Heavy/light chain specific immunoglobulin ratios provides no additional information than serum proteins electrophoresis and immunofixation for the diagnosis and the follow-up of intact immunoglobulin multiple myeloma patients

Understanding the Constraints and Optimization of Serum Immunofixation Electrophoresis and Serum Free Light Chains for Detecting Monoclonal Proteins: A Single-Center Experience

Introduction  Serum immunofixation electrophoresis (SIFE) and serum free light chain (SFLC) assay are imperative investigations in diagnosis and follow-up of multiple myeloma (MM). SFLC assays are reported to have higher sensitivity than SIFE. However, discrepancies have been reported between them. The current study was aimed at assessing concordance and discordance between SIFE and SFLC results in MM. Methods  A total of 450 observations of both SIFE and SFLC were obtained from treatment-naive and follow-up MM patients. Results  One hundred and twenty-nine (28.7%) values were observed as discordant, that is, positive SIFE with normal SFLC ratio or negative SIFE with abnormal SFLC ratio ( p -value < 0.00001). Proportion of discordance was higher in SIFE positive-SFLC normal cases than SIFE negative-SFLC abnormal cases. Discordance was more frequent in follow-up cases. Conclusion  Negative SFLC alone may not be reliable for MM follow-up. Algorithm may be based on SFLC measurements on each follow-up till attainment of normal SFLC ratio. Once SFLC normalizes, follow-up may be done with SIFE. If SIFE is positive, further follow-up with SIFE may be initiated.

Accurate Quantification of Monoclonal Immunoglobulins Migrating in the Beta Region on Protein Electrophoresis

BACKGROUND

The concentration of monoclonal immunoglobulins (Igs) in neoplastic monoclonal gammopathic manifestations is generally measured by densitometric scanning of the monoclonal peaks on gel or by measuring absorbance at 210 nm in capillary electrophoresis (CE). For monoclonal Igs migrating in the beta region, measurement is complicated by the major beta-region proteins, namely, transferrin and C3.

METHODS

C3 interference in densitometry was eliminated by heat treatment of serum, and monoclonal Igs were quantified by densitometry of the residual band. The immunochemical measurement of transferrin was converted to its equivalent densitometric quantity. For monoclonal Ig migrating with transferrin, the contribution of the latter was removed by subtracting the converted transferrin concentration from the combined densitometric quantification of the band. With CE, monoclonal Ig was measured by using immunosubtraction (ISUB) to guide demarcation.

RESULTS

The results obtained using the C3 depletion and transferrin subtraction method were lower and yet comparable to the results derived from using CE measurement guided by ISUB. As we expected, the results from both methods were lower than those derived from a perpendicular drop measurement of the peak or via nephelometric assay of the involved isotype.

DISCUSSION

Accurate measurement of monoclonal Igs is important for the diagnosis and monitoring of monoclonal gammopathic manifestations. Determination of serum free light chain concentration per gram of monoclonal Ig is an essential measure for the diagnosis of light chain-predominant multiple myeloma. The method described herein improves accuracy of measurements for monoclonal Igs migrating in the beta region, without the need for special reagents or equipment.

Serum and Urine Protein Electrophoresis and Serum-Free Light Chain Assays in the Diagnosis and Monitoring of Monoclonal Gammopathies

BACKGROUND

Laboratory methods for diagnosis and monitoring of monoclonal gammopathies have evolved to include serum and urine protein electrophoresis, immunofixation electrophoresis, capillary zone electrophoresis, and immunosubtraction, serum-free light chain assay, mass spectrometry, and newly described QUIET.

CONTENT

This review presents a critical appraisal of the test methods and reporting practices for the findings generated by the tests for monoclonal gammopathies. Recommendations for desirable practices to optimize test selection and provide value-added reports are presented. The shortcomings of the serum-free light chain assay are highlighted, and new assays for measuring monoclonal serum free light chains are addressed.

SUMMARY

The various assays for screening, diagnosis, and monitoring of monoclonal gammopathies should be used in an algorithmic approach to avoid unnecessary testing. Reporting of the test results should be tailored to the clinical context of each individual patient to add value. Caution is urged in the interpretation of results of serum-free light chain assay, kappa/lambda ratio, and myeloma defining conditions. The distortions in serum-free light chain assay and development of oligoclonal bands in patients' status post hematopoietic stem cell transplants is emphasized and the need to note the location of original monoclonal Ig is stressed. The need for developing criteria that consider the differences in the biology of kappa and lambda light chain associated lesions is stressed. A new method of measuring monoclonal serum-free light chains is introduced. Reference is also made to a newly defined entity of light chain predominant intact immunoglobulin monoclonal gammopathy. The utility of urine testing in the diagnosis and monitoring of light chain only lesions is emphasized.

Risk Stratification in Multiple Myeloma

There are many prognostic variables in multiple myeloma and the difficulty is in deciding which is truly significant. The widely used International Staging System (ISS) does not incorporate genetics, age, and other important variables in its risk stratification. Although it has its own limitations, the recently published Revised International Staging System (R-ISS) that was built upon the framework of ISS, is a more comprehensive and predictive tool for multiple myeloma patients and should be henceforth utilised. We will review the current prognostic variables and their significance in this paper.

Serum Free Light Chain Assay and κ/λ Ratio: Performance in Patients With Monoclonal Gammopathy-High False Negative Rate for κ/λ Ratio

Background

Serum free light chain assay (SFLCA) and κ/λ ratio, and protein electrophoretic methods are used in the diagnosis and monitoring of monoclonal gammopathies.

Methods

Results for serum free light chains, serum and urine protein electrophoreses and immunofixation electrophoreses in 468 patients with a diagnosis of monoclonal gammopathy were compared. The results of the two methods were graded as concordant, non-concordant or discordant with the established diagnoses to assess the relative performance of the methods. Results of κ/λ ratio in samples with monoclonal protein detectable by electrophoretic methods were also analyzed.

Results

Protein electrophoreses results were concordant with the established diagnoses significantly more often than κ/λ ratio. The false negative rate for κ/λ ratio was higher than that for electrophoretic methods. κ/λ ratio was falsely negative in about 27% of the 1,860 samples with detectable monoclonal immunoglobulin. The false negative rate was higher in lesions with lambda chains (32%) than those with kappa chains (24%). The false negative rate for κ/λ ratio was over 55% in samples with monoclonal gammopathy of undetermined significance. Even at first encounter, the false negative rates for κ/λ ratios for monoclonal gammopathy of undetermined significance, smoldering myeloma and multiple myeloma were 66.98%, 23.08%, and 30.15%, respectively, with false negative rate for lambda chain lesions being higher.

Conclusions

Electrophoretic studies of serum and urine are superior to SFLCA and κ/λ ratio. Abnormal κ/λ ratio, per se, is not diagnostic of monoclonal gammopathy. A normal κ/λ ratio does not exclude monoclonal gammopathy. False negative rates for lesions with lambda chain are higher than those for lesions with kappa chains. Electrophoretic studies of urine are underutilized. Clinical usefulness and medical necessity of SFLCA and κ/λ ratio is of questionable value in routine clinical testing.