The role of minimal residual disease and serum free light chain ratio in the management of multiple myeloma.

Multiple myeloma (MM) denotes a cancerous growth characterized by abnormal proliferation of plasma cells. Growing evidence suggests that the complexity in addressing MM lies in the presence of minimal residual disease (MRD) within the body. MRD assessment is becoming increasingly important for risk assessment in patients with MM. Similarly, the levels of serum free protein light chain and their ratio play a crucial role in assessing the disease burden and changes in MM. In this paper, we review and explore the utilization of MRD and serum free light chain ratio in the treatment of MM, delving into their respective characteristics, advantages, disadvantages, and their interrelation.

[The Value of sFLC and Serum Calcium in the Diagnosis and Prognosis of Multiple Myeloma Patients].

OBJECTIVE: To investigate the value of serum free light chain (sFLC) and serum calcium ion in the diagnosis and prognosis of multiple myeloma (MM). METHODS: Forty patients with MM treated in Henan Provincial People's Hospital from January 2018 to January 2022 were selected as the observation group, and 40 healthy volunteers were selected as the control group. The differences of sFLC-κ、sFLC-λ、sFLC-κ/λ, serum calcium ions, etc between the two groups were compared. Meanwhile, the differences of sFLC-κ、sFLC-λ、sFLC-κ/λ, serum calcium ions, etc in different international staging systems (ISS), chemotherapy efficacy and prognosis patients were analyzed. RESULTS: The levels of sFLC-κï¼»(98.39±21.19) vs (12.01±4.45) mg/Lï¼½, sFLC-λï¼»(210.20±45.54) vs (14.10±5.11) mg/Lï¼½ and proportions of hypocalcemia （65% vs 0） in the observation group were significantly higher than those in the control group (P < 0.05), while sFLC-κ/ λ ratio［（0.44±0.10） vs (0.87±0.12)ï¼½ and serum calcium ions ［（1.98±0.46） vs （2.42±0.40）mmol/Lï¼½ were significantly lower than those in the control group (P < 0.05). The sFLC-κ, sFLC-λ, the proportion of hypocalcemia and the course of hypocalcemia in ISS stage III patients in the observation group were significantly higher than those in stage I and II patients (P < 0.05), while sFLC-κ/λ ratio, and serum calcium ions were significantly lower than those in stage I and II patients (P < 0.05). The levels of sFLC-κ ［（107.76±21.22） vs （94.67±20.11）mg/Lï¼½, sFLC- λ［（245.54±41.12） vs （205.54±50.22）mg/Lï¼½ of patients with hypocalcemia in the observation group was significantly higher than those without hypocalcemia (P < 0.05), while the sFLC-κ/λ ratio was significantly lower than those without hypocalcemia ［（0.42±0.04） vs （0.47±0.06）；P < 0.05ï¼½. The levels of sFLC-κ ï¼»(107.29±20.14） vs （ 91.11±18.92）mg/Lï¼½, sFLC-λ［（247.98±42.26） vs （179.29±39.32）mg/Lï¼½ in patients with ineffective chemotherapy were significantly higher than those in patients with effective chemotherapy (P < 0.05), while the sFLC-κ/λ ratio was significantly lower than those in patients with effective chemotherapy ï¼»(0.43±0.10) vs (0.50±0.09)；P < 0.05）］. The area under the ROC curve for sFLC-κ, sFLC-λ, sFLC-κ/λ predicting ineffective chemotherapy was 0.803, 0.793 and 0.699 respectively, P < 0.05. There was no significant difference in sFLC-κ, sFLC-λ, sFLC-κ/λ ratio, serum calcium ion, hypocalcemia ratio and hypocalcemia course between survival and death patients (P >0.05). CONCLUSION: sFLC and serum calcium are related to ISS stage of MM patients. sFLC level has a certain value to predict the curative effect of chemotherapy in MM patients. However, the prognostic values of sFLC and serum calcium are not yet confirmed for MM patients.

[Clinical Significance of Serum Free Light Chain in Monoclonal Gammopathy].

OBJECTIVE: To investigate the expression and clinical significance of serum free light chain (sFLC) in patients with monoclonal gammopathy (MG). METHODS: The peripheral blood of 98 patients with MG and 30 healthy volunteers were collected. The level of sFLC was detected by immunoturbidimetry, and the value of sFLC in diagnosis, disease severity, and efficacy evaluation was analyzed. RESULTS: Among 98 MG patients, there were 58 males and 40 females, 45 cases of monoclonal gammopathy of renal significance (MGRS), 33 cases of monoclonal gammopathy of undetermined significance (MGUS), 20 cases of hematological malignancy (HM), 58 cases of IgG type, 26 cases of IgA type, 7 cases of IgM type, 5 cases of light chain type, 2 cases of non-secreting type, 35 cases of κ type, 63 cases of λ type, 53 cases of renal insufficiency, 45 cases of normal renal function. The expression levels of sFLC-κ and sFLC-λ in MG patients were significantly higher than those of the control group (P <0.01). The expression levels of sFLC-κ and sFLC-λ in HM patients were significantly higher than MGRS and MGUS patients, and in MGRS patients were also significantly higher than MGUS patients (P <0.05). Patients with abnormal renal function had higher expression levels of sFLC-κ and sFLC-λ than patients with normal renal function (P <0.01). sFLC-κ and sFLC-λ were positively correlated with the expression level of globulin (r =0.392, r =0.435) and ß2-MG (r =0.403, r =0.468) in MG patients, as well as serum creatinine in patients with abnormal renal function (r =0.586, r =0.631), while no significant correlation was found with age, sex, albumin, lactate dehydrogenase, and serum calcium. After treatment, the levels of sFLC-κ and sFLC-λ were significantly decreased (P <0.01). CONCLUSION: sFLC is significantly elevated in MG patients and can be quickly detected with high sensitivity, which is helpful for the diagnosis of disease type, judgment of disease severity, and evaluation of therapy.

Data analytics improves the diagnostic accuracy of serum free light chain results for detecting monoclonal gammopathy.

OBJECTIVES: To evaluate the real-world performance and reference intervals of the Binding Site Freelite serum free light chain (SFLC) assay (Thermo Fisher Scientific), a global standard for diagnosis, prognostication, and response assessment for monoclonal gammopathies. METHODS: An informatics-based approach was used to retrospectively evaluate concordance between SFLC and the orthogonal Sebia HYDRASYS immunofixation assay results in a large clinical data set consecutively reported between 2010 and 2020. RESULTS: Among patients with monoclonal-negative results by both SFLC and Sebia HYDRASYS immunofixation assays, 25% (1226/5057) had κ/λ ratios (KLRs) outside the manufacturer-defined and International Myeloma Working Group-cited normal reference interval of 0.26 to 1.65. These results were consistent over the study period and were not affected by sex, age, impaired kidney function, or assay antisera lot variation. Assay drift, in addition to other potential factors, affected the KLR distribution. Using International Statistical Classification of Diseases (ICD) codes, kidney function data, and the central 95% of KLR values generated on the Optilite platform (Thermo Fisher Scientific), we derived a new reference interval of 0.67 to 2.13, reducing the KLR false-positive rate to 8%. However, normal KLR persisted among 16% (14/85) of samples with free λ chains by immunofixation, warranting caution during interpretation. CONCLUSIONS: Our analysis indicated that revision of Freelite SFLC reference intervals improves assay interpretation and should prompt reconsideration of Freelite reference intervals worldwide.

[The Expression Level and Diagnostic Value of Serum Free Light Chain in B-Cell Non-Hodgkin Lymphoma].

OBJECTIVE: To investigate the expression level and the diagnostic value of serum free light chain in B-cell non-Hodgkin's lymphoma (B-NHL). METHODS: We retrospectively analyzed the results of serum free light chain (sFLC) of 394 newly treated B-NHL patients in our hospital from January 2014 to December 2021 and compared the secretion levels of sFLC among different subtypes of B-NHL. The value of sFLC secretion levels in the diagnosis of WM was evaluated using ROC. RESULTS: Increased proportion of sFLC, abnormal ratio of sFLC (κ / λ) and the secretion levels of sFLC (κ+λ) were different in different B-NHL subtypes, Waldenstrom's macroglobulinemia (WM) had the highest proportion of elevated sFLC(82.68%) and abnormal sFLC(κ/ λ)(87.0%), the proportion of FL(18.0%) and DLBCL patients(12.8%) with elevated sFLC was lower (P<0.05). The expression levels of sFLC can helpful in the diagnosis of WM (AUC=0.874，P<0.001， 95% CI: 0.779-0.970). At the same time, higher sFLC levels and sFLC cloning patterns predicted the possibility of bone marrow infiltration of lymphoma. CONCLUSION: The serum free light chains is common in patients with B-NHL. The elevated level and type of free light chain are associated with the type of lymphoma, and the patients with bone marrow infiltration have higher sFLC（κ+ λ） expression level.

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.

Retrospective analysis of serum free light chain reference intervals and risk for monoclonal gammopathy suggests different limits than those in international guidelines.

OBJECTIVES: Recent reference interval studies of the serum free light chain (FLC) test using contemporary instruments display divergence with the diagnostic range generally adopted as the international standard. In this study, we perform a retrospective reference interval analysis with risk predictions for monoclonal gammopathy. METHODS: Retrospective laboratory and clinical data for 8,986 patients were included in the study. Reference intervals were generated against a set of inclusion/exclusion criteria for two time periods representing the use of different instruments. The presence of monoclonal gammopathy was established from diagnostic test interpretations and EHR diagnosis codes in the patient problem lists and medical history. RESULTS: The 95% FLC ratio reference intervals were 0.76-2.38 for SPAPLUS®, and 0.68-1.82 for Optilite® instruments. These intervals varied considerably from the current diagnostic range of 0.26-1.65 and mapped approximately to the FLC ratios beyond which risk of monoclonal gammopathy substantially increased. CONCLUSIONS: These findings corroborate recent reference interval studies and support recommendations for independent re-evaluation of intervals by institutions as well as an update of international guidelines.

Urine Protein Immunofixation Electrophoresis: Free Light Chain Urine Immunofixation Electrophoresis Is More Sensitive than Conventional Assays for Detecting Monoclonal Light Chains and Could Serve as a Marker of Minimal Residual Disease.

BACKGROUND: Immunoglobulin monoclonal light chains (MLCs) in serum and urine are markers for monoclonal gammopathy and could serve as markers of minimal residual disease (MRD) in multiple myeloma (MM). Excretion of MLCs in urine is known to result in renal damage and shorter survival in patients with LC-predominant MM. METHODS: Retrospective review of urine immunofixation in 1738 specimens at 3 medical centers was conducted to assess the utility of urinalysis for diagnosis and monitoring of monoclonal gammopathy. We tested 228 stored urine specimens via the modified urine immunofixation method, using antisera to assay free LCs (FLCs). RESULTS: Our review of urine immunofixation results and medical records validated the theory that the only meaningful value-added finding was detection of monoclonal free light chains. Examination of 228 urine specimens using our novel method revealed 18.4% additional positive results. The rate of incremental findings for lambda LCs was nearly 3-fold higher than for kappa LCs. CONCLUSIONS: The new method of urine immunofixation is significantly more sensitive and more efficient than the conventional method for detecting MLCs in urine. The new assay appears to be sensitive enough to prove that MLCs serve as a marker of MRD in MM.

Evaluation of laboratory diagnostic tests for light-chain clonality and bone marrow findings in AL amyloidosis.

Background: Light-chain amyloidosis (AL) is the most common form of systemic amyloidosis. This study aimed to evaluate the usefulness of laboratory tests for light-chain clonality and bone marrow (BM) findings in AL amyloidosis. Methods: We retrospectively enrolled patients newly diagnosed with AL amyloidosis on pathological examination who underwent a BM biopsy. Laboratory test data for light-chain clonality were collected and compared. Amyloid deposits were identified with H&E, Congo red, and PAS stains. Results: We reviewed 98 patients with AL amyloidosis. Light chain clonality (λ, 64 cases; κ, 34 cases) was detected by serum immunofixation electrophoresis (IFE) (63.3%), urine IFE (70.8%), serum protein electrophoresis (PEP) (44.9%), urine PEP (44.8%), serum free light chain (SFLC) ratio (79.5%), and BM immunohistochemistry (IHC) (85.7%). Flow cytometric (FCM) assay identified aberrant BM plasma cells in 92.9% of cases. BM amyloid deposits were identified in 35 of the 98 cases (35.7%); 71.4% (25/35) were Congo red-positive, and 100.0% (35/35) were PAS-positive. Conclusion: Laboratory tests for detecting light-chain clonality in AL amyloidosis in order of sensitivity include FCM assay for aberrant plasma cells, IHC for light chains on BM biopsy or clot section, SFLC ratio, and serum and urine IFE. Congo red staining of BM samples remains an important tool for identifying amyloid deposits in BM. Periodic acid-Schiff (PAS) staining can be useful in diagnosing some cases of Congo red-negative amyloidosis.

The Expression Level and Diagnostic Value of Serum Free Light Chain in B-Cell Non-Hodgkin Lymphoma / 中国实验血液学杂志

OBJECTIVE@#To investigate the expression level and the diagnostic value of serum free light chain in B-cell non-Hodgkin's lymphoma (B-NHL).@*METHODS@#We retrospectively analyzed the results of serum free light chain (sFLC) of 394 newly treated B-NHL patients in our hospital from January 2014 to December 2021 and compared the secretion levels of sFLC among different subtypes of B-NHL. The value of sFLC secretion levels in the diagnosis of WM was evaluated using ROC.@*RESULTS@#Increased proportion of sFLC, abnormal ratio of sFLC (κ / λ) and the secretion levels of sFLC (κ+λ) were different in different B-NHL subtypes, Waldenstrom's macroglobulinemia (WM) had the highest proportion of elevated sFLC(82.68%) and abnormal sFLC(κ/ λ)(87.0%), the proportion of FL(18.0%) and DLBCL patients(12.8%) with elevated sFLC was lower (P<0.05). The expression levels of sFLC can helpful in the diagnosis of WM (AUC=0.874，P<0.001， 95% CI: 0.779-0.970). At the same time, higher sFLC levels and sFLC cloning patterns predicted the possibility of bone marrow infiltration of lymphoma.@*CONCLUSION@#The serum free light chains is common in patients with B-NHL. The elevated level and type of free light chain are associated with the type of lymphoma, and the patients with bone marrow infiltration have higher sFLC（κ+ λ） expression level.

Case of non-secretory multiple myeloma eventually diagnosed by 18F-FDG PET/CT.

Non-secretory multiple myeloma (NSMM) is a rare type of multiple myeloma characterized by the absence of the M protein, making its diagnosis challenging. Here, we report a 67-year-old female patient eventually diagnosed as NSMM with positron emission tomography-computed tomography (PET/CT) imaging as a clue.

A Cohort Study of Free Light Chain Ratio in Combination with Serum Protein Electrophoresis as a First-Line Test in General Practice.

Multiple Myeloma (MM) often present with unspecific symptoms, which can lead to diagnostic delay. Serum-free light chain (sFLC) ratio is suggested to replace urine protein electrophoresis (UPE) in the diagnostic work-up of myeloma. We aimed to investigate the performance of the sFLC-ratio in general practice (GP) compared to UPE, just as we explored different sFLC-ratio cut-offs' influence on diagnostic values. In a cohort of 13,210 patients from GP measures of sFLC-ratio, serum protein electrophoresis (SPE), or UPE were compared to diagnoses of incident M-component related diseases acquired from Danish health registers. UPE and sFLC-ratio equally improved diagnostic values when combined with SPE (sensitivity: SPE and UPE: 95.6 (90.6-98.4); SPE and sFLC-ratio: 95.1 (90.2-98.0)). The addition of the sFLC-ratio to SPE resulted in the identification of 13 patients with MGUS, light chain disease and amyloidosis, which was in line with the addition of UPE to SPE. The number of false-positive tests was UPE and SPE: 364 (11%) and sFLC-ratio and SPE: 677(19%). Expanding sFLC-ratio reference range to 0.26-4.32 resulted in a significant reduction in false positives n = 226 (6%) without loss of patients with clinical plasma cell dyscrasias. sFLC-ratio improves the diagnostic value of SPE in GP. However, due to low specificity and a large number of false positives, expanded cut-off values should be considered.

Comparison of clinical and laboratory characteristics of nonsecretory multiple myeloma and secretory multiple myeloma in a tertiary care hospital.

INTRODUCTION: Nonsecretory multiple myeloma (NSM) is a rare variant of multiple myeloma, accounting for approximately 1%-5% of all reported cases. We compared the characteristics of NSM and secretory multiple myeloma (SM). METHODS: We examined clinical and laboratory characteristics of 17 patients diagnosed with NSM and 40 patients diagnosed with SM. NSM was diagnosed based on findings of bone marrow (BM) examination, serum-free light chain (sFLC) assay, flow cytometric (FCM) immunophenotyping, chromosomal analysis, and imaging studies. RESULTS: No patient with NSM had hypercalcemia or renal insufficiency at diagnosis. Patients with NSM were less anemic (p < .05) but had higher lactate dehydrogenase levels (p < .05) than patients with SM. In addition, patients with NSM had a lower percentage of plasma cells in the BM, confirmed by manual differential count (p < .05) and FCM immunophenotyping (p < .05). The sFLC ratio in patients with NSM was abnormal (15/17, 88.2%) and was lower than that in patients with SM (p < .05). Risk stratification in Revised International Staging System revealed a low-risk tendency in patients with NSM (p = .235). CONCLUSION: NSM patients showed different clinical and laboratory characteristics from SM patients. FCM immunophenotyping and sFLC assay particularly had differences between NSM patients and SM patients. Thus, they are essential for diagnosing NSM.

Comparative analysis of three serum-free light-chain detection systems in the diagnosis of multiple myeloma.

OBJECTIVE: To observe the comparability of serum-free light chain (sFLC) detected by Beckman, Siemens, and Binding Site. METHODS: In this study, 110 patients who were diagnosed with multiple myeloma in State Key Laboratory of Experimental Hematology from November 2019 to August 2020. According to the instructions of equipment and reagent manufacturers, three detection systems (Binding Site, Beckman, and Siemens) were used to detect the serum-free light chain of selected analysis samples. Meanwhile, sFLC test results of the three instruments were compared. According to EP9-A3 guide, correlation and consistency were conducted by Bland-Altman and Passing-Bablok regression. RESULTS: The free kappa light-chain serum samples and the free lambda light-chain samples were quantitatively analyzed by the three systems. Binding Site, Beckman, and Siemens free light-chain detection results were as follows: FLC-κ: 42.23 (3.73, 423), 34.55 (6.5, 194), 39.85 (3.73, 423); FLC-λ: 31.46 (1.39, 8180.42), 32 (4.3, 275), 37.65 (2.28, 526); rFLC (FLC-κ/FLC-λ): 1.21 (0, 131.28), 0.96 (0.02, 43.49), 1.04 (0.04, 40.29). The Kappa valuation of FLC-κ between Beckman and Binding Site is 0.97, Kappa valuation of FLC-λ between Beckman and Binding Site is 0.96, Kappa valuation of rFLC between Beckman and Binding Site is 0.97. The Kappa valuation of FLC-κ between Siemens and Binding Site is 0.96, Kappa valuation of FLC-λ between Siemens and Binding Site is 0.88, Kappa valuation of rFLC between Siemens and Binding Site is 0.94. CONCLUSION: All of the three systems can meet the needs of diagnosis and treatment in clinical application. These analyses showed a very good concordance between Beckman, Siemens, and Binding Site.

Prognostic Impact of Serum Free Light Chain Ratio Normalization in Patients with Multiple Myeloma Treated within the GMMG-MM5 Trial.

We investigated the prognostic impact of time-dependent serum free light chain ratio (FLCr) normalization in 590 patients with secretory multiple myeloma (MM) during first-line treatment within the German-Speaking Myeloma Multicenter Group MM5 trial. Serum free light chains (sFLC) were assessed by the Freelite test at baseline, after induction, mobilization, autologous blood stem cell transplantation, consolidation and every three months during maintenance or follow up within two years after the start of maintenance. The proportion of patients with a normal or normalized FLCr increased from 3.6% at baseline to 23.2% after induction and 64.7% after consolidation. The achievement of FLCr normalization at any one time before the start of maintenance was associated with significantly prolonged progression-free survival (PFS) (p < 0.01, hazard ratio (HR) = 0.61, 95% confidence interval (95% CI) = 0.47-0.79) and overall survival (OS) (p = 0.02, HR = 0.67, 95% CI = 0.48-0.93) in multivariable time-dependent Cox regression analyses. Furthermore, reaching immune reconstitution, defined as the normalization of uninvolved immunoglobulins, before maintenance was associated with superior PFS (p = 0.04, HR = 0.77, 95% CI = 0.60-0.99) and OS (p = 0.01, HR = 0.59, 95% CI = 0.41-0.86). We conclude that FLCr normalization during therapy is an important favorable prognostic factor in MM. Therefore, we recommend serial measurements of sFLC during therapy until achieving FLCr normalization, even in patients with secretory MM.

Involved free light chain: an early independent predictor of response and progression in multiple myeloma.

Serum and urine protein electrophoresis (sPEP/uPEP) are the standard methods for monitoring of multiple myeloma (MM). However, a method of detection with shorter half-life, such as serum-free light chain (FLC), could detect the response or progression earlier. In total, 450 MM patients were assessed in first, second, and third line. Response and progression were classified according to International myeloma working group guidelines. The overall median time to partial response or better was detectable significantly earlier with involved free light chain (iFLC) 1.94 months (IQR: 1.61-2.23) compared to sPEP 5.39 months (IQR: 3.88-7.00). In first line, iFLC detected progression earlier compared to sPEP, particularly in patients with progression more than 18 months after best response. In conclusion, a response observed by iFLC occurs at least a median of 3 months before response is detected by sPEP/uPEP.

Idiopathic Hypercalcemia in Decompensated Cirrhosis: Reexploring an Entity in Oblivion.

Hypercalcemia is a rare metabolic abnormality seen in patients with cirrhosis and is usually considered a paraneoplastic manifestation of hepatocellular carcinoma. Idiopathic hypercalcemia in cirrhosis is a diagnosis of exclusion, which is considered when all the causes of hypercalcemia have been ruled out. Here, we report a rare case of idiopathic hypercalcemia presenting as acute kidney injury in a case of decompensated cirrhosis, managed with adequate hydration and injection of ibandronate and intranasal calcitonin, leading to the normalization of serum calcium and resolution of acute kidney injury.

Serum free light chain reference intervals in an Optilite and their influence on clinical guidelines.

BACKGROUND: Serum free light chain (FLC) analysis has been incorporated into the International Myeloma Working Group guidelines for the diagnosis and management of all monoclonal gammopathies. These recommendations were solely based on a single assay method (Freelite assay) and instrument. Here, we establish new reference intervals (RIs) for kappa and lambda FLC and the kappa-lambda difference and sum and a new diagnostic range for kappa/lambda FLC ratio (K/L-FLC) in an Optilite turbidimeter (The Binding Site) with the Freelite assay. METHODS: To establish new RIs, the CLSI EP28-A3C protocol was applied to 249 sample blood donors from Fuenlabrada, Spain, and the central 95% and total range were estimated. Samples from patients with polyclonal hypo- and hypergammaglobulinemia were used for the evaluation of K/L-FLC as a monoclonal proliferation index. RESULTS: The new RIs and the new K/L-FLC diagnostic range for the Optilite (0.65-2.56 mg/L) are very different from those in on the guidelines (0.26-1.65 mg/L). We propose new RIs for the K - L difference and the K + L sum. Diagnostic range validation as a monoclonal proliferation index with samples with hypo- and hypergammaglobulinemia confirms this new range. CONCLUSIONS: In this study, we present the FLC RI for Freelite reagents measured on an Optilite turbidimeter. These ranges are different from those provided by the manufacturer and from those used in most studies in the literature, which may lead to patient misclassification. Manufacturers and clinical laboratories must strive to provide RIs for the technology they are using and for their population.

Evaluation of Correlation between Serum Free Light-Chain Assay and Bone Marrow Study in Multiple Myeloma Patients.

Background: Multiple myeloma is a hematologic malignancy manifested by the secretion of abnormal immunoglobulin. Different methods have been described for diagnosis and patient response to management. Serum free light-chain assay is recently approved in the diagnosis of multiple myeloma patients. This study aimed to evaluate the diagnostic accuracy of serum free light-chain assay and its agreement to bone marrow findings. Materials and Methods: Forty-six patients with the diagnosis of multiple myeloma were enrolled in the study. The patients were grouped into newly diagnosed cases (22 patients,47.8%) and known cases who were under treatment (24 patients,52.2%). Bone marrow study was done and percentage and clonal status of plasma cells were evaluated by a combination of immunohistochemistry and flow cytometry. Free light-chain assay was done in all patients and sensitivity, specificity, positive predictive value, and negative predictive value were analyzed. Results: Thirty of 46 patients showed monoclonal plasma cell infiltration and 16 patients showed polyclonal plasma cell infiltration based on bone marrow findings. An abnormal κ/λ ratio was seen in 15(68.18%) of new cases and 16(66.6%) of known cases. Sensitivity, specificity, PPV and NPV for κ/λ ratio were 72.73%, 46.15%, 71%, and 50%, respectively. Conclusion: In conclusion, due to high false positive and false negative results, the presence of an abnormal serum FLC ratio was not equal to the presence of monoclonal gammopathy, and observation of a normal ratio does not exclude the presence of monoclonal gammopathy.