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

Taegeun Lee; Chan-Jeoung Park; Miyoung Kim; Young-Uk Cho; Seongsoo Jang; Sang-Hyun Hwang; Jung-Hee Lee; Dok Hyun Yoon

doi:10.5045/br.2023.2022232

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Original Article

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Blood Res 2023; 58(1):

Published online March 31, 2023

https://doi.org/10.5045/br.2023.2022232

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

Taegeun Lee¹, Chan-Jeoung Park¹, Miyoung Kim¹, Young-Uk Cho¹, Seongsoo Jang¹, Sang-Hyun Hwang¹, Jung-Hee Lee², Dok Hyun Yoon³

Author Info. +

Departments of 1Laboratory Medicine, 2Hematology, and 3Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

Correspondence to : Chan-Jeoung Park, M.D., Ph.D.
Department of Laboratory Medicine, Asan Medical Center and University of Ulsan College of Medicine, 88 Olympic-ro 43 gil, Songpa-gu, Seoul 05505, Korea
E-mail: cjpark@amc.seoul.kr

Received: December 1, 2022; Revised: February 25, 2023; Accepted: March 20, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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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.

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Keywords: Light-chain (AL) amyloidosis, Monoclonality, Bone marrow findings, Serum free light chain ratio, Immunohistochemistry, Flow cytometry

Article

Original Article

Blood Res 2023; 58(1): 71-76

Published online March 31, 2023 https://doi.org/10.5045/br.2023.2022232

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

Taegeun Lee¹, Chan-Jeoung Park¹, Miyoung Kim¹, Young-Uk Cho¹, Seongsoo Jang¹, Sang-Hyun Hwang¹, Jung-Hee Lee², Dok Hyun Yoon³

Departments of 1Laboratory Medicine, 2Hematology, and 3Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

Correspondence to:Chan-Jeoung Park, M.D., Ph.D.
Department of Laboratory Medicine, Asan Medical Center and University of Ulsan College of Medicine, 88 Olympic-ro 43 gil, Songpa-gu, Seoul 05505, Korea
E-mail: cjpark@amc.seoul.kr

Received: December 1, 2022; Revised: February 25, 2023; Accepted: March 20, 2023

Abstract

Keywords: Light-chain (AL) amyloidosis, Monoclonality, Bone marrow findings, Serum free light chain ratio, Immunohistochemistry, Flow cytometry

Abstract

Table 1 . Bone marrow and related laboratory findings according to bone marrow involvement in 98 cases of AL amyloidosis..

Parameters	Bone marrow involved patients (N=35)	Bone marrow non-involved patients (N=63)	P
κ/λ clonality^a)	8/27	26/37	0.067
% plasma cells in bone marrow, mean (range)	8.4 (1.2–49.2)	11.0 (0.0–92.4)	0.360^b)
M-component detection by serum and urine protein electrophoresis	57.1% (20/35)	60.3% (38/63)	0.759
Monoclonality detection by serum and urine immunofixation electrophoresis	80.0% (28/35)	79.4% (50/63)	0.940
Abnormal serum free light chain ratio	91.2% (31/34)	72.2% (39/54)	0.032
Monoclonality detected by immunohistochemistry	82.9% (29/35)	87.3% (55/63)	0.547
Aberrant plasma cells by flow cytometric assay	93.3% (14/15)	92.6% (25/27)	1.000^c)

^a)The number of cases which showed κ or λ clonality. ^b)The Mann-Whitney U test was used for this comparison. ^c)Fisher’s exact test was used for this comparison, and the Chi-squared test was used for other comparisons of categorical data..

Table 2 . The discrepancies between laboratory tests detecting light-chain clonality and aberrant plasma cells by flow cytometric assay..

Cases	N	Plasma cell %	κ/λ clonality	IFE (+)	SFLC ratio (Abn)	IHC (+)	FCM assay (+)
IFE (-)	20	2.5 (0.8–52.0)	15/5	NA	10/16	17/20	3/3
SFLC ratio (N)	18	5.1 (1.2–26.8)	5/13	12/18	NA	15/18	7/7
IHC (-)	14	4.0 (0–18.8)	1/13	11/14	13/13	NA	1/3
FCM assay (-)	3	6.8 (3.2–9.6)	0/3	3/3	3/3	1/3	NA

Abbreviations: Abn, abnormal; FCM, flow cytometric; IFE, immunofixation electrophoresis; IHC, immunohistochemistry; N, normal; NA, not applicable; SFLC, serum free light chain..

Table 3 . Amyloid deposition in bone marrow biopsies or clot sections in 98 cases of AL amyloidosis..

Amyloid deposit grade^a)	Cases (N=98)	% plasma cells, median (range)	λ (N=64)	κ (N=34)	P
Bone marrow					0.887^b)
0	63 (64.3%)	11.0 (0.0–92.4)	37	26
1+	11 (11.2%)	5.6 (1.2–27.2)	8	3
2+	12 (12.2%)	8.2 (3.6–49.2)	9	3
3+	12 (12.2%)	14.3 (2.4–35.0)	10	2

^a)Amyloid deposit grade: 1+, blood vessels only; 2+, interstitial deposition of ≤2 high-power fields; 3+, interstitial deposition of >2 high-power fields. ^b)Fisher’s exact test was used for this comparison..

Table 4 . Amyloidosis detection methods and bone marrow findings in 35 cases of AL amyloidosis with bone marrow involvement..

N	22	3	10
Detection method
Congo red stain by polarizing microscopy	Positive	Negative	Negative
Congo red stain by light microscopy	Positive	Positive	Negative
PAS stain	Positive	Positive	Positive
Amyloid deposit grade score^a)
Median (range)	2+ (1+–3+)	2+ (1+–3+)	2+ (1+–3+)
% plasma cells in bone marrow
Median (range)	7.6 (1.2–49.2)	18.0 (2.8–23.4)	8.2 (1.6–35.0)

^a)Amyloid deposit grade: 1+, blood vessels only; 2+, interstitial deposition of ≤2 high-power fields; 3+, interstitial deposition of >2 high-power fields..