Detection of kappa and lambda light chain monoclonal proteins in human serum: automated immunoassay versus immunofixation electrophoresis

Recently, turbidimetric immunoassays for detecting and quantifying kappa and lambda free light chains (FLC) have become available and are promoted as being more sensitive than immunofixation electrophoresis (IFE) in detecting FLC monoclonal proteins. In this study, we assessed the ability of these turbidimetric assays to detect serum monoclonal proteins involving both free and heavy-chain-bound kappa and lambda light chains compared to standard immunofixation electrophoresis. Sera demonstrating a restricted band of protein migration (other than a definite M spike) by serum protein electrophoresis (SPE), which may represent early monoclonal proteins, were also examined. When compared to IFE, percent agreement, sensitivity, and specificity for the kappa-FLC and lambda-FLC were 94.6, 72.9, and 99.5% and 98.5, 91.4, and 99.7%, respectively, in detecting monoclonal proteins involving free and heavy-chain-bound light chains. The majority of sera (73.7%) demonstrating a restricted band of protein migration on SPE demonstrated abnormal IFE patterns suggestive of multiple myeloma or monoclonal gammopathy of unknown significance, but gave normal kappa/lambda FLC ratios using the turbidimetric immunoassays. In conclusion, the kappa and lambda FLC assays are significantly less sensitive (72.9 to 91.4%) than IFE, but specific in detecting serum monoclonal proteins. Moreover, the kappa/lambda ratio has little value in routine screening since the majority of sera with abnormal IFE patterns had normal kappa/lambda FLC ratios.     

Laboratory characterizations on 2007 cases of monoclonal gammopathies in East China

Monoclonal gammopathies are characterized by the presence of monoclonal immunoglobulin in patients with or without evidence of multiple myeloma （MM）, macroglobulinemia, amyloidosis （AL）, or a related plasma cell proliferative disorder. This study aims to evaluate laboratory diagnostic characters of monoclonal gammopathies and investigates the correlation between monoclonal gammopathies and transforming growth factor β1 （TGFβ1）. Immunofixation electrophoresis （IFE）, serum protein electrophoresis （SPE）, nephelometry and urine light chain ELISA were used for laboratory identification of monoclonal immunoglobulins. Plasma TGFβ1 was detected with double-antibodies ELISA. Lightcycler was used for single nucleotide polymorphism （SNP） analysis. Totally 2,007 cases of monoclonal immunoglobulin （M protein） were identified in 10,682 samples. The isotypes of M protein were IgG type 47.1%, IgA 23.0%, IgM 8.7%, IgD 5.3%, free light chain κ 6.1%, λ 9.8%. In reference to IFE, the coherency of diagnosis was serum light chain ratio （κ/λ） 94.4%, quantitation of Igs 83%, light chain quantitation 80.9%, and urine light chain ratio （κ/λ） 58.0%. Plasma TGFβ1 was elevated significantly compared to normal control. The allelic frequency of codon 10 （C 〉 T） was neither associated with the existence of the M protein nor with the M protein isotype. Monoclonal gammopathies can be identified with the combination of IFE, SPE, Igs quantitaion and urine light chain determination. Although TGFβ1, an important cytokine in immune regulation, was elevated in monoclonal gammopathies, the SNPs in coding region of TGFβ1 gene did not confer susceptibility to the development of monoclonal gammopathies in this study. Cellular ＆ Molecular Immunology. 2008;5（4）： 293-298.     

Extended use of serum free light chain as a biomarker in lymphoproliferative disorders: a comprehensive review

Serum free light chain (sFLC) assays were shown to improve detection, management, and prognostication in plasma cell disorders. Recently, sFLC assays improved detection of M proteins when combined with standard methods of protein electrophoresis/immunofixation in patients with non-Hodgkin lymphoma/chronic lymphocytic leukemia (NHL/CLL). Incidence of abnormal sFLC ratio (sFLCr) varied from 0% to 36% and 29.7% to 59% in NHL and CLL, respectively. Increased sFLC levels or abnormal sFLCr predict shorter overall survival in early-stage CLL. Furthermore, abnormal sFLCr correlated with advanced disease stage and poorer outcome. In diffuse large B-cell lymphomas, increased sFLC was demonstrated as an independent, adverse prognostic factor for overall/event-free survival. Moreover, abnormal sFLCr can be a diagnostic tool in central nervous system lymphomas. Finally, the quantitative FLC assay has the potential to become a new, easily measured biomarker for predicting prognosis and enhanced detection in NHL/CLL. It may be used serially at follow-up evaluations to provide clues to relapse.     

Immunoglobulin G, A, and M Light Chain Ratios in some Humoral Immunological Disorders

The total kappa/lambda immunoglobulin light chain ratio and the kappa/lambda ratios within each of the serum immunoglobulin classes G, A, and M were measured in thirteen patients with humoral immunological disorders. Of those patients, eight had common variable immunodeficiency whereas five patients had other forms of humoral immunological deficiencies. Eleven patients had abnormal antibody response in vivo. All but three of the thirteen patients had clearly abnormal light chain ratios in one or more of the immunoglobulin classes. We conclude that humoral immunological disorders, usually characterized by abnormal heavy chain production and a disturbed antibody response, may frequently have a concomitant abnormal synthesis of the light chains resulting in an abnormal kappa/lambda light chain ratio.     

Atypical imaging feature of non-secretory multiple myeloma

Non-secretory multiple myeloma (NSMM) is a rare variant of the classic form of multiple myeloma in which no monoclonal gammopathy can be demonstrated in the serum or urine. We describe a rare case of non-secretory multiple myeloma in a 23 year old female presenting with bilateral limb weakness of two years duration. Clinically she was diagnosed to have Pott's spine and was treated with category 1 anti tubercular drugs. Hematological investigations showed plasmacytosis and radiography showed osteolytic lesions. No monoclonal gammopathy was found in the serum or urine. MRI showed multiple compressions with sclerosis within vertebral bodies suggestive of osteomalacia/ diffuse infiltrative disorder. The free light chain (FLC) assay revealed increment in the free kappa light chain and an abnormal κ/λ ratio. Free Light Chain assay (FLC) when used in complement with Protein Electrophoresis (PEP) and Immunofixation Electrophoresis (IFE) were pivotal in diagnosis of non secretory multiple myeloma or light chain myelomas. FLC is a useful monitoring tool because it reflects therapy results due to short serum half life.     

Immunocytochemical detection of kappa and lambda light chain V region subgroups in human B-cell malignancies.

We have used a sensitive immunoperoxidase method and highly specific anti-light chain antisera to determine the light chain variable region (VL) subgroup nature of cytoplasmic (c) and cell surface (s) Ig expressed by human monoclonal plasma cells and B lymphocytes. The immunocytochemical characterization of cIg and sIg used antisera specific for the established kappa light chain V kappa subgroups (V kappa I, V kappa II, V kappa III, and V kappa IV) and the lambda light chain V lambda subgroups (V lambda I, V lambda II/V, V lambda IV, and V lambda VI). Studies were performed using cytospin preparations of bone marrow-, peripheral blood-, and lymph node-derived cells from patients with multiple myeloma, amyloidosis AL, and Waldenström''s macroglobulinemia and with low-, mid-, and high-grade B-cell malignancies. The V kappa or V lambda subgroup of the cIg or sIg also could be identified after deparaffinization and enzyme treatment of formalin-fixed, paraffin-embedded specimens. For those patients who had monoclonal serum or urinary Igs, there was complete concordance between the VL subgroup of the secreted Ig and that of the cIg or sIg. The percentage distribution of V kappa or V lambda subgroups on the sIg of cells from patients with chronic lymphocytic leukemia (CLL) and other cytomorphologic types of B-cell malignancies differed from that found for kappa- or lambda-type Bence Jones proteins obtained from patients with multiple myeloma, amyloidosis AL, and Waldenström''s macroglobulinemia. In contrast to the plasma cell and lymphocytoid plasma cell diseases, a relative predominance of certain VL subgroups, ie, V kappa IV, V lambda III, and V lambda IV, and the absence of the amyloid-associated V lambda VI subgroup were found in CLL and related diseases. The immunocytochemical techniques used make possible a rapid means to demonstrate B-cell monoclonality and provide further evidence for the selective expression of certain VL genes in human B-cell neoplasia.     

Immunodiagnostic capabilities of anti-free immunoglobulin light chain monoclonal antibodies

Overproduction of plasma cell-derived monoclonal free kappa or lambda immunoglobulin light chains (FLCs) is a hallmark of multiple myeloma, AL amyloidosis, and light chain deposition disease. Because these components serve as unique cellular and serologic biomarkers, their detection and quantitation has diagnostic, therapeutic, and prognostic import. In this regard, we have developed monoclonal antibodies (mAbs) that specifically recognize the kappa or lambda FLC products of all known human variable and constant region light chain genes. We now report the results of our studies that have demonstrated the capability of these reagents to measure, in a modified fluid-phase capture enzyme-linked immunosorbent assay (ELISA), serum kappa and lambda FLCs at concentrations as low as 5 and 15 ng/mL, respectively. The mAb-based ELISA has greater sensitivity and reproducibility than does the commercially available immunoturbidimetric assay that uses polyclonal anti-FLC antibodies. In addition, the mAbs can immunostain monoclonal FLC-producing plasma cells and pathologic light chain-related amyloid and nonfibrillar tissue deposits. Our anti-FLC mAbs, with their high degree of reactivity and versatility, may provide an invaluable tool in the diagnosis and management of light chain-associated disease.     

Polyclonal free light chain of Ig may interfere with interpretation of monoclonal free light chain κ/λ ratio

There is controversy about whether a sensitive assay for the serum Ig free light chain (FLC) κ/λ ratio can replace urine immunofixation electrophoresis (UIFE). This report describes two untreated patients in whom monoclonal FLCs were identified in urine despite normal serum FLC κ/λ ratios. Unlike the classical serum electrophoretic patterns in multiple myeloma, both serum samples showed adequate amounts of polyclonal Ig. The most likely explanation is a masking effect by polyclonal FLC on the serum κ/λ ratio when sufficient concentrations of polyclonal FLC exist. These cases illustrate this likely effect and attest to the continued importance of UIFE for initial screening of patients for Bence-Jones protein.     

Proposed reference material for human free immunoglobulin light chain measurement

Human free immunoglobulin light chain (FLC) kappa and lambda are useful clinical markers for light chain myeloma and AL amyloidosis. With the recent development of specific and reliable FLC immunoassays, the quantitative measurement of FLCs will be widely used in clinical practice. However, researchers have used various calibrators, mainly monoclonal FLCs; thus, no standardization has been performed among the assay methods. This prompted us to purify intact FLCs from the pooled urine specimens of healthy volunteers as the first reference materials for FLC assays. After precipitation with ammonium sulfate, FLCs were purified by the following steps of chromatography; cation exchange, gel filtration, and antibody-assisted immunoaffinity. SDS-PAGE and Western blotting analyses showed that the purity of FLC kappa and FLC lambda was more than 98%. These purified FLCs did not contain the other immunological types of light chains. These intact and purified FLCs are suitable as the first reference materials to standardize FLC assays.     

Assessment of serum free light chain assays for plasma cell disorder screening in a Veterans Affairs population

This study evaluated serum kappa and lambda free light chain (FLC) concentrations in a Veterans Affairs (VA) population. We hypothesized that our older, mostly male, population should not differ in serum FLC ranges from levels previously established for younger male and female populations and that the assay would improve our screening protocol for plasma cell dyscrasias (PCD). Serum kappa and lambdaFLC were assayed in 312 consecutive serum samples collected during a 16-week period from veterans whose clinical presentation indicated a need for serum protein electrophoresis (SPEP) analysis. We reviewed our laboratory information system (LIS) files to evaluate the patients' diagnoses and treatment status in conjunction with serum FLC levels. All assays and validation studies were conducted using an immunoturbidimetric method with a Roche/Hitachi 911 modular analytical system. The intra-assay variability (CV) was <5%, based on 13 replicate assays of 4 control samples and 1 blank sample. Of the 312 patients, the SPEP results were normal in 235 and abnormal in 77. Of the 235 patients with normal SPEP results, 37 had abnormal FLC values and 20 of these were diagnosed as PCD. Of the 77 patients with abnormal SPEP results, only 9 had diagnoses unrelated to PCD. Using the FLC assay in conjunction with retrospective reviews of medical records, we obtained an 86% detection rate of PCD. This detection rate increased to 100% when both SPEP and FLC results were considered. In conclusion, this study documents an important role for serum FLC assays in diagnosing and monitoring PCD in a VA population. Our results support previously established serum FLC reference ranges that were obtained in younger, male and female populations. Using the serum FLC results in conjunction with SPEP results improves the sensitivity and specificity for managing VA patients whose clinical presentation indicates the need to evaluate PCD.     

Biphenotypic plasma cell myeloma: two cases of plasma cell neoplasm with a coexpression of kappa and lambda light chains

Plasma cell neoplasm (PCM) is a medullary and extra medullary proliferation of clonal plasma cells that occurs due to accidental translocation of proto-oncogenes into immunoglobulin (Ig) gene loci. While the majority of plasma cell neoplasms are monoclonal, up to 2% of the PCMs [1] considered being biclonal based on electrophoretic analysis, characterized by secretion of paraprotein with two distinct heavy chains or light chains are possible and present unique diagnostic challenges. Methods: Traditionally protein electrophoresis has been used to diagnose, characterize, and monitor progression of plasma cell neoplasm. To characterize neoplastic plasma cells, in our institution, other ancillary studies, including in situ hybridization, flow cytometric analyses of plasma cell surface markers and cytoplasmic immunoglobulins with DNA ploidy, are also utilized routinely. Results: We present two cases of plasma cell myeloma in which the neoplastic plasma cells shows production of cytoplasmic kappa and lambda light chain, with secretion of free lambda light chain only. Co-expression of kappa and lambda light chain by the same neoplastic plasma cells is a rare but reported phenomenon. Conclusions: Our study indicates that serum electrophoresis alone could mischaracterize biphenotypic myeloma as monotypic plasma cell myelomas in the absence of additional testing methods.     

Light chain types of IgD in human bone marrow and serum.

One of the unexplained features of human IgD is its preferential expression with either kappa or lambda light chains in different situations. While the membrane IgD on B lymphocytes shows a predominance of the kappa type, about 90% of all known IgD myeloma proteins and 87% of normal IgD producing plasma cells in spleens of healthy individuals were shown to belong to the lambda type. Very little is known of the kappa/lambda light chain distribution of normal polyclonal IgD in the serum and in the bone marrow plasma cells. In this study, the kappa/lambda representation of IgD in bone marrow plasma cells and in the serum of 25 adult persons (two healthy and 23 suffering from various nonmalignant diseases) was investigated. The kappa/lambda ratio of IgD+ bone marrow plasma cells showed a large variation among the individuals of this group, in 84% of the cases being below 1.0. While about 1/3 of the investigated subjects had 80% or more of IgD of the lambda type (kappa/lambda ratio below 0.2), most showed a kappa/lambda ratio of IgD higher than that, with four persons exhibiting a clear cut predominance of IgD of the kappa type. A positive correlation (Spearman's correlation co-efficient, P = 0.005) between the percentages of IgD+ plasma cells and their kappa/lambda ratio was found. Semiquantitative evaluation of the kappa/lambda composition within the serum IgD by immunoselection was in agreement with the kappa/lambda ratio of IgD+ plasma cells in all individual cases.     

Quantitation of immunoglobulin isotypes in chronic lymphocytic leukaemic cells compared with normal adult and neonatal lymphocytes

Radioimmunoassays were used to measure the total cellular content of mu, gamma, alpha, delta, kappa and lambda immunoglobulin chains in peripheral blood lymphocytes from normal adults, neonates and 11 patients with chronic lymphocytic leukaemia (CLL). Normal adult lymphocytes contained all classes of immunoglobulin, but predominantly IgG, associated with both types of light chain (kappa:lambda ratio 2:1). In contrast, mu was the major heavy chain in cells from 10 of the CLL patients, and the small amount of IgG found in CLL cells was not produced by the leukaemic clone. Approximately equimolar amounts of one type of light chain were also present, indicating monoclonality. The class distribution of the immunoglobulin in the neonatal cells was intermediate between that of CLL and normal adult cells. CLL B cells had substantially less surface IgM than normal but more cytoplasmic IgM. These data demonstrate the immaturity of neonatal B cells and suggest that CLL cells are also immature--at a stage not normally found in the adult circulation.     

Biclonal light chain gammopathy in multiple myeloma--a case report]

A 74-year-old woman was admitted to our hospital in March 1998 for low-back pain. In 1990, she had a chemotherapy for diffuse mixed cell lymphoma. Biochemical and serologic assays revealed a total protein level of 9.7 g/dl and an IgG level of 4,530 mg/dl. Immunoelectrophoresis showed monoclonal IgG protein associated with two monoclonal kappa and lambda light chain components. Bone marrow examination showed proliferation of myeloma cells comprising up to 25% of all nucleated cells. Myeloma cells were immunohistochemically positive for IgG and kappa and lambda light chains. IgG contained equal amounts of IgG 1 and IgG 2 subtypes and the complementarity determining region 3 (CDR 3) of myeloma cells showed oligoclonality by polymerase chain reaction, suggesting the myeloma cells may have two components. The patient received melphalan and prednisone in combination, resulting in only a minor response. She eventually developed angioimmunoblastic T-cell lymphoma. Biclonal gammopathy associated with malignant lymphoma is rare in case of multiple myeloma and may provide some insight into the pathogenesis of plasma cell tumors.     

T helper cell recognition of idiotopes on lambda 2 light chains of M315 and T952: evidence for dependence on somatic mutations in the third hypervariable region

Previous work has indicated that BALB/c T helper cells (Th) recognize an idiotope expressed on a 88-114/117 fragment of V lambda 2 of BALB/c myeloma protein 315. In the present study the antigenic structure of this idiotope was further analyzed. Conventional carrier-specific Th elicited by immunization of BALB/c mice with free lambda 2(315) did not cross-react with the free lambda 2 chain of the BALB/c myeloma protein T952 which differs from lambda 2(315) in five amino acid positions (38, 94, 95, 96, 99). Similarly, Th primed with free lambda 2T952 did not respond to a boost with free lambda 2(315). Thus, BALB/c lambda 2(315)-specific Th recognize an idiotope that depends on some or all of the residues at positions 94, 95, 96 and 99. Furthermore, free lambda 2T952 contains an idiotope immunogenic to Th that depends on some or all of residues 38, 94, 95, 96 and 99. Th recognition of the free lambda 2T952 idiotope was quenched upon H + L chain assembly because Th elicited by free lambda 2T952 did not respond to a boost with the complete T952 myeloma protein. In contrast to the lack of Th cell cross-reactivity, some of the antisera from BALB/c mice immunized with free lambda 2T952 cross-reacted with free lambda 2(315), free lambda lJ558 and free lambda 3CBPC49 but not with free kappa W3129 or polyclonal L chains. The H chain of T952 (alpha, kappa 2) myeloma protein was abnormally short (Mr = 48 000) and T952 existed as a halfmere probably due to this H chain deletion. Furthermore, H and L chains were disulfide bonded to each other.     

Lack of isotype exclusion and expression of aberrant lambda light chain on secreted MOPC-315 myeloma proteins

The presence of aberrant lambda 1 light (L) chain fragment (lambda 1 F) on the secreted myeloma protein of MOPC-315 has been demonstrated by serological and immunochemical methods. We developed a highly sensitive radioimmunoassay that utilizes exquisitely specific xenogeneic anti-lambda 1 antibodies to detect the minute amounts of lambda 1 F on lambda 2-bearing MOPC-315 myeloma proteins. In addition, structural evidence that lambda 1 F is present on MOPC-315 myeloma protein was demonstrated by subjecting 125I-labeled MOPC-315 myeloma protein to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions followed by autoradiography. The relative amounts of lambda 1 F and lambda 2-chain on MOPC-315 myeloma were measured by two independent methods. The molar ratio of lambda 1 F to lambda 2 was calculated to be 1:68 by radioimmunoassay and 1:80 by analytical SDS-PAGE. This represents the first demonstration that an aberrant L-chain fragment combines with a heavy chain and is secreted in association with antigen-binding myeloma proteins. The implications of these results on L-chain isotype exclusion are discussed.     

Characterization of IgD

Human IgD present in the serum of normal individuals or of patients with Hodgkin's disease (having high IgD concentrations) was characterized and compared with five IgD myeloma proteins. IgD was isolated using a highly specific anti-delta insoluble immunoabsorbent from which the bound material was eluted with sodium dodecyl sulphate (SDS) or urea. The latter reagent could be removed by extensive dialysis, thus making possible the renaturation of the eluted molecules. The purity of the IgD thus isolated was confirmed by antigenic analysis. Both kappa and lambda light chain determinants were present on serum IgD, although lambda light chain was predominant with a ratio over the kappa chain of 2:1. SDS-polyacrylamide slab gel electrophoresis analysis revealed two different molecular forms of serum IgD, one (IgD) migrating identically to monoclonal IgD, the other (IgD2) having a faster mobility. The difference between the two molecules was entirely, due to the different sizes of their constituent delta chains. Peptide mapping of the two chains (delta1 and delta2 respectively) and of the delta chain of an IgD myeloma protein was carried out using 125I-labelled material. The three molecules displayed a high degree of homology, the delta2 chain differing by the presence of three characteristic extra peptides. The significance of these extra peptides is discussed in the light of the peptide mapping technique employed.     

Immunoquantitation of free light chain immunoglobulins: applications in multiple myeloma.

A single radial immunodiffusion (RID) assay for the free lambda (lambda) and kappa (kappa) light chain (LC) immunoglobulins was developed for study of clinical samples of serum, urine, and bone marrow of patients with multiple myeloma. Using highly specific rabbit anti-LC sera, we were able to quantitate: (a) free serum LC after fractionating the serum sample using an Amicon ultrafiltration chamber equipped with an XM100A diaflow membrane and an 125I-LC standard for calculating filtration efficiencies, (b) directly, Bence Jones (BJ) proteins in the urine, and (c) the in vitro LC synthesis by myeloma plasma cells obtained from bone marrow aspirates. The median values of free LC levels in sera (n = 12), urines (n = 25), and marrow culture synthetic rates (n = 17) were 116.2 mg/dl, 0.775 g/day and 15.3 pg/plasma cell/day, respectively. These data were useful in initial evaluation of patients and serial follow-up studies. The assays have also been of use in our research on the determination of total body tumor mass in patients with BJ multiple myeloma.     

Relationship between monoclonal gammopathy and cardiac amyloid type

BackgroundProper 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.MethodsRetrospective analysis of two tertiary care populations (n=143, 2001–2010), of cardiac biopsy-proven amyloidosis, was performed.ResultsAmyloid 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%).ConclusionsATTR 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.SummaryThis 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.     

Serum Immunoglobulin Free Light Chains in Severe Forms of Atopic Dermatitis

An increase in immunoglobulin free light chains (FLC) was recently described in several pathological conditions, including asthma. FLC pathology is classically associated with monoclonal gammopathies. Its association with allergic disorders is surprising and unexplained. We therefore tested a cohort of children with severe atopic dermatitis (SCORAD 50–80) to determine the serum levels of free kappa and lambda chains, and correlated the results with clinical status and relevant laboratory markers. Seventy‐three patients with severe forms of AD, all children from 3 months to 3 years of age and ninety healthy age‐matched controls were included in the study. Light chains in sera were tested using the Freelite assay (Binding Site, Birmingham, UK). There were highly significant differences in both kappa (mean: 7.05 and 3.22 mg/l) and lambda (mean: 10.99 and 9.8 mg/l) serum levels between patients and controls, respectively (P < 0.0001). The kappa/lambda ratio in patients with allergy (mean: 0.64) was significantly higher than in controls (0.33) (P < 0.0001). We further observed significantly increased levels of FLC and their ratio in the group of patients with severe forms of AD in comparison to the group of patients with a resting stage of the disease or healthy controls (P < 0.05 and P < 0.0001, respectively). On the other hand, we could not confirm any association of FLC levels with age or total IgE levels. In conclusion, an increase in FLC reflects disease activity in children with severe atopic dermatitis. FLC might thus represent an additional diagnostic marker independent of total IgE levels.