Zhenduanxue lilun yu shijian (Apr 2023)
A comparative study on the value of urine free light chain and urine total light chain assays in quantitative monitoring of urine light chain
Abstract
Objective: To explore whether the novel urine free light chain (uFLC) assay is superior to the traditional urine total light chain (uTLC) assay in quantitative monitoring of urine light chain. Methods: A total of 458 paired samples of blood and were collected from 280 patients (including 153 patients with plasma cell diseases and 137 patients with non-plasma cell diseases) from January 2022 to March 2023 at Ruijin Hospital， Shanghai Jiao Tong University School of Medicine. The positive concordance rates and correlations between the κ value, λ value and κ/λ ratio of uFLC and uTLC assays with the results of urinary immunofixation electrophoresis (uIFE) and serum free light chain (sFLC) were analyzed by Chi-squared test, MeNemar’s test and Spearman correlation coefficient calculation. Result: Among the 102 uIFE positive samples, 88.2% (90/102) of the samples had abnormal uFLC κ/λ ratio, and 87.3% (89/102) had abnormal uTLC κ/λ ratio (P<0.001). Among the 183 samples with abnormal sFLC κ/λ ratio, 65.6% (120/183) of the samples had abnormal uFLC κ/λ ratio, and 51.4% (94/183) had abnormal uTLC κ/λ ratio (P<0.001). Among the 457 samples with both uFLC and uTLC results, 164 samples (35.9%) had abnormal uFLC κ/λ ratio, and 123 samples (26.9%) had abnormal uTLC κ/λ ratio (P<0.001). There was a strong correlation between the levels of κ light chain, λ light chain, and κ/λ ratio of uFLC and uTLC (r values were 0.849, 0.697 and 0.648, respectively, P<0.001). The r values between the levels of corresponding κ light chain, λ light chain, and κ/λ ratio of uFLC and sFLC were 0.628, 0.552, and 0.640 (P<0.001), while the r values between the levels of κ light chain, λ light chain, and κ/λ ratio of uTLC assay and sFLC assay were 0.520, 0.533, and 0.551, respectively (P<0.001). Moderate correlations were indicated and the correlation between uFLC and sFLC was stronger than that between uTLC and sFLC. Conclusions: Compared with the uTLC assay, the uFLC assay is more sensitive in the quantitative monitoring of urine light chain and has higher positive concordance rates and stronger correlations with uIFE and sFLC results, indicating an objective quantitative determination of urine light chain. It is recommended to prioritize the use of uFLC assay in clinical quantitative monitoring of urinary light chain.
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