FLC Assays Research Articles

Performance Characteristics and Limitations of the Available Assays for the Detection and Quantitation of Monoclonal Free Light Chains and New Emerging Methodologies.

Light chain measurements form an essential component of the testing strategy for the detection and monitoring of patients with suspected and/or proven plasma cell disorders. Urine-based electrophoretic assays remain at the centre of the international guidelines for response assessment but the supplementary role of serum-free light chain (FLC) assays in response assessment and the detection of disease progression due to their increased sensitivity has been increasingly recognised since their introduction in 2001. Serum FLC assays have also been shown to be prognostic across the spectrum of plasma cell disorders and are now incorporated into risk stratification scores for patients with monoclonal gammopathy of undetermined significance (MGUS), smouldering multiple myeloma, and light chain amyloidosis (AL amyloidosis), as well as being incorporated into the criteria for defining symptomatic multiple myeloma. There are now multiple different commercially available serum FLC assays available with differing performance characteristics, which are discussed in this review, along with the implications of these for patient monitoring. Finally, newer methodologies for the identification and characterisation of monoclonal FLC, including modifications to electrophoretic techniques, mass spectrometry-based assays and Amylite, are also described along with the relevant published data available regarding the performance of each assay.

Accuracy of determination of free light chains (Kappa and Lambda) in plasma and serum by Swedish laboratories as monitored by external quality assessment

BackgroundFree light chain (FLC) measurements are important in diagnosing monoclonal gammopathies. As FLC are heterogeneous, different reagents and instruments for measuring FLC concentrations may give diverging results that affect assessment of patients with monoclonal gammopathies. Here we investigated agreement between different FLC methods using data from the Swedish external quality assurance (EQA) programme. MethodsThe two main FLC assays, N Latex FLC (Siemens) and Serum Freelite (The Binding Site), using four nephelometric or turbidimetric instrument platforms, were compared. Results from 27 EQA rounds distributed to 11–16 Swedish hospital laboratories during 2015–2020 were investigated. ResultsThe kappa (κ) FLC measurements deviated significantly over time, but when only nephelometry was used, deviation from the mean was lower (median ranges: −5% to 13 %). The CV was significantly higher for the Freelite assay (mean CV = 8.7) than for the N latex assay (mean CV = 5.7) (p < 0.0001). The coefficient of determination between all combinations of reagents and instrument platforms used was generally good (r2 = 0.76–0.87), and the correlation slope acceptable (0.81–1.2). For lambda (λ) FLC measurements, no concordance between combinations of instruments and reagents is apparent, deviating between −40 % to + 48 % from the mean. The CV was significantly higher for the combination with nephelometry and the Freelite assay (CV mean = 13.9 %) than nephelometry and the N latex assay (CV mean = 9.9 %) (p <0.001). The coefficient of determination varied between combinations of reagents and instrument platforms (r2 = 0.59–0.89) and the slope ranged between 0.48 and 1.5. Significant differences between the two reagents used were sometimes noted. ConclusionsImprecision in λFLC affects the κFLC/λFLC ratio. This may be important in clinical assessment of patients, especially differentiating between monoclonal and polyclonal gammopathies.

Serum free light chain analysis: persisting limitations with new kids on the block.

Serum free light chain (sFLC) measurements have inherent analytical limitations impacting sFLC clinical interpretation. We evaluated analytical and diagnostic performance of three polyclonal sFLC assays on four analytical platforms. sFLC concentration was measured using Diazyme FLC assays (Diazyme) on cobas c501/c503 analyzer (Roche); Freelite assays (The Binding Site) on Optilite analyzer (The Binding Site) and cobas c501 analyzer and Sebia FLC ELISA assays (Sebia) on AP22 ELITE analyzer (DAS). Imprecision, linearity, method comparison vs. Freelite/Optilite, antigen excess detection and reference value verification were assessed. Diagnostic performance was compared on 120 serum samples and on follow-up samples of five patients with κ and λ monoclonal gammopathy. Method comparison showed excellent correlation with Freelite/Optilite method for all assays. A large proportional negative bias was shown for both Sebia κ and λ ELISA and a significant positive proportional bias for λ in the low (<10mg/L) Freelite/cobas c501 method. Clinically relevant underestimation of κ sFLC levels due to antigen excess was shown for 7% of each Diazyme/cobas application and for 11 and 32.1% of λ sFLC assay of respectively Diazyme/cobas and Sebia/AP22. sFLC reference values revealed application specific. Cohen's κ values were (very) good for κ sFLC but only moderate to good for λ sFLC. In 4/10 follow-up patients, significant differences in clinical interpretation between sFLC assays were noticed. Important analytical limitations remain for all sFLC applications. Differences in reference values and diagnostic performance hamper interchangeability of sFLC assays. Assay specific sFLC decision guidelines are warranted.

Evaluation of the siemens N Latex free light chain assay and comparison to Binding Site Freelite™ assay

Abstract Introduction/Objective The International Myeloma Working Group (IMWG) guidelines include serum free light chain (sFLC) level and κ/λ ratio as excellent indicators of clonality. The Binding Site Freelite ™ was the first FDA approved assay for quantitative measurement of sFLC, the assay was based on a mixture of polyclonal antibodies directed against a variety of FLC epitopes. The Siemens N-Latex assay employs a probe mixture of mouse monoclonal antibodies. Both assays can be run on nephelometers. We assessed the analytical performance of the N-Latex assays and compared it with the Freelite™ assays. Methods/Case Report Analytical accuracy, precision, reproducibility and linearity were evaluated according to the regulatory standards. Method comparison was performed with 220 clinical samples for statistic correlation and clinical concordance analysis. Results (if a Case Study enter NA) The N-Latex FLC κ and λ assays had coefficient variation of 1-5% with-in run and 3-8% between run precision. Accuracy was verified using assayed controls in the duration of 21 days. Within analytical measuring range, almost perfect linearity was achieved for both κ and λ FLC assays. In comparison study to Freelite™ with 220 clinical samples, good agreement in classification was observed for κ, λ and κ/λ ratio (Cohen’s κ 0.73, 0.82 and 0.87). Pearson correlation analysis showed correlation coefficient value r &amp;gt;0.90 for all the analytes. Conclusion The N-Latex FLC assay has good analytical performance, did not exhibit gross antigen excess and can be used in clinical practice. However, it showed markedly lower absolute values for κ/λ ratio compared with Freelite™. Our data demonstrated that although good clinical concordance between N-Latex and Freelite™ FLC assays was achieved, the absolute values from the two assay are not interchangeable. Further studies in modification of the assay-specific diagnostic (involved FLC/non-involved FLC) thresholds for smoldering multiple myeloma (SMM) and multiple myeloma (MM) are needed.

Serum Free Light Chain Assay Measurement at Disease Relapse for Prognostication in Patients with Multiple Myeloma in the Novel Agent Era

BackgroundMonoclonal serum free light chains (sFLC) are detected in patients with B-cell proliferative disorders including multiple myeloma (MM) at diagnosis and disease relapse. Several previous studies demonstrated prognostic impact of the involved and uninvolved sFLC ratio (rFLC) in patients with newly diagnosed MM, patients with monoclonal gammopathy with undetermined significance, and smoldering MM. However, the prognostic impact of rFLC and differences between involved and uninvolved FLCs (dFLC) at the time of disease relapse have not been fully elucidated.Patients and methodsWe identified consecutive patients with symptomatic MM, diagnosed and treated at Kameda Medical Center from January 2006 to April 2017. Patients who experienced initial relapse during June 2007 (the time where we began to routinely measure sFLC in MM patients) to April 2017 were identified. We reviewed background and outcome data from the electronic record. IMWG response criteria were used for assessing response and disease progression. rFLC was defined as involved FLC (iFLC) level divided by uninvolved FLC (uFLC) level. dFLC was calculated by subtracting uFLC from iFLC. Time to second progression (2nd TTP) and overall survival after first relapse (OS after 1st relapse) were defined as the time from the date of first progression to the date of second progression and death from any cause, respectively. Receiver operating characteristic (ROC) analysis determined optimal cutoff levels of rFLC and dFLC. We divided patients into high or low rFLC or dFLC, according to these cutoff levels. To clarify the relationship between rFLC increase at relapse and subsequent prognosis, patients were divided into 4 groups according to the rFLC levels: patients with rFLC >0 and ≤10, >10 and ≤100, >100 and ≤1000, and >1000.ResultsThere were 240 patients diagnosed with symptomatic MM. Among them, 124 patients experienced disease relapse at least once during the observation period. Of the 124 patients, 97 were classified as having intact immunoglobulin MM and 27 had light chain MM. Median observation period from first relapse and age at first relapse of the 124 patients was 19.8 (range: 0.7 - 111.4) months (m) and 73.7 (range: 46.7 - 90.1) years, respectively. All patients received novel induction therapy agents. Using ROC analysis, we determined the optimal cutoff of rFLC and dFLC for predicting highest risk of second relapse within 1 year of first relapse as 19.7 and 122.9 mg/L, respectively. Patients with higher rFLC (n=57) had significantly shorter 2nd TTP and OS after 1st relapse than those with lower rFLC (n=67) (median 2nd TTP, 4.1 vs 24.7 m; P<0.001, and median OS after 1st relapse, 19.3 vs 42.7 m; P<0.001, respectively). Patients with higher dFLC (n=57) had significantly shorter 2nd TTP and OS after 1st relapse than those with lower rFLC (n=67) (median 2nd TTP, 5.5 vs 20.5 m; P<0.001, median OS after 1st relapse, 19.1 vs 42.7 m; P<0.001, respectively). Both 2nd TTP and OS after 1st relapse were significantly shorter when associated with increased rFLC levels. The median survival of patients with rFLC >0 and ≤10 (n=57), >10 and ≤100 (n=30), >100 and ≤1000 (n=22), and >1000 (n=15) were 30.5, 9.9, 4.7 and 1.6 m, respectively for 2nd TTP and 72.6, 33.6, 24.9 and 14.7 m respectively for OS after 1st relapse (both, P<0.001), whereas no significant difference was detected among the four risk groups of patients for age at first relapse, international staging system (ISS), revised ISS, the level of albumin, beta-2 microglobulin, creatinin, hemoglobin, lactate dehydrogenase abnormality, high-risk cytogenetic abnormality, or chemotherapy after first relapse.ConclusionAt disease relapse, both rFLC and dFLC clearly identified different patient risk groups for subsequent prognosis. High rFLC and dFLC at relapse related to shorter 2nd TTP and OS after 1st relapse. Our data indicate that serial measurement of serum FLC assays may predict prognosis after relapse in patients with MM who receive novel agents and experience disease progression. [Display omitted] DisclosuresKitadate:Kyowa Kirin: Research Funding; Eisai: Research Funding; Asahi Kasei: Research Funding; Pfizer: Research Funding; Otsuka: Research Funding; Chugai: Research Funding; Novartis: Research Funding; Fujimoto: Research Funding; Toyama kagaku: Research Funding.

Comparison of 2 Serum-Free Light-Chain Assays in CKD Patients

IntroductionQuantification of serum-free light chains (FLCs) is important in the diagnosis and monitoring of paraprotein-related diseases. There are currently 2 FLC assays available: the Freelite assay (Binding Site) and the N Latex assay (Siemens). There is emerging evidence that these assays give different results, but it is not established how kidney dysfunction affects these assays differently.MethodsIn this study, we measured and compared serum FLCs in patients with mild-to-moderate chronic kidney disease (CKD) using both assays.ResultsAlthough κ FLCs are higher by Freelite, λ FLCs are higher by N Latex. Both κ and λ FLCs correlate inversely with estimated glomerular filtration rate (eGFR) in the 2 assays, but this effect is more pronounced in λ-free light-chain measurement by N Latex. Consequently, although the κ/λ ratio by Freelite is inversely correlated by eGFR, the κ/λ ratio by N Latex is positively correlated with eGFR.ConclusionOur results clearly demonstrate that the 2 available FLC assays cannot be used interchangeably in patients with CKD.

Direct Detection of Monoclonal Free Light Chains in Serum by Use of Immunoenrichment-Coupled MALDI-TOF Mass Spectrometry

Free light chain (FLC) quantification is the most analytically sensitive blood-based method commercially available to diagnose and monitor patients with plasma cell disorders (PCDs). However, instead of directly detecting monoclonal FLCs (mFLCs), FLC assays indirectly assess clonality based on quantifying κ and λ FLCs and determination of the к/λ FLC ratio. Often an abnormal FLC ratio is the only indication of a PCD, and confirmation by a direct method increases diagnostic confidence. The aim of this study was to develop an analytically sensitive method for direct detection of mFLCs. Patient sera (n = 167) previously assessed by nephelometric FLC quantification and immunofixation electrophoresis (IFE) were affinity enriched for IgG, IgA, and total and free κ and λ light chains and subjected to MALDI-TOF MS. Relative analytical sensitivity of these methods was determined using serially diluted sera containing mFLCs. In sera with abnormal FLC ratios (n = 127), 43% of monoclonal proteins were confirmed by IFE, 57% by MALDI-TOF MS without FLC enrichment, and 87% with FLC enrichment MALDI-TOF MS. In sera with normal FLC ratios (n = 40), the FLC MALDI-TOF MS method identified 1 patient with an mFLC. Serial dilution and analysis of mFLC containing sera by IFE, nephelometry, and FLC MALDI-TOF MS demonstrated that FLC MALDI-TOF MS analysis had the highest analytical sensitivity. FLC immunoenrichment coupled to MALDI-TOF MS enables direct detection of mFLCs and significantly increases the confirmation of abnormal serum FLC ratios over IFE and MALDI-TOF MS without FLC enrichment, thereby providing added confidence for diagnosing FLC PCDs.

Method comparison for serum free light chain quantification between the Sebia FLC and Freelite assays

Method comparison for serum free light chain quantification between the Sebia FLC and Freelite assays

Prognostic value of involved/uninvolved free light chain ratio determined by Freelite and N Latex FLC assays for identification of high-risk smoldering myeloma patients.

Background Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell disorder with a high risk of progression to symptomatic multiple myeloma (MM). The serum free light chain (sFLC) ratio is a powerful prognostic factor for SMM: an sFLC ratio ≥8 has been reported to be associated with a high risk of progression to MM, and an sFLC ratio ≥100 has been described as a criterion for ultra-high-risk SMM, and has been integrated into the definition criteria for MM since 2014. However, all recommendations were based on sFLC measured using the first commercialized assay, Freelite™, while other assays are now available. We aimed to evaluate the safety and accuracy of N-Latex sFLC to identify high-risk and ultra-high-risk SMM. Methods The sFLC ratio was measured at diagnosis with both Freelite and N-Latex assays in a cohort of 176 SMM patients on a BN Prospec nephelometer. Demographic, clinical, therapeutic and laboratory data were collected at the time of diagnosis and at follow-up. Results Sixty-two patients (35.2%) progressed to MM within 2 years. Compared to Freelite™ sFLC, N Latex sFLC ratios ≥8 and ≥100 provided similar performances for the identification of high-risk and ultra-high risk SMM patients. Conclusions Our results evidenced that the N-Latex assay could be used for SMM monitoring, like Freelite. However, an N-Latex sFLC ratio ≥70 appears to provide similar performances to a Freelite sFLC ratio ≥100, with a slightly better positive predictive value. Both assays provided accurate identification of high-risk and ultra-high risk SMM patients. These results should be confirmed in an independent study.

Evaluation of the N-latex serum free light chain assay on the Siemens BNII analyzer and agreement with The Binding Site FreeLite assay on the SPAPlus

ObjectivesTo evaluate the Siemens N-latex kappa free light chain (κFLC) and lambda FLC (λFLC) assays on the BNII nephelometer and assess agreement with The Binding Site Freelite FLC assays on the SPAPlus. Design and methodsOver 180 patient serum samples from routine analysis of κFLC and λFLC measured by the Freelite assay were collected for the study and measured with the N-latex κFLC and λFLC assays to assess precision, linearity, method comparison and dilutional effects. ResultsComplex precision showed coefficients of variation of 4.8–7.2% for the κFLC assay and 3.6–6.0% for the λFLC assay. Linearity assessment showed both assays were linear (κFLC, y=1.00x−0.09 and λFLC, y=1.050x−1.252). Qualitative method comparison showed 87.9% (116/132) agreement and Cohen's kappa of 80.4% between the κFLC assays and 72.6% (98/135) agreement and Cohen's kappa of 55.4% for the λFLC assays. Quantitative method comparison for κFLC<150mg/L was y=0.92x+2.21, R=0.661 and for λFLC<150mg/L was y=7.90x−137.96, R=0.526. Dilutional effects including antigen excess and non-linearity were also examined. ConclusionsThe N-latex assay showed good precision and linearity with reasonable agreement to the Freelite assay. However, the assays should not be used interchangeably to monitor patients.

Comparison of the Freelite serum free light chain (SFLC) assay with serum and urine electrophoresis/immunofixation and the N Latex FLC assay

Few reports have compared available serum free light chain (SFLC) assays. Here, a retrospective audit of the Freelite SFLC assay compared results to electrophoresis (EP)/immunofixation (IFX) and the N Latex FLC assay.A total of 244 samples collected over 3.5 months were studied using the Freelite and N Latex FLC nephelometry assays. Results were compared with serum and/or urine EP/IFX. The precision and linearity of the N Latex FLC assay was examined.Detectable paraprotein by serum or urine EP/IFX was present in 94% of samples with kappa and 100% with lambda FLC restriction. The correlation between the assays was higher for kappa (rho = 0.97) than lambda (rho = 0.89) especially when lambda results were above the upper limit of normal (rho = 0.62). Agreement in the categorical diagnosis as measured by the Cohen's kappa statistic was good (0.70). The N Latex FLC assay displayed good precision and linearity. In discordant samples the Freelite and N Latex FLC assays had equivalent agreement with IFX.Traditional methods of EP/IFX detected paraproteins in the majority of cases. Correlation between the Freelite and N Latex FLC assay is better for kappa than lambda FLC. The two assays are not entirely equivalent. Care should be taken by interpreting physicians and laboratories considering switching assays.

Assessment of time from onset of first symptoms to the final diagnosis of multiple myeloma (MM) - possible risks and future solutions

Assessment of time from onset of first symptoms to the final diagnosis of multiple myeloma (MM) - possible risks and future solutions

Retrospective audit of the freeliteTM serum free light chain (SFLC) assay: testing patterns, concordance with serum and urine electrophoresis/immunofixation and correlation with the N latex FLC assay

Aims A retrospective audit of the Freelite™ SFLC assay was conducted to compare concordance with electrophoresis (EPG)/immunofixation (IFX) and correlation with the N latex FLC assay. Methods 244 samples collected over 3.5 months were studied by nephelometry using the Freelite™ and N Latex FLC assays. Results were compared with serum (S) and/or urine (UEPG)/IFX. The precision and linearity of the N latex FLC assay were examined. Results 94% of samples with kappa restriction, and 100% with lambda restriction had detectable paraprotein by SEPG/IFX or UEPG/IFX. The correlation between the two assays was good for kappa (R 2 = 0.935) but not lambda (R 2 = 0.775) especially when lambda was above the ULN (R 2 = 0.406). Agreement in the categorical diagnosis of restricted SFLC was good (Cohen's kappa = 0.701). In discordant samples the Freelite™ assay displayed higher agreement with IFX (53% vs 47%). The N latex FLC assay displayed good precision and linearity. Discussion SFLC testing is popular despite traditional methods detecting paraproteins in most cases. Correlation between the Freelite™ and N latex FLC assays is better for kappa than lambda FLC. The two assays are not equivalent and the Freelite™ assay displays better agreement with IFX. Care should be taken by interpreting physicians and laboratories considering switching assays.

Relationship between monoclonal gammopathy and cardiac amyloid type

Proper identification of cardiac amyloid type is essential for patient management, and has historically relied upon immunohistochemical- or immunofluorescence-based methods, often correlated with serum and urine protein electrophoresis (SPEP and UPEP) with immunofixation electrophoresis (IFE), and/or free light chain immunoassay (FLC). The recent implementation of mass spectrometry-based proteomic analysis for clinical amyloid typing allows us to determine the validity of these tests to predict amyloid type. Validity of SPEP/UPEP/IFE and FLC assays in cardiac amyloid prediction was examined. Retrospective analysis of two tertiary care populations (n=143, 2001-2010), of cardiac biopsy-proven amyloidosis, was performed. Amyloid of transthyretin (ATTR) type was found in 81 (57%) of 143 patients and immunoglobulin light chain amyloid was found in the remaining 62 (43%). SPEP/UPEP/IFE detected a monoclonal gammopathy in 76 individuals, 56 with AL and 20 with ATTR amyloid and was overall a poor predictor of AL amyloid in this patient population: specificity (75%; 95% CI, 65-83%) and positive predictive value (PPV 74%; 95% CI, 63-82%). The FLC assay detected an abnormal kappa/lambda ratio in 61 patients, 53 with AL and 8 with ATTR amyloid and was a better predictor of AL amyloid type in this patient population: specificity (90%, 95% CI, 82-95%) and PPV (87%, 95% CI, 76-93%). ATTR was the predominant amyloid type in this large cohort of endomyocardial biopsies characterized by mass spectrometry. Although FLC performs better than SPEP/UPEP/IFE, the performance of blood and urine studies for monoclonal proteins are not adequate to classify amyloid type. This large-scale retrospective analysis of cardiac amyloidosis shows that blood and urine monoclonal protein studies are not, by themselves, robust predictors of cardiac amyloid type in patients undergoing endomyocardial biopsy.

Presence of Dysregulated Immune Recovery (IMD) Following Autotransplant May Change the Type of Predominant Serum Light Chain and Elevate the Level in Patients with Multiple Myeloma (MM).

Abstract 4870It is well recognized that there is a period of transient mono- or oligo-clonal predominance of certain classes of immunoglobulins (Ig) following blood stem cell transplant due to limited repertoire of regenerating B lymphocytes. The phenomenon sometimes becomes a source of confusion for assessing response in MM patients after transplant. In the study, we sought to determine whether the IMD changes the type of predominant serum light chain or elevates the level, thereby making interpretations of the serum free light chain assay difficult. The study includes 53 MM patients (median age 60, range 37 – 77 years) who were uniformly treated, between September 2006 and May 2009, with induction chemotherapy, autotransplant following high-dose melphalan-based ablative therapy and post-transplant maintenance. Both conventional serum protein electrophoresis (SPEP) and the polyclonal antisera-based free light chain assay of the Binding Site (FLC assay) were serially obtained before and after transplant up to one year, at least once every 2 weeks. IMD is defined by an appearance of new mono- or oligo-clonal Ig in serum that later disappeared spontaneously. 24 patients had Ig G, 12 Ig A, 13 light chain only and 4 nonsecretory MM. 18 of 53 patients (34%) showed IMD in a median onset of 44 days (range 22 to 182) from the 1st autotransplant, and 7 of 23 (30%) in 64 days (range 52 to 230) following the 2nd autotransplant. The median duration of IMD was 51 (range 12 to 194) and 48 (range 15 to 318) days, following the 1st and 2nd transplant, respectively. Of the combined total of 25 cases with IMD, 18 (72%) showed Ig G kappa and Ig G lambda biclonal bands and 7 (28%) other monoclonal Ig, respectively. There was no case of different light chain only gammopathy. At the time of IMD following the 1st transplant, 2 showed normal and 16 abnormal FLC assays. Of the 16, 3 showed different types of predominant light chains from that of the diagnosis, and 13 similar types. Following the 2nd transplant, all 7 cases showed similar type of light chains. Of the 25 cases of IMD in the combined 76 cases of transplant, 22 cases were associated with the similar type of light chains whereas there were only 3 cases (12%) of different light chain predominance. There was no case of a different type of predominant light chain associated with the non-IMD cases (Fisher's Exact test, p = 0.01). Of the 22 cases of IMD associated with the similar type of light chain, 5 (20%) showed transient elevations in the light chain level > 2 x the pre-IMD values, with the median duration of elevations of 28 (range 7 to 64) days. The current study suggests that if IMD is suspected following transplant by SPEP, careful observation for at least a month but no immediate re-evaluation of disease status may be indicated even when the type or level of light chain changed. Further study is necessary to confirm the findings. DisclosuresMyint:Seattle Genetics, Inc.: Research Funding.

A346 Prospective Study of Serum FLC and Other M-Protein Assays: When and How to Measure Response?

A346 Prospective Study of Serum FLC and Other M-Protein Assays: When and How to Measure Response?

Guidelines on the diagnosis and management of multiple myeloma 2005

In 2001, guidelines for the diagnosis and management of myeloma were published by the Guidelines Working Group of the UK Myeloma Forum (UKMF) on behalf of the British Committee for Standards in Haematology (BCSH) (UK Myeloma Forum; British Committee for Standards in Haematology, 2001). That same year, the second edition of guidelines prepared by the Nordic Myeloma Study Group (NMSG) in 1995 was issued (in the Scandinavian languages; http:// www.myeloma-nordic.org). As both sets of guidelines were intended to be evidence based, it was reassuring to note that the recommendations were similar. Subsequently, informal contact between members of the two groups led to the decision to prepare these common, updated guidelines. These revised and updated guidelines include new sections on imaging and the management of skeletal disease, cover new developments in disease classification and staging and the use of new therapeutic approaches, such as thalidomide, bortezomib and reduced-intensity allogeneic transplantation. The guidelines are presented in specific sections as follows:

The tumor kinetics of multiple myeloma following autologous stem cell transplantation as assessed by measuring serum-free light chains

In multiple myeloma, changes in serum-free immunoglobulin light chains (FLC) are a more rapid indicator of treatment response than intact immunoglobulin due to their shorter serum half-life. The present study analysed the changes in serum FLC after autologous peripheral blood stem cell transplantation (PBSCT) in 19 patients. The majority of myeloma patients (18 of 19) undergoing PBSCT had a rapid fall in FLC concentrations. In all 11 of 19 patients with raised tumor FLC, it fell within 48 h following high-dose melphalan. In patients with monoclonal intact immunoglobulin, the tumor FLC fell quicker (median half-life 4.3 days) than the monoclonal intact immunoglobulin (median half-life 14 days). FLC recovery occurred after (13 of 19) or around the time of neutrophil engraftment (6 of 19). With a median follow up of 220 days post-transplant, 16 of 19 patients have a normal FLC ratio and 3 of 19 have an elevated tumor FLC/abnormal ratio. FLC assays provided a sensitive monitor of changes in tumor and non-tumor plasma cells after PBSCT. This assay is potentially valuable as a marker of chemosensitivity, as an indicator of residual tumor and indicated time to lymphocyte engraftment. Further follow-up is required to ascertain whether differences in the kinetics of FLC responses have any prognostic clinical utility.

Serum free light chain immunoassays and their clinical application

Measurement of urine free light chains (flc) is important for assessing monoclonal plasma cell diseases. However, since the kidneys metabolize large amounts of flc, urine concentrations may not accurately reflect plasma cell synthesis. From a theoretical viewpoint, serum measurements would be preferable, just as blood glucose measurements are preferable to urine measurements for managing patients with diabetes mellitus. Unfortunately, the development of satisfactory serum flc immunoassays has been hampered by the lack of specific, high-affinity antisera. Recent publications indicate that this situation has now changed. Serum flc have been quantified using routine clinical laboratory instruments and have produced useful diagnostic results in several diseases. Thus, 100% of patients with light-chain multiple myeloma, 75% of patients with nonsecretory myeloma and more than 95% of patients with primary amyloidosis could be diagnosed using serum flc assays. This improvement in disease detection rates and the potential for superior disease monitoring may obviate the need for urine flc tests in most patients with monoclonal plasma cell diseases.