The predictive power of serum κ/λ ratios for discrimination between monoclonal gammopathy of undetermined significance and multiple myeloma

Interlaboratory study of free monoclonal immunoglobulin light chain quantification

BACKGROUND

Quantification of monoclonal immunoglobulin free light chains (FLCs) in serum is used increasingly in clinical practice for the diagnosis, prognostic assessment, and treatment monitoring of monoclonal gammopathies. It is used as an adjunct to standard serum protein electrophoresis and immunofixation. However, methods for FLC quantification need further standardization and validation.

METHODS

The Czech Myeloma Group and the Czech Society of Clinical Biochemistry have initiated an interlaboratory study where six laboratories collaborating with the primary myeloma treatment centres measured FLC concentrations in 12 serum samples from patients with monoclonal gammopathies.

RESULTS

Repeatability of the measurements in five laboratories was calculated based on differences between the results of duplicate measurements. We found that repeatability depended more on the laboratory than on the device used for measurement.

CONCLUSIONS

The study revealed several weak points in the methodology, including the need for a uniform sample dilution procedure. Interlaboratory reproducibility was comparable with values achieved in the NEQAS programme. Because the κ/λ ratio cannot be measured with high precision, κ and λ FLC concentrations should be used where possible. Due to its impact on the clinical management of patients with gammopathy, FLC quantification needs to become a part of the regular quality control cycle in myeloma centres.

Retrospective study of monoclonal gammopathies detected in the clinical laboratory of a Spanish healthcare district: 14-year series

BACKGROUND

We studied the incidence, classification and isotype distribution of monoclonal gammopathies and M-protein detected between 1992 and 2005 inclusive in the clinical laboratory of a healthcare district in Madrid (Spain) with an average population of 280,574 inhabitants.

METHODS

Serum electrophoresis was carried out on a cellulose acetate support up until 1997, and then using capillary zone electrophoresis systems, with M-protein identification carried out by agarose gel immunofixation. The age-adjusted incidences were standardized with respect to the WHO World Standard Population Distribution, based on the world average population between 2000 and 2025. The clinical diagnosis was recorded from the patient case history.

RESULTS

M-protein was detected in a total of 537 patients; of these, 42 had been diagnosed before 1992, representing a 0.19% prevalence in our population. The mean age-adjusted incidence of monoclonal gammopathy was 10.72 per 100,000 inhabitants/year (SE 1.31), ranging from 4.85/100,000 in 1992 to 14.28/100,000 in 2003 and 2004. The median patient age at diagnosis was 73 years (range 25-96 years), with males accounting for 46.8% of all cases of monoclonal gammopathy, and 57.8% of all malignant monoclonal gammopathies. A total of 54.1% of the patients were clinically defined as presenting monoclonal gammopathy of undetermined significance, 31.3% presented multiple myeloma, and the remaining 14.6% presented malignant gammopathies. The most frequent M-protein isotype was IgG (55.8%), followed by IgA (20.8%) and IgM (13.6%). A total of 88% of the light chain M-proteins, 54% of isotype IgM, 51% of isotype IgA and 36% of isotype IgG were associated with B lymphoproliferative diseases.

CONCLUSIONS

We conclude that the clinical laboratory should play an important role in the study of monoclonal gammopathies, since it is the only location where all M-protein patients are observed. On the other hand, studies of this type should be carried out over long-term periods, owing to the variations we have noted in the detection of M-proteins.