for homogeneous immunoassays. Median recoveries for nearly all standardised reference materials were within 5% of assigned values. Method comparisons versus current existing routine instrumentation were clinically acceptable in all cases. During the workflow studies, the work from three to four single workstations was transferred to MODULAR ANALYTICS, which offered over 100 possible methods, with reduction in sample splitting, handling errors, and turnaround time. Typical sample processing time on MODULAR ANALYTICS was less than 30 minutes, an improvement from the current laboratory systems. By combining multiple analytic units in flexible ways, MODULAR ANALYTICS met diverse laboratory needs and offered improvement in workflow over current laboratory situations. It increased overall efficiency while maintaining (or improving) quality.