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Biological variation of free light chains in serum
Clinica Chimica Acta 427 (2014) 27–28
Contents lists available at ScienceDirect
Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim
Letter to the Editor Biological variation of free light chains in serum
We read with interest the paper by Braga et al. published earlier in this journal [1], regarding the biological variation of the free light chains in serum, as well as the comment made by Zaninotto et al. [2]. The serum free light chain (sFLC) analysis is a well established method for diagnostic use in the hematological field, particularly in the monitoring of monoclonal plasma cell dyscrasias (PCD), though there are some well known technical limitations of the assay, which potentially affect the use in serial measurements. We agree on the importance of establishing data on the biological variation of the sFLC, thereby being able to assess the size of the reference change value (RCV). Our study group has published data on biological variation in ostensible healthy individuals, as well as in patients with PCD [3], 6 were diagnosed with multiple myeloma (MM) and 5 with monoclonal gammopathy of unknown significance (MGUS). The studied patients all had either κ or λ FLC above the upper reference interval, and an abnormal κ/λ-ratio. The patients received no anti-myeloma treatment in the study period. The means and absolute ranges of each studied individual are shown in Fig. 1. As illustrated by the error bars the intra-individual biological variation (CVw) is similar between the three groups studied (healthy, persons with MGUS and patients with MM) (κ, P = 0.335; λ, P = 0.152). All participants were studied with 8 blood samples over a study period of 5 days. Our calculated intraindividual biological variation of 4.3% and 7.0% for κ and λ, respectively, are much smaller than the 54.5% Katzmann et al. found when determining a long-term biological variation of sFLC in patients with PCD [4]. A calculated biological variation based on specimens taken at intervals of less than one week might show smaller variation and might lead to an underestimation of CVw [5]. The data, however, are consistent with the results obtained by Braga et al. [1]. Determining biological variation in patients with PCD over a time period of as long as five years seems problematic, both due to the normal evolution of the monoclonal plasma cell diseases and the analytical aspects of the currently used assay from FreeLite™ (the Binding Site Ltd., Birmingham, UK). As described by Tate et al. [6] the analytical variation is highly dependent on numbers of different lots of reagents used in the assessment of the analytical variation. They found a median between-reagent lot variation for FLC measurement
0009-8981/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cca.2013.09.020
that was 19–20% CV [6]. Therefore it is possible, that the high biological variation in part can be explained by an inherent analytical component. In our study we found an analytical variation measured over 4 different lots of reagents to be 7.3% and 4.5% for κ and λ, respectively. Braga et al. [1] measured only the intra-assay variation, which explains the very small analytical variation used in their calculations of the RCV. Our calculated RCV is 24% and 23% for κ and λ, respectively. For clinicians dealing with the treatment and monitoring of patients with monoclonal PCD, awareness of the RCV is an important tool, since it will have an impact in decision-making with respect to when a change in sFLC levels can be taken as evidence of progression of the disease or response to treatment. References [1] Braga F, Infusino I, Dolci A, Panteghini M. Biological variation of free light chains in serum. Clin Chim Acta 2013;415:10–1. [2] Zaninotto M, Altinier S, Varagnolo M, Plebani M. Biological variation of free light chains in serum. Clin Chim Acta 2013;418:72. [3] Hansen CT, Münster AM, Nielsen L, Pedersen P, Abildgaard N. Clinical and preclinical validation of the serum free light chain assay: identification of the critical difference for optimized clinical use. Eur J Haematol 2012;89:458–68. [4] Katzmann JA, Snyder MR, Rajkumar SV, Kyle RA, Therneau TM, Benson JT, et al. LongTerm Biological Variation of Serum Protein Electrophoresis M-Spike, Urine M-Spike, and Monoclonal Serum Free Light Chain Quantification: Implications for Monitoring Monoclonal Gammopathies. Clin Chem 2011;57:1687–92. [5] Fraser CG, Harris EK. Generation and Application of Cata on Biological Variation in Clinical Chemistry. Crit Rev Clin Lab Sci 1989;27:409–37. [6] Tate JR, Mollee P, Dimeski G, Carter AC, Gill D. Analytical performance of serum free light-chain assay during monitoring of patients with monoclonal light-chain diseases. Clin Chim Acta 2007;376:30–6.
Charlotte Toftmann Hansen Department of Hematology, Odense University Hospital, Klovervaenget 10, 12th floor, 5000 Odense C, Denmark Corresponding author. Tel.: +45 24428085; fax: +45 66138759. E-mail address: [email protected]. Niels Abildgaard Department of Hematology, Odense University Hospital, Denmark 29 August 2013
28
Letter to the Editor
A
C
Kappa
Lambda
Diurnal variation
Diurnal variation λ reference interval
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Individuals
Individuals
κ reference interval
Multiple myeloma MGUS Healthy 1
10
100
1000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
*
1
10
Kappa, mg/L
B
D
Kappa
10
100
Kappa, mg/L
1000
Day-to-day variation
λ reference interval
Individuals
Individuals
*
1
1000
Lambda
Day-to-day variation
κ reference interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
100
Lambda, mg/L
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1
10
100
1000
Lambda, mg/L
Fig. 1. Study of biological variation. The diurnal and day-to-day biological variation for kappa and lambda free light chains in serum. The means and absolute ranges (error bars) on a logarithmic scale for six patients with multiple myeloma, five persons with MGUS and seven healthy individuals evaluated for diurnal (A) and day-to-day (B) variation of κ FLC and diurnal (C) and day-to-day (D) variation of λ FLC. The upper and lower reference intervals for κ and λ FLC are illustrated with hatched lines. Asterisks indicate outliers according to Reeds criteria. The within-person variation is small compared to the reference interval and similar in the three groups (multiple myeloma, MGUS and healthy individuals) (3). FLC: free light chains; MGUS: monoclonal gammopathy of unknown significance.
Contents lists available at ScienceDirect
Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim
Letter to the Editor Biological variation of free light chains in serum
We read with interest the paper by Braga et al. published earlier in this journal [1], regarding the biological variation of the free light chains in serum, as well as the comment made by Zaninotto et al. [2]. The serum free light chain (sFLC) analysis is a well established method for diagnostic use in the hematological field, particularly in the monitoring of monoclonal plasma cell dyscrasias (PCD), though there are some well known technical limitations of the assay, which potentially affect the use in serial measurements. We agree on the importance of establishing data on the biological variation of the sFLC, thereby being able to assess the size of the reference change value (RCV). Our study group has published data on biological variation in ostensible healthy individuals, as well as in patients with PCD [3], 6 were diagnosed with multiple myeloma (MM) and 5 with monoclonal gammopathy of unknown significance (MGUS). The studied patients all had either κ or λ FLC above the upper reference interval, and an abnormal κ/λ-ratio. The patients received no anti-myeloma treatment in the study period. The means and absolute ranges of each studied individual are shown in Fig. 1. As illustrated by the error bars the intra-individual biological variation (CVw) is similar between the three groups studied (healthy, persons with MGUS and patients with MM) (κ, P = 0.335; λ, P = 0.152). All participants were studied with 8 blood samples over a study period of 5 days. Our calculated intraindividual biological variation of 4.3% and 7.0% for κ and λ, respectively, are much smaller than the 54.5% Katzmann et al. found when determining a long-term biological variation of sFLC in patients with PCD [4]. A calculated biological variation based on specimens taken at intervals of less than one week might show smaller variation and might lead to an underestimation of CVw [5]. The data, however, are consistent with the results obtained by Braga et al. [1]. Determining biological variation in patients with PCD over a time period of as long as five years seems problematic, both due to the normal evolution of the monoclonal plasma cell diseases and the analytical aspects of the currently used assay from FreeLite™ (the Binding Site Ltd., Birmingham, UK). As described by Tate et al. [6] the analytical variation is highly dependent on numbers of different lots of reagents used in the assessment of the analytical variation. They found a median between-reagent lot variation for FLC measurement
0009-8981/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cca.2013.09.020
that was 19–20% CV [6]. Therefore it is possible, that the high biological variation in part can be explained by an inherent analytical component. In our study we found an analytical variation measured over 4 different lots of reagents to be 7.3% and 4.5% for κ and λ, respectively. Braga et al. [1] measured only the intra-assay variation, which explains the very small analytical variation used in their calculations of the RCV. Our calculated RCV is 24% and 23% for κ and λ, respectively. For clinicians dealing with the treatment and monitoring of patients with monoclonal PCD, awareness of the RCV is an important tool, since it will have an impact in decision-making with respect to when a change in sFLC levels can be taken as evidence of progression of the disease or response to treatment. References [1] Braga F, Infusino I, Dolci A, Panteghini M. Biological variation of free light chains in serum. Clin Chim Acta 2013;415:10–1. [2] Zaninotto M, Altinier S, Varagnolo M, Plebani M. Biological variation of free light chains in serum. Clin Chim Acta 2013;418:72. [3] Hansen CT, Münster AM, Nielsen L, Pedersen P, Abildgaard N. Clinical and preclinical validation of the serum free light chain assay: identification of the critical difference for optimized clinical use. Eur J Haematol 2012;89:458–68. [4] Katzmann JA, Snyder MR, Rajkumar SV, Kyle RA, Therneau TM, Benson JT, et al. LongTerm Biological Variation of Serum Protein Electrophoresis M-Spike, Urine M-Spike, and Monoclonal Serum Free Light Chain Quantification: Implications for Monitoring Monoclonal Gammopathies. Clin Chem 2011;57:1687–92. [5] Fraser CG, Harris EK. Generation and Application of Cata on Biological Variation in Clinical Chemistry. Crit Rev Clin Lab Sci 1989;27:409–37. [6] Tate JR, Mollee P, Dimeski G, Carter AC, Gill D. Analytical performance of serum free light-chain assay during monitoring of patients with monoclonal light-chain diseases. Clin Chim Acta 2007;376:30–6.
Charlotte Toftmann Hansen Department of Hematology, Odense University Hospital, Klovervaenget 10, 12th floor, 5000 Odense C, Denmark Corresponding author. Tel.: +45 24428085; fax: +45 66138759. E-mail address: [email protected]. Niels Abildgaard Department of Hematology, Odense University Hospital, Denmark 29 August 2013
28
Letter to the Editor
A
C
Kappa
Lambda
Diurnal variation
Diurnal variation λ reference interval
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Individuals
Individuals
κ reference interval
Multiple myeloma MGUS Healthy 1
10
100
1000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
*
1
10
Kappa, mg/L
B
D
Kappa
10
100
Kappa, mg/L
1000
Day-to-day variation
λ reference interval
Individuals
Individuals
*
1
1000
Lambda
Day-to-day variation
κ reference interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
100
Lambda, mg/L
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1
10
100
1000
Lambda, mg/L
Fig. 1. Study of biological variation. The diurnal and day-to-day biological variation for kappa and lambda free light chains in serum. The means and absolute ranges (error bars) on a logarithmic scale for six patients with multiple myeloma, five persons with MGUS and seven healthy individuals evaluated for diurnal (A) and day-to-day (B) variation of κ FLC and diurnal (C) and day-to-day (D) variation of λ FLC. The upper and lower reference intervals for κ and λ FLC are illustrated with hatched lines. Asterisks indicate outliers according to Reeds criteria. The within-person variation is small compared to the reference interval and similar in the three groups (multiple myeloma, MGUS and healthy individuals) (3). FLC: free light chains; MGUS: monoclonal gammopathy of unknown significance.