The importance of serum immunoglobulin free light chain assay in AL amyloidosis
Authors:
T. Pika 1; P. Lochman 2; J. Minařík 1; J. Bačovský 1; V. Ščudla 1
Authors‘ workplace:
III. interní klinika – nefrologická, revmatologická, endokrinologická, LF UP a FN Olomouc
1; Oddělení klinické biochemie, FN Olomouc
2
Published in:
Transfuze Hematol. dnes,19, 2013, No. 3, p. 134-138.
Category:
Comprehensive Reports, Original Papers, Case Reports
Overview
Introduction.
Systemic AL amyloidosis is a rare illness in the group of monoclonal gammopathies. The disease is based on extracellular deposition of insoluble fibrils formed by complete monoclonal light immunoglobulin chains or their fragments, produced by clonal plasmocytes. Identification of the plasmocyte clone, or of its protein product – the monoclonal immunoglobulin (MIg) – represents a key aspect of diagnostics and monitoring of AL amyloidosis patients. Serum immunoglobulin free light chain (FLC) assay, routinely performed in the recent years, significantly widened the options for MIg analysis in monoclonal gammopathies. The subject of this report is practical experience with serum immunoglobulin free light chains assay in AL amyloidosis patients.
Patients and Methods.
The patient set comprised 19 patients with biopsy-verified systemic AL amyloidosis. Age median was 62 years of age (48–92 years of age), male to female ratio was 16 : 3, representation of secretion kappa : lambda was 3 : 16. Free light chains serum levels were determined by the FreeLiteTM system. Normal range of serum levels was 3.3–19.4 mg/l for light chain kappa (κ), and 5.7–26.3 mg/l for light chain lambda (λ). Mutual ratio of light chains kappa/lambda (the κ/λ index) was determined by a calculation with normal range 0.26–1.65, in case of renal insufficiency 0.37–3.1.
Results.
MIg serum levels were determined in 12 out of 18 (68%) patients, where the median level was 1.69 g/l (0–9.8 g/l). As for isotypes, there were 4 cases of complete isotype IgG (2x IgG-κ, 2x IgG-λ), 3 cases of IgA-λ, and one patient presented the isotype IgD-λ. Light chains λ only were found in the serum of 4 patients. Protein analysis of urine found excretion of Bence-Jones protein in 11 patients, in all cases in quantity over 200 mg/24 hours, while the presence of complete MIg molecules in the urine (1x IgA-λ, 1x IgG-λ) was additionally determined in 2 patients. Serum immunoglobulin free light chain assay determined abnormal levels in all patients with median value 399 mg/l (54.4–2 385 mg/l), while κ/λ index pathology was determined in 17 (90%) patients. Out of the 17 patients with abnormal FLC levels and concomitant κ/λ index pathology, 16 patients had dFLC levels > 50 mg/l (dFLC = difference between dominant and alternative FLC levels). Therefore, FLC assay enables regular monitoring of the disease in 16 out of 19 (84%) patients.
Conclusion.
Serum immunoglobulin free light chain assay currently represents a key laboratory parameter not only for dia-gnostics and monitoring of the course of the disease, but namely for treatment efficacy evaluation. A combination of standard MIg detection techniques with FLC level assay enables monitoring of a vast majority of AL amyloidosis patients.
Key words:
AL amyloidosis, free light immunoglobulin chains, disease monitoring
Sources
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Haematology Internal medicine Clinical oncologyArticle was published in
Transfusion and Haematology Today
2013 Issue 3
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